Atmospheric Environment (v.96, #C)

Probabilistic safety analysis for urgent situations following the accidental release of a pollutant in the atmosphere by P. Armand; F. Brocheton; D. Poulet; F. Vendel; V. Dubourg; T. Yalamas (1-10).
This paper is an original contribution to uncertainty quantification in atmospheric transport & dispersion (AT&D) at the local scale (1–10 km). It is proposed to account for the imprecise knowledge of the meteorological and release conditions in the case of an accidental hazardous atmospheric emission. The aim is to produce probabilistic risk maps instead of a deterministic toxic load map in order to help the stakeholders making their decisions. Due to the urge attached to such situations, the proposed methodology is able to produce such maps in a limited amount of time. It resorts to a Lagrangian particle dispersion model (LPDM) using wind fields interpolated from a pre-established database that collects the results from a computational fluid dynamics (CFD) model. This enables a decoupling of the CFD simulations from the dispersion analysis, thus a considerable saving of computational time. In order to make the Monte-Carlo-sampling-based estimation of the probability field even faster, it is also proposed to recourse to the use of a vector Gaussian process surrogate model together with high performance computing (HPC) resources. The Gaussian process (GP) surrogate modelling technique is coupled with a probabilistic principal component analysis (PCA) for reducing the number of GP predictors to fit, store and predict. The design of experiments (DOE) from which the surrogate model is built, is run over a cluster of PCs for making the total production time as short as possible. The use of GP predictors is validated by comparing the results produced by this technique with those obtained by crude Monte Carlo sampling.Accidental toxic release in a built environment – risk map (at 1.5 m above the ground level) emphasizing the safe (risk is less than 2.5%), dangerous (risk is greater than 97.5%) and uncertain zones (risk is comprised between 2.5% and 97.5%), estimated using Monte Carlo sampling with 10,000 runs of the vector GP surrogate model. The orange line corresponds to the median critical toxic load contour level while the black line corresponds to that obtained from the deterministic risk assessment study.Display Omitted
Keywords: Atmospheric transport and dispersion; Uncertainty quantification; Surrogate modelling; Gaussian process predictor; Principal component analysis;

Aerosol chemical and physical properties were measured in 2010 at Neumayer research station, Antarctica. Samples for chemical analysis (ion chromatography) were collected using a Teflon/Nylon filter combination (TNy) sampler, and with a multi stage low pressure impactor (SDI). Particle number concentration was measured continuously with a Grimm OPC optical particle counter. Total particle number concentration varied largely throughout the year, and the highest number concentrations for particles larger than 0.3 μm were observed simultaneously with the highest sea salt concentrations. About 50% of the sea salt aerosol mass was found in the submicron size range. Below 0.2 μm of particle aerodynamic diameter the contribution of sea salt aerosols was negligible. Further analysis showed that sea salt aerosols had undergone physico-chemical processes, either during the transportation, or during their formation. High degree of chloride depletion was observed during austral summer, when the presence of acidic gases exhibit their characteristic seasonal maximum. Apart from chloride depletion, excess chloride relating to sodium was also detected in one SDI sample, indicating actually a sodium depletion by mirabilite formation on freshly formed sea ice areas. Analysis of selected episodes showed that the concentration of sea salt particles, their modal structure, and their chemical composition is connected with their source areas, their formation mechanisms, and local transport history.
Keywords: Antarctica; Sea salt modification; Mass size distribution; Particle number concentration;

Time evolution of atmospheric particle number concentration during high-intensity pyrotechnic events by Javier Crespo; Eduardo Yubero; Jose F. Nicolás; Sandra Caballero; Nuria Galindo (20-26).
The Mascletàs are high-intensity pyrotechnic events, typical of eastern Spanish festivals, in which thousands of firecrackers are burnt at ground level in an intense, short-time (<8 min) deafening spectacle that generates short-lived, thick aerosol clouds. In this study, the impact of such events on air quality has been evaluated by means of particle number concentration measurements performed close to the venue during the June festival in Alicante (southeastern Spain). Peak concentrations and dilution times observed throughout the Mascletàs have been compared to those measured when conventional aerial fireworks were launched 2 km away from the monitoring site. The impact of the Mascletàs on the total number concentration of particles larger than 0.3 μm was higher (maximum ∼2·104 cm-3) than that of fireworks (maximum ∼2·103 cm-3). The effect of fireworks depended on whether the dominant meteorological conditions favoured the transport of the plume to the measurement location. However, the time required for particle concentrations to return to background levels is longer and more variable for firework displays (minutes to hours) than for the Mascletàs (<25 min).
Keywords: Fireworks; Aerosol size-distribution; Optical particle counter; Mascletàs;

Mercury distribution and variation on a high-elevation mountain glacier on the northern boundary of the Tibetan Plateau by Jie Huang; Shichang Kang; Junming Guo; Mika Sillanpää; Qianggong Zhang; Xiang Qin; Wentao Du; Lekhendra Tripathee (27-36).
In July 2013, snow/ice and streamwater samples were retrieved from a high-elevation mountain glacier (Laohugou Glacier No. 12) on the northern boundary of the Tibetan Plateau and were analysed for total Hg (HgT). Concentration levels of HgT in snow samples were higher than those from the central and southern part of the Tibetan Plateau. Most of the Hg in the snow/ice was found to be associated with particulate matter. A small daily variation of HgT in surface snow further suggested that snow Hg on the Tibetan Plateau was less influenced by the effect of post-depositional processes such as photoreduction. The variations in HgT peak concentration on the vertical profiles of the snowpits indicated that settling of particulate matter and percolation of snowmelt had caused an increase in Hg concentrations with increasing depth. No positive relationship was found between HgT and elevation in our study region, indicating that the “altitude effect” on Hg in surface snow may only exist on extremely high-elevation glaciers. Moreover, HgT concentrations in the surface ice were found to be the highest observed in this glacier. With ongoing climate warming, this is of particular concern in western China as the accumulated Hg released by accelerated glacier thinning and retreat may endanger ecosystems and human health in the glacier-fed downstream regions.
Keywords: Mercury; Snow/ice; Distribution; Variation; Laohugou glacier no. 12; Tibetan Plateau;

Mobile measurements were performed to study the spatio-temporal variation of particle number size distributions (NSD) in the range 11 < D p < 365 nm as well as total particle number and black carbon concentrations in Braunschweig, Germany during the winter and summer period 2012/2013. The study area of about 1 km2 consisted of six different outdoor microenvironments (ME) that were classified according to different traffic intensities and dominant land use types along the measurement route.Highest averaged total number concentrations measured at roadside (RO) were 2.5 × 104 pt cm−3 (with a maximum of 7.6 × 104 pt cm−3) during winter and about 1.2 × 104 pt cm−3 on average during the summer campaign. Measurement spots which are more distant to traffic were characterised by lower concentrations of 1.6 × 104 pt cm−3 and 9.0 × 103 pt cm−3 during winter and summer, respectively. Black carbon (BC) concentrations were also clearly related to traffic emissions and resulted in concentrations of 2.8 μg m−3 on average (absolute maximum of 6.2 μg m−3) at RO-sites. The concentrations of particles and BC in the different ME (aggregated from the single measurement spots) documented the concentration of both metrics to be a function of distance of the measurement to fresh traffic emissions.A multiple regression based model was established to identify significant parameters which can be used to model the microscale variation of particle NSD in the outdoor ME. Two models with different numbers of input parameters were calculated. The first contained all measured parameters as input, the second only a reduced number consisting of TNC, BC and wind speed. Both models worked convincingly, even the approach with the limited number of input parameters. The average size integrated (TNC) deviation to observed data in all ME during both seasons was <13%. The best agreement between model and observations is given for the near-traffic ME.
Keywords: Aerosol; Ultrafine particles; Microenvironment; Modelling; Multiple regression; Mobile measurement; Lung deposited surface area;

The amount of Biogenic Volatile Organic Compounds (BVOC) emitted from terrestrial vegetation is of great importance in atmospheric reactivity, particularly for ozone-forming reactions and as condensation nuclei in aerosol formation and growth. This work presents a detailed inventory of isoprenoid emissions from vegetation in Italy using an original approach which combines state of the art models to estimate the species-specific isoprenoid emissions and a Geographic Information System (GIS) where emissions are spatially represented. Isoprenoid species and basal emission factors were obtained by combining results from laboratory experiments with those published in literature. For the first time, our investigation was not only restricted to isoprene and total monoterpenes, but our goal was to provide maps of isoprene and individual monoterpenes at a high-spatial (∼1 km2) and temporal resolution (daily runs, monthly trends in emissions are discussed in the text). Another novelty in our research was the inclusion of the effects of phenology on plant emissions. Our results show that: a) isoprene, a-pinene, sabinene and b-pinene are the most important compounds emitted from vegetation in Italy; b) annual biogenic isoprene and monoterpene fluxes for the year 2006 were ∼31.30 Gg and ∼37.70 Gg, respectively; and c) Quercus pubescens + Quercus petrea + Quercus robur, Quercus ilex, Quercus suber and Fagus sylvatica are the principal isoprenoid emitting species in the country. The high spatial and temporal resolution, combined with the species-specific emission output, makes the model particularly suitable for assessing local budgets, and for modeling photochemical pollution in Italy.
Keywords: Isoprenoids; Monoterpenes; Isoprene; Italian forests; BVOC inventory;

Semi-volatile organic compounds (SVOCs), harmful contaminants to human health, have a strong sorption tendency to the airborne particles, which affects the SVOCs transport process in the air and increases the total SVOC concentration. In this paper, a mathematical model for describing the transport mechanism of SVOCs in the air and interactions with airborne particle was proposed. After validated by Benning et al. (2013)'s experimental results, the numerical results by the proposed model show that the particle-phase concentration of DEHP at the chamber outlet reduces rapidly when the air flow rate is higher than 400 mL/min, the particles will go on sorbing/desorbing DEHP in the sampling trains downstream the chamber, smaller particles lead to a higher concentration of particle-phase DEHP in the chamber, and a larger chamber leads to a higher steady-state concentration but a slower process that the DEHP concentration reaches steady-state. Besides, there is a certain range for air flow rate in different chambers, e.g. 100–1000 mL/min in this study, to ensure the sorption of DEHP onto particles reaching the gas-/particle-phase equilibrium and reduce the errors induced by the deposition of particles.
Keywords: Air pollution; SVOCs transport; Airborne particle; Mathematical model; Residence time;

Recent improvement in air quality as evidenced by the island-wide monitoring network in Taiwan by Sheng-Po Chen; Chih-Chung Chang; Jyh-Jian Liu; Charles C.-K. Chou; Julius S. Chang; Jia-Lin Wang (70-77).
Long-term trends in total oxidants (O x , defined as NO2 + O3) and ozone (O3) were analyzed based on the annual averages calculated from 56 air-quality stations (AQS) across Taiwan from 1994 to 2012. A simple regression of the annual averages for the period from 1994 to 2012 revealed an increasing trend for O3 (+0.51 ppbv/yr) and relatively constant levels of O x at approximately 46 ppbv. However, when divided into two time periods, the O3 trend leveled off and remained constant at approximately 29 ppbv from 2007 to 2012, whereas the O x level drastically decreased (−0.66 ppbv/yr) during this same period. These recent changes in the O3 and O x trends island-wide were consistent with the trends observed in the largest metropolis, Taipei, suggesting a ubiquitous phenomenon. The changes in the O3 and O x trends around 2007 can be attributed to two causes from the observation point of view. As for the sink perspective, NO x levels have continued to decrease rapidly since 1994 (−0.82 ppbv/yr or −44% over 19 years), diminishing the NO-titration and, thus, increasing O3 levels, resulting in constant O x levels for the period prior to 2007. From the source perspective, continuous decreases in the levels of reducing agents (Non-methane hydrocarbons, NMHC: −0.012 ppmC/yr or −53% over 19 years, CO: −0.022 ppm/yr or −49% over 19 years) have lowered the photochemical O3 levels in recent years, resulting in altered O3 and O x levels after 2007. The oceanic baseline O3 averages revealed by AQS on the satellite islands around Taiwan also indicated consistent results in recent years, with O3 values notably lower (38–40 ppbv) than the peak values of 40–45 ppbv in the early 2000s.
Keywords: Ozone; Total oxidants; Long-term trend analysis;

Measured and modeled CO and NO y in DISCOVER-AQ: An evaluation of emissions and chemistry over the eastern US by Daniel C. Anderson; Christopher P. Loughner; Glenn Diskin; Andrew Weinheimer; Timothy P. Canty; Ross J. Salawitch; Helen M. Worden; Alan Fried; Tomas Mikoviny; Armin Wisthaler; Russell R. Dickerson (78-87).
Data collected during the 2011 DISCOVER-AQ field campaign in the Baltimore Washington region were used to evaluate CO and NO x emissions in the National Emissions Inventory (NEI). The average emissions ratio for the region was seen to be 11.2 ± 1.2 mol CO/mol NO x , 21% higher than that predicted by the NEI. Comparisons between in situ and remote observations and CMAQ model output show agreement in CO emissions of 15 ± 11% while NO x emissions are overestimated by 51–70% in Maryland. Satellite observations of CO by MOPITT show agreement with the Community Multiscale Air Quality (CMAQ) model within 3% over most of the eastern United States. CMAQ NO y mixing ratios were a factor of two higher than observations and result from a combination of errors in emissions and PAN and alkyl nitrate chemistry, as shown by comparison of three CMAQ model runs. Point source NO x emissions are monitored and agree with modeled emissions within 1% on a monthly basis. Because of this accuracy and the NEI assertion that approximately 3/4 of emissions in the Baltimore Washington region are from mobile sources, the MOVES model's treatment of emissions from aging vehicles should be investigated; the NEI overestimate of NO x emissions could indicate that engines produce less NO x and catalytic converters degrade more slowly than assumed by MOVES2010. The recently released 2011 NEI has an even lower CO/NO x emissions ratio than the projection used in this study; it overestimates NO x emissions by an even larger margin. The implications of these findings for US air quality policy are that NO x concentrations near areas of heavy traffic are overestimated and ozone production rates in these locations are slower than models indicate. Results also indicate that ambient ozone concentrations will respond more efficiently to NO x emissions controls but additional sources may need to be targeted for reductions.
Keywords: Air quality; National Emissions Inventory; CO; NO x ; On-road emissions; CMAQ;

Dispersion modeling of selected PAHs in urban air: A new approach combining dispersion model with GIS and passive air sampling by Ondřej Sáňka; Lisa Melymuk; Pavel Čupr; Alice Dvorská; Jana Klánová (88-95).
This study introduces a new combined air concentration measurement and modeling approach that we propose can be useful in medium and long term air quality assessment. A dispersion study was carried out for four high molecular weight polycyclic aromatic hydrocarbons (PAHs) in an urban area with industrial, traffic and domestic heating sources. A geographic information system (GIS) was used both for processing of input data as well as visualization of the modeling results. The outcomes of the dispersion model were compared to the results of passive air sampling (PAS). Despite discrepancies between measured and modeled concentrations, an approach combining the two techniques is promising for future air quality assessment. Differences between measured and modeled concentrations, in particular when measured values exceed the modeled concentrations, are indicative of undocumented, sporadic pollutant sources. Thus, these differences can also be useful for assessing and refining emission inventories.Display Omitted
Keywords: Passive air sampling; Air dispersion modeling; GIS; Polycyclic aromatic hydrocarbons; Emission inventories;

Reduced order modelling of an unstructured mesh air pollution model and application in 2D/3D urban street canyons by F. Fang; T. Zhang; D. Pavlidis; C.C. Pain; A.G. Buchan; I.M. Navon (96-106).
A novel reduced order model (ROM) based on proper orthogonal decomposition (POD) has been developed for a finite-element (FE) adaptive mesh air pollution model. A quadratic expansion of the non-linear terms is employed to ensure the method remained efficient. This is the first time such an approach has been applied to air pollution LES turbulent simulation through three dimensional landscapes. The novelty of this work also includes POD's application within a FE-LES turbulence model that uses adaptive resolution. The accuracy of the reduced order model is assessed and validated for a range of 2D and 3D urban street canyon flow problems. By comparing the POD solutions against the fine detail solutions obtained from the full FE model it is shown that the accuracy is maintained, where fine details of the air flows are captured, whilst the computational requirements are reduced. In the examples presented below the size of the reduced order models is reduced by factors up to 2400 in comparison to the full FE model while the CPU time is reduced by up to 98% of that required by the full model.
Keywords: Finite element; Proper orthogonal decomposition; Reduced order modelling; Air pollution;

Alkyl polycyclic aromatic hydrocarbons emissions in diesel/biodiesel exhaust by Carina S. Casal; Graciela Arbilla; Sergio M. Corrêa (107-116).
Polycyclic aromatic hydrocarbons (PAHs) are widely studied in environmental matrices, such as air, water, soil and sediment, because of their toxicity, mutagenicity and carcinogenicity. Because of these properties, the environmental agencies of developed countries have listed sixteen PAHs as priority pollutants. Few countries have limits for these compounds for ambient air, but they only limit emissions from stationary and mobile sources and occupational areas. There are several studies to specifically address the 16 priority PAHs and very little for the alkyl PAHs. These compounds are more abundant, more persistent and frequently more toxic than the non-alkylated PAHs, and the toxicity increases with the number of alkyl substitutions on the aromatic ring. In this study, a method was developed for the analysis of PAHs and alkyl PAHs by using a GC–MS and large injection volume injection coupled with program temperature vaporisation, which allows for limits of detection below 1.0 ng μL−1. Several variables were tested, such as the injection volume, injection velocity, injector initial temperature, duration of the solvent split and others. This method was evaluated in samples from particulate matter from the emissions of engines employing standard diesel, commercial diesel and biodiesel B20. Samples were collected on a dynamometer bench for a diesel engine cycle and the results ranged from 0.5 to 96.9 ng mL−1, indicating that diesel/biodiesel makes a significant contribution to the formation of PAHs and alkyl PAHs.
Keywords: Emission; Alkyl PAH; Diesel; Biodiesel; GC–MS;

Risk assessment of mortality for all-cause, ischemic heart disease, cardiopulmonary disease, and lung cancer due to the operation of the world's largest coal-fired power plant by Pei-Hsuan Kuo; Ben-Jei Tsuang; Chien-Jen Chen; Suh-Woan Hu; Chun-Ju Chiang; Jeng-Lin Tsai; Mei-Ling Tang; Guan-Jie Chen; Kai-Chen Ku (117-124).
Based on recent understanding of PM2.5 health-related problems from fossil-fueled power plants emission inventories collected in Taiwan, we have determined the loss of life expectancy (LLE) and the lifetime (75-year) risks for PM2.5 health-related mortalities as attributed to the operation of the world's largest coal-fired power plant; the Taichung Power Plant (TCP), with an installed nominal electrical capacity of 5780 MW in 2013. Five plausible scenarios (combinations of emission controls, fuel switch, and relocation) and two risk factors were considered. It is estimated that the lifetime (75-y) risk for all-cause mortality was 0.3%–0.6% for males and 0.2%–0.4% for females, and LLE at 84 days in 1997 for the 23 million residents of Taiwan. The risk has been reduced to one-fourth at 0.05%–0.10% for males and 0.03%–0.06% for females, and LLE at 15 days in 2007, which was mainly attributed to the installation of desulfurization and de-NO x equipment. Moreover, additional improvements can be expected if we can relocate the power plant to a downwind site on Taiwan, and convert the fuel source from coal to natural gas. The risk can be significantly reduced further to one-fiftieth at 0.001%–0.002% for males and 0.001% for females, and LLE at 0.3 days. Nonetheless, it is still an order higher than the commonly accepted elevated-cancer risk at 0.0001% (10−6), indicating that the PM2.5 health-related risk for operating such a world-class power plant is not negligible. In addition, this study finds that a better-chosen site (involving moving the plant to the leeward side of Taiwan) can reduce the risk significantly as opposed to solely transitioning the fuel source to natural gas. Note that the fuel cost of using natural gas (0.11 USD/kWh in 2013) in Taiwan is about twice the price of using coal fuel (0.05 USD/kWh in 2013).
Keywords: PM2.5; Mortality; Risk assessment; Life expectancy; Power plant;

A versatile and compact sampling system, the Sequential Spot Sampler (S3) has been developed for pre-concentrated, time-resolved, dry collection of fine and ultrafine particles. Using a temperature-moderated laminar flow water condensation method, ambient particles as small as 6 nm are deposited within a dry, 1-mm diameter spot. Sequential samples are collected on a multiwell plate. Chemical analyses are laboratory-based, but automated. The sample preparation, extraction and chemical analysis steps are all handled through a commercially-available, needle-based autosampler coupled to a liquid chromatography system. This automation is enabled by the small deposition area of the collection. The entire sample is extracted into 50–100 μL volume of solvent, providing quantifiable samples with small collected air volumes. A pair of S3 units was deployed in Stockton (CA) from November 2011 to February 2012. PM2.5 samples were collected every 12 h, and analyzed for polycyclic aromatic hydrocarbons (PAHs). In parallel, conventional filter samples were collected for 48 h and used to assess the new system's performance. An automated sample preparation and extraction was developed for samples collected using the S3. Collocated data from the two sequential spot samplers were highly correlated for all measured compounds, with a regression slope of 1.1 and r 2 = 0.9 for all measured concentrations. S3/filter ratios for the mean concentration of each individual PAH vary between 0.82 and 1.33, with the larger variability observed for the semivolatile components. Ratio for total PAH concentrations was 1.08. Total PAH concentrations showed similar temporal trend as ambient PM2.5 concentrations. Source apportionment analysis estimated a significant contribution of biomass burning to ambient PAH concentrations during winter.
Keywords: Sequential spot sampler; Time-resolved chemical speciation; Ambient particulate matter; Polycyclic aromatic hydrocarbons;

Proposed chemical mechanisms leading to secondary organic aerosol in the reactions of aliphatic amines with hydroxyl and nitrate radicals by Derek J. Price; Christopher H. Clark; Xiaochen Tang; David R. Cocker; Kathleen L. Purvis-Roberts; Philip J. Silva (135-144).
The presence and importance of amines in the atmosphere, including aliphatic amines, continues to gain more attention. The atmospheric reaction mechanisms of these amines with key atmospheric radicals are important to predict both daytime and nighttime atmospheric chemistry. While previous studies have focused on the production of amine salts, this analysis looks at the importance of peroxy radical reactions to the formation of secondary organic aerosol. Atmospheric oxidation mechanisms are presented to explain the observed chemistry. A series of environmental chamber experiments were conducted in which aliphatic tertiary and secondary amines were reacted with either hydroxyl radical (OH) or nitrate radical (NO3). Chemical composition of the aerosol products was obtained with a High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Particle Into Liquid Sampler Time of Flight Mass Spectrometer (PILS-ToF-MS), while the chemical composition of the gas-phase products was obtained with a Selected Ion Flow Tube Mass Spectrometer (SIFT-MS). A number of aerosol-phase mass spectra showed highly oxidized fragments at a much higher molecular weight (MW) than the amine precursor. It is proposed that these larger compounds are oligomers formed through peroxy radical reactions with hydrogen rearrangement. Another reaction pathway observed was the formation of amine salts. The relative importance of each pathway to the overall production of aerosol is found to be dependent on the type of amine and oxidant. For example, the oligomers were observed in the tertiary methyl amines, while the formation of amine salts was more prevalent in the secondary and tertiary ethyl amines.
Keywords: Peroxy radical; Amine; Oligomer formation; Mechanism; Mass spectrometry;

Atmospheric chemistry of HFE-7300 and HFE-7500: Temperature dependent kinetics, atmospheric lifetimes, infrared spectra and global warming potentials by Ana Rodríguez; Diana Rodríguez; Araceli Moraleda; Iván Bravo; Elena Moreno; Alberto Notario (145-153).
The atmospheric degradation of two hydrofluoroethers, HFE-7300 [n-C2F5CF(OCH3)CF(CF3)2] and HFE-7500 [n-C3F7CF(OC2H5)CF(CF3)2] used in industrial applications has been studied. The kinetics and reaction products were determined at atmospheric pressure as a function of temperature in a reaction chamber using GC/FID and GC/MS techniques for the analysis. The following Arrhenius expressions were obtained (in units of cm3 molecule−1 s−1): k HFE-7300 + OH = (5.6 ± 2.0) × 10−13 exp(−(1186 ± 111)/T); k HFE-7300 + Cl = (3.8 ± 1.3) × 10−12 exp(−(968 ± 101)/T); and k HFE-7500 + OH = (7.6 ± 6.0) × 10−12 exp(−(1163 ± 385)/T) (temperature range 271–333 K). The atmospheric lifetimes calculated from kinetic data for HFE-7300 and HFE-7500 were 5.24 and 0.30 years, respectively. In the oxidation of HFE-7300 with OH and Cl radicals, the only detected product was CF3CF2CF(OCHO)CF(CF3)2, whereas in the oxidation of HFE-7500 by OH radicals the detected products were: C3F7CF(OC(O)CH3)CF(CF3)2 and C3F7CF(OC(O)H)CF(CF3)2. Infrared spectra of the studied HFEs have also been measured and radiative forcing efficiencies were determined. Combining these results with the kinetic data, we estimated 100-year time horizon global warming potentials of 440 and 12 for HFE-7300 and HFE-7500, respectively.Display Omitted
Keywords: HFE-7300; HFE-7500; Atmospheric lifetimes; Reaction mechanism; Infrared spectra; Radiative efficiencies;

The keystone of this paper was to calculate and interpret indicators reflecting sources and air quality impacts of PM2.5 and PMCOARSE (PM10–PM2.5) in Rome (Italy), focusing on potential exogenous influences. A backward atmospheric trajectory cluster analysis was implemented. The likelihood of daily PM10 exceedances was studied in conjunction with atmospheric patterns, whereas a Potential Source Contribution Function (PSCF) based on air mass residence time was deployed on a grid of a 0.5° × 0.5° resolution. Higher PM2.5 concentrations were associated with short/medium range airflows originated from Balkan Peninsula, whereas potential PMCOARSE sources were localized across the Mediterranean and coastal North Africa, due to dust and sea spray transportation. According to the outcome of a daily Pollution Index (PI), a slightly increased degradation of air quality is induced due to the additional quantity of exogenous PM but nevertheless, average levels of PI in all trajectory clusters belong in the low pollution category. Gaseous and particulate pollutants were also elaborated by a Principal Component Analysis (PCA), which produced 4 components: [Traffic], [photochemical], [residential] and [Secondary Coarse Aerosol], reflecting local sources of air pollution. PM2.5 levels were strongly associated with traffic, whereas PMCOARSE were produced autonomously by secondary sources.
Keywords: PM10; PM2.5; Air mass trajectories; PSCF; Rome; Air quality;

Magnetic evaluation of TSP-filters for air quality monitoring by Ana Gabriela Castañeda-Miranda; Harald N. Böhnel; Roberto S. Molina-Garza; Marcos A.E. Chaparro (163-174).
We present the magnetic properties of the powders collected by high volume total suspended particle air samplers used to monitor atmospheric pollution in Santiago de Querétaro, a city of one million people in central Mexico. The magnetic measurements have been combined with scanning electron microscopy observations and analysis, in order to characterize the particles captured in the filters as natural and anthropogenic. The main goal of the study is to test if magnetic measurements on the sampled atmospheric dust can be effective, low-cost, proxy to qualitatively estimate the air quality, complementing the traditional analytical methods. The magnetic properties of the powder collected in the filters have been investigated measuring the low field magnetic susceptibility, hysteresis loops, thermomagnetic curves, and isothermal remanent magnetization. The rock magnetism data have been supplemented by energy-dispersive X-ray spectroscopy analysis and Raman spectroscopy. It was found that the main magnetic carrier is low-Ti magnetite in the PSD range with a contribution from SP particles, and small but significant contributions from hematite, maghemite and goethite particles. Total suspended particles in the atmosphere during the monitored days ranged between about 30 and 280 μg/m3. Magnetic susceptibility values are well correlated with the independently determined total suspended particles concentration (R = 0.93), but particle concentration does not correlate as well with IRM1T. This may be attributed to contributions from SP and paramagnetic particles to the susceptibility signal, but not to the remanence. The effects of climate in particle size, composition and concentration were considered in terms of precipitation and wind intensity, but they are actually minor. The main effect of climate appears to be the removal of SP particles during rainy days. There is a contribution to air pollution from natural mineral sources, which we attribute to low vegetation cover in the region's arid climate. The concentration of the magnetic particles and their grain-size vary according to the location of the monitoring station, with higher contributions to anthropogenic Fe-rich particles from vehicle emissions in the city center and other metals in the industrial parks. Metals of interest, usually diagnostic of atmospheric pollution (Fe, As, Sb, Cr, Mo, V, Zn, Ba, Pb, and Cu) were identified by means of electron microscopy.
Keywords: Environmental monitoring; Magnetic properties; Atmospheric pollution; Heavy metals; Anthropogenic airborne particles;

With over 6 million inhabitants the Houston metropolitan area is the fourth-largest in the United States. Ozone concentration in this southeast Texas region frequently exceeds the National Ambient Air Quality Standard (NAAQS). For this reason our study employed the Weather Research and Forecasting model with Chemistry (WRF/Chem) to quantify meteorological prediction differences produced by four widely used PBL schemes and analyzed its impact on ozone predictions. The model results were compared to observational data in order to identify one superior PBL scheme better suited for the area. The four PBL schemes include two first-order closure schemes, the Yonsei University (YSU) and the Asymmetric Convective Model version 2 (ACM2); as well as two turbulent kinetic energy closure schemes, the Mellor–Yamada–Janjic (MYJ) and Quasi-Normal Scale Elimination (QNSE). Four 24 h forecasts were performed, one for each PBL scheme. Simulated vertical profiles for temperature, potential temperature, relative humidity, water vapor mixing ratio, and the uv components of the wind were compared to measurements collected during the Second Texas Air Quality Study (TexAQS-II) Radical and Aerosol Measurements Project (TRAMP) experiment in summer 2006. Simulated ozone was compared against TRAMP data, and air quality stations from Continuous Monitoring Station (CAMS). Also, the evolutions of the PBL height and vertical mixing properties within the PBL for the four simulations were explored. Although the results yielded high correlation coefficients and small biases in almost all meteorological variables, the overall results did not indicate any preferred PBL scheme for the Houston case. However, for ozone prediction the YSU scheme showed greatest agreements with observed values.
Keywords: Planetary boundary layer; Atmospheric modeling; WRF/Chem; PBL parameterization;

Seasonal changes, identification and source apportionment of PAH in PM1.0 by Dayana Milena Agudelo-Castañeda; Elba Calesso Teixeira (186-200).
The objective of this research was to evaluate the seasonal variation of PAHs in PM1.0, as well as to identify and quantify the contributions of each source profile using the PMF receptor model. PM1.0 samples were collected on PTFE filters from August 2011 to July 2013 in the Metropolitan Area of Porto Alegre, Rio Grande do Sul, Brazil. The samples were extracted using the EPA method TO-13A and 16 Polycyclic Aromatic Hydrocarbons (PAHs) were analyzed using a gaseous chromatograph coupled with a mass spectrometer (GC–MS). Also, the data discussed in this study were analyzed to identify the relations of the PAHs concentrations with NOx, NO, O3 and meteorological parameters (temperature, solar radiation, wind speed, relative humidity). The results showed that in winter, concentrations of total PAHs were significantly higher than in summer, thus showing their seasonal variation. The identification of emission sources by applying diagnostic ratios confirmed that PAHs in the study area originate from mobile sources, especially, from diesel and gasoline emissions. The analysis by PMF receptor model showed the contribution of these two main sources of emissions, too, followed by coal combustion, incomplete combustion/unburned petroleum and wood combustion. The toxic equivalent factors were calculated to characterize the risk of cancer from PAH exposure to PM1.0 samples, and BaP and DahA dominated BaPeq levels.
Keywords: PAHs; PM1.0; PMF; Seasonal variation; Diagnostic ratios; Mobile sources; BaPeq;

The remarkable expansion of fertilization and irrigation may stimulate nitrous oxide (N2O) emissions from cropping systems in northern China. High-resolution measurements were conducted in irrigated cotton and wheat–maize rotational systems in Shanxi Province, P.R. China, between 2007 and 2010 (three year-round crop cycles, hereinafter referred to as Y1, Y2 and Y3) to investigate the impacts of natural inter-annual variations and agricultural management on annual N2O emissions and direct emission factors (EFs). Overall, N2O emissions fluctuated diurnally, seasonally and inter-annually in the fertilized treatments. The hourly N2O fluxes closely followed the daily air temperature patterns. The daily mean fluxes corresponded to these hourly fluxes, which were observed between 09:00–10:00 and 19:00–20:00. An optimized sampling protocol could improve the reliability of discrete measurements when estimating cumulative emissions. The N2O emissions for the fertilized treatments were 2.7 ± 0.2 (Y1) and 1.6 ± 0.1 kg N ha−1 yr−1 (Y2) from the cotton field and 6.2 ± 0.4 (Y1), 4.5 ± 0.3 (Y2) and 4.5 ± 0.2 kg N ha−1 yr−1 (Y3) from the wheat–maize field. Peak N2O emissions after fertilization and irrigation/rainfall lasted one to three weeks and accounted for 16–55% of the annual emissions. Leaching losses were estimated at 10.4 ± 3.0 (Y1) and 12.5 ± 3.4 kg N ha−1 yr−1 (Y2), which accounted for 16–17% of the fertilizer-N applied to the cotton field. Annual N2O emissions did not increase with increasing fertilization rates or water inputs because significant amounts of fertilizer-N were lost through leaching. Background emissions amounted to one-third to one-half of the total N2O emissions from the fertilized treatments. The direct EFs were 2.2 ± 0.3% (Y1) and 0.9 ± 0.2% (Y2) in the cotton field and 1.3 ± 0.2% (Y1), 0.8 ± 0.1% (Y2) and 0.7 ± 0.1% (Y3) in the wheat–maize field. The large inter-annual variations in N2O emissions and direct EFs emphasize the importance of multiple-year continuous observations.
Keywords: Nitrous oxide; Background emission; Direct emission factor; Irrigation; Leaching; Sampling protocol;

Impacts of biogenic isoprene emission on ozone air quality in the Seoul metropolitan area by Kwang-Yeon Lee; Kyung-Hwan Kwak; Young-Hee Ryu; Sang-Hyun Lee; Jong-Jin Baik (209-219).
The impacts of biogenic isoprene emission on ozone (O3) air quality during an episode under weak synoptic forcing in the Seoul metropolitan area (SMA), Republic of Korea, are investigated using the Community Multiscale Air Quality (CMAQ) modeling system coupled with the Weather Research and Forecasting (WRF) model. Simulations with different biogenic isoprene emission scenarios show that the impact of biogenic isoprene emission on the daily maximum O3 concentration is as high as 37 ppb in the Seoul region. The O3 concentration in the Seoul region is significantly increased by the biogenic isoprene emission from the surrounding region compared to that from within the Seoul region. In addition, the gas-phase chemistry is found to be the most important process for O3 concentration in the Seoul region in the presence of the biogenic isoprene emission from the surrounding region. While isoprene is not enough to influence O3 concentration directly due to its short lifetime, the transport of isoprene oxidation products plays a crucial role in increasing O3 concentration in the Seoul region. Through the process analysis, peroxy methacryloyl nitrate (MPAN) as well as formaldehyde (HCHO) and acetaldehyde (CCHO) is also identified as the important precursor that links biogenic isoprene emission from the surrounding region to O3 concentration in the Seoul region. After transported by daytime local circulations, the chemistry of isoprene oxidation products contributes to O3 formation in the Seoul region.
Keywords: Biogenic isoprene emission; Isoprene oxidation products; Ozone air quality; Seoul; WRF model; CMAQ modeling system;

Differences in CH4 and N2O emissions between rice nurseries in Chinese major rice cropping areas by Yi Zhang; Zhijie Li; Jinfei Feng; Xin Zhang; Yu Jiang; Jin Chen; Mingqian Zhang; Aixing Deng; Weijian Zhang (220-228).
Studies on greenhouse gas (GHG) emissions from paddy field have primarily focused on the post-transplanting period, however, recent researches raise new concerns about GHGs emission from rice nursery. In this study, CH4 and N2O fluxes were determined from different nurseries under major rice cropping systems in China. The tested nurseries included flooded nursery (FN), moist nursery (MN) and dry nursery (DN). Methane emissions from FN were significantly higher than those from MN and DN under all the rice cropping systems. When comparing with FN, MN decreased total CH4 emissions by 74.2%, 72.1% and 49.6% under the rice–upland rotation cropping system (RUR), and the double rice cropping system for the early rice (EDR) and the late rice (LDR), respectively. DN decreased CH4 emissions by 99.2%, 92.0%, 99.0% and 78.6% compared to FN under the single rice cropping system (SR), RUR, EDR and LDR, respectively. When comparing with FN, MN and DN increased N2O emissions by 58.1–134.1% and 28.2–332.7%, respectively. Ultimately, compared with FN across the cropping systems, MN and DN decreased net global warming potentials (GWPs) of CH4 and N2O by 33–68% and 43–86%, respectively. The mitigating effect of MN and DN on total GWPs varied greatly across the systems, ranging from 30.8% in the LDR to 86.5% in the SR. Chinese actual emission from rice nurseries was reduced to 956.66 × 103 t CO2 eq from the theoretical estimate of 2242.59 × 103 t CO2 eq if under the flooded nursery scenario in 2012. Taking into account the large rice nursery area (2032.52 × 103 ha) in China, the results of this study clearly indicate the importance to estimate and mitigate GHGs emission from flooded rice nursery. Being effective to reduce GHG emissions and increase rice yield, dry nursery technique is a promising candidate for climate smart rice cropping.
Keywords: Climate change; Greenhouse gas emissions; Global warming potential; Rice seedling nursery; Irrigation regime; Cropping systems;

Atmospheric degradation of saturated alcohols: Room temperature rate coefficients for NO3 radical reactions by Alberto Moreno; Sagrario Salgado; Raul Taccone; Pilar Martín; Beatriz Cabañas (229-235).
Rate coefficients for the reactions of NO3 radicals with a series of saturated alcohols are reported here using the relative rate technique. Experiments were performed using air as bath gas in a 50 L glass-pyrex reaction chamber at room temperature (298 ± 2) K with long-path FTIR spectroscopy used to monitor the reaction at atmospheric pressure (708 ± 8) Torr. The reference compounds used and their rate coefficients are: propanal k NO 3  = (6.0 ± 0.6) × 10−15, methyl methacrylate k NO 3  = (3.55 ± 0.62) × 10−15, acetaldehyde k NO 3  = (2.62 ± 0.29) × 10−15 and propene k NO 3  = (9.50 ± 1.9) × 10−15, in cm3 molecule−1 s−1. Rate coefficients obtained were (in units cm3 molecule−1 s−1): (1.87 ± 0.14) × 10−15, (2.39 ± 0.20) × 10−15, (2.28 ± 0.17) × 10−15, (1.80 ± 0.13) × 10−15 and (3.52 ± 0.19) × 10−15 for 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3,3-dimethyl-1-butanol and 3,3-dimethyl-2-butanol respectively. Reactivity trend can be explained in terms of the different types of hydrogen inside the hydrocarbon chain. The reaction occurs by an initial H-atom abstraction mainly from C–H groups of the alcohols by the NO3 radical being NO3 more reactive towards an H atom attached to a tertiary carbon than that attached to a secondary or primary carbon. Reactivity trend is compared with their similar structural 2-butanol and with the corresponding alkanes. Atmospheric implications are also discussed calculating lifetimes of the saturated alcohols studied here due to the reaction with NO3 radicals in comparison to their reactions with the other major atmospheric oxidants.
Keywords: Atmospheric chemistry; Saturated alcohols; Rate coefficients; Relative technique; FTIR detection method;

Natural near field sinks of hydrogen sulfide from two geothermal power plants in Iceland by S. Olafsdottir; S.M. Gardarsson; H.O. Andradottir (236-244).
Hydrogen sulfide (H2S) emissions have been growing with the increasing utilization of geothermal resources. Atmospheric H2S concentration has been measured and studied but less is known about the natural sinks of the chemical. This study investigates the atmospheric depletion of H2S within a 35 km distance from two Icelandic power plants. The results showed that atmospheric oxidation by the OH radical was the largest sink in the area. The second largest sink was H2S uptake in surface water, in a neighboring lake, but it was, however, small compared to the reported difference of sulfur amount in the lake in- and outflow. Sulfur was found to accumulate in moss close to the power plants at a maximum rate of about 1500 mg S/kg moss per year and decreased exponentially from the source, being negligible at a distance of a few kilometers. Soil uptake was limited by diffusion of H2S into the porous media and was thus much smaller than the estimated soil uptake potential. Washout with precipitation was estimated to be the smallest sink due to the low H2S reactivity in the precipitation (pH = 5.6), compared to the surface water (pH ∼8). Depletion of H2S from the atmosphere in the study area was estimated to be about 1.2% of the 2012 power plants emissions of over 20,000 tons. Although the uncertainties in the depletion estimates were considerable, most of the H2S emitted from the power plants was strongly indicated to be transported out of the study area as H2S.
Keywords: Hydrogen sulfide; Atmospheric sinks; Geothermal emission; Near field fate;

Pollution patterns in the upper troposphere over Europe and Asia observed by CARIBIC by Angela K. Baker; Sebastian Traud; Carl A.M. Brenninkmeijer; Peter Hoor; Marco Neumaier; David E. Oram; Armin Rauthe-Schöch; Detlev Sprung; Sebastian Schloegl; Franz Slemr; Peter F.J. van Velthoven; Heini Wernli; Andreas Zahn; Helmut Ziereis (245-256).
Between May 2005 and March 2008 the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) observatory was deployed to make atmospheric observations on 42 flights between Frankfurt, Germany and Manila, the Philippines. This nearly 3 year flight series provides information about atmospheric composition in the upper troposphere over Europe and Asia during all seasons and was used to investigate seasonal and regional differences in trace gas distributions and the influence of long range transport and local convection on composition. The flight route was separated into three different regions having characteristic differences in transport and composition; these were Europe and Western Asia (5°E–60°E), Central Asia (60°E–100°E) and Southeast Asia (100°E–125°E). The region over Europe and Western Asia was strongly influenced by air masses from North America, while the region over Southeast Asia was mostly influenced by local emissions, particularly from biomass/biofuel burning as indicated by high levels of acetonitrile and carbon monoxide. Air masses over Central Asia were found to be influenced by both recent convection from the Indian subcontinent and mid-range transport from Europe, Western Asia and the Middle East. Elevated levels of propane and other non-methane hydrocarbons, both with and without concomitant elevations in other trace gases (i.e. carbon monoxide, acetonitrile) was a persistent feature over Central Asia in all seasons except summer, and were particularly prominent in fall. Influences on composition over Central Asia were investigated in detail for a case study from a series of flights in October 2006, where elevated levels of pollutants were found to be the result of convective transport of both biomass/biofuel burning and urban emissions from South Asia and fossil fuel related emissions from Eastern Europe.
Keywords: Asian pollution; Upper troposphere; Airborne measurements; Long-range transport; Convection;

A case-crossover analysis of forest fire haze events and mortality in Malaysia by Mazrura Sahani; Nurul Ashikin Zainon; Wan Rozita Wan Mahiyuddin; Mohd Talib Latif; Rozita Hod; Md Firoz Khan; Norhayati Mohd Tahir; Chang-Chuan Chan (257-265).
The Southeast Asian (SEA) haze events due to forest fires are recurrent and affect Malaysia, particularly the Klang Valley region. The aim of this study is to examine the risk of haze days due to biomass burning in Southeast Asia on daily mortality in the Klang Valley region between 2000 and 2007. We used a case-crossover study design to model the effect of haze based on PM10 concentration to the daily mortality. The time-stratified control sampling approach was used, adjusted for particulate matter (PM10) concentrations, time trends and meteorological influences. Based on time series analysis of PM10 and backward trajectory analysis, haze days were defined when daily PM10 concentration exceeded 100 μg/m3. The results showed a total of 88 haze days were identified in the Klang Valley region during the study period. A total of 126,822 cases of death were recorded for natural mortality where respiratory mortality represented 8.56% (N = 10,854). Haze events were found to be significantly associated with natural and respiratory mortality at various lags. For natural mortality, haze events at lagged 2 showed significant association with children less than 14 years old (Odd Ratio (OR) = 1.41; 95% Confidence Interval (CI) = 1.01–1.99). Respiratory mortality was significantly associated with haze events for all ages at lagged 0 (OR = 1.19; 95% CI = 1.02–1.40). Age-and-gender-specific analysis showed an incremental risk of respiratory mortality among all males and elderly males above 60 years old at lagged 0 (OR = 1.34; 95% CI = 1.09–1.64 and OR = 1.41; 95% CI = 1.09–1.84 respectively). Adult females aged 15–59 years old were found to be at highest risk of respiratory mortality at lagged 5 (OR = 1.66; 95% CI = 1.03–1.99). This study clearly indicates that exposure to haze events showed immediate and delayed effects on mortality.
Keywords: Air pollution; Haze; PM10; Case-crossover; Mortality; Malaysia;

Some sources may need to estimate ozone and secondarily formed PM2.5 as part of the permit application process under the Clean Air Act New Source Review program. Photochemical grid models represent state-of-the-science gas- and particle-phase chemistry and provide a realistic chemical and physical environment for assessing changes in air quality resulting from changes in emissions. When using these tools for single source impact assessments, it is important to differentiate a single source impact from other emissions sources and to understand how well contemporary grid model applications capture near-source transport and chemistry. Here for the first time, both source apportionment and source sensitivity approaches (brute-force changes and high-order direct decoupled method) are used in a photochemical grid model to isolate impacts of a specific facility. These single source impacts are compared with in-plume measurements made as part of a well-characterized 1999 TVA Cumberland aircraft plume transect field study. The techniques were able to isolate the impacts of the TVA plume in a manner consistent with observations. The model predicted in-plume concentrations well when the observations were averaged to the grid scale, although peak concentrations of primary pollutants were generally underestimated near the source, possibly due to dilution in the 4-km grid cell.
Keywords: Photochemical model; Plume; Ozone; PM; Single source; Source apportionment;

Spatio-temporal variation of urban ultrafine particle number concentrations by Martina S. Ragettli; Regina E. Ducret-Stich; Maria Foraster; Xavier Morelli; Inmaculada Aguilera; Xavier Basagaña; Elisabetta Corradi; Alex Ineichen; Ming-Yi Tsai; Nicole Probst-Hensch; Marcela Rivera; Rémy Slama; Nino Künzli; Harish C. Phuleria (275-283).
Methods are needed to characterize short-term exposure to ultrafine particle number concentrations (UFP) for epidemiological studies on the health effects of traffic-related UFP. Our aims were to assess season-specific spatial variation of short-term (20-min) UFP within the city of Basel, Switzerland, and to develop hybrid models for predicting short-term median and mean UFP levels on sidewalks. We collected measurements of UFP for periods of 20 min (MiniDiSC particle counter) and determined traffic volume along sidewalks at 60 locations across the city, during non-rush hours in three seasons. For each monitoring location, detailed spatial characteristics were locally recorded and potential predictor variables were derived from geographic information systems (GIS). We built multivariate regression models to predict local UFP, using concurrent UFP levels measured at a suburban background station, and combinations of meteorological, temporal, GIS and observed site characteristic variables. For a subset of sites, we assessed the relationship between UFP measured on the sidewalk and at the nearby residence (i.e., home outdoor exposure on e.g. balconies). The average median 20-min UFP levels at street and urban background sites were 14,700 ± 9100 particles cm−3 and 9900 ± 8600 particles cm−3, respectively, with the highest levels occurring in winter and the lowest in summer. The most important predictor for all models was the suburban background UFP concentration, explaining 50% and 38% of the variability of the median and mean, respectively. While the models with GIS-derived variables (R 2 = 0.61) or observed site characteristics (R 2 = 0.63) predicted median UFP levels equally well, mean UFP predictions using only site characteristic variables (R 2 = 0.62) showed a better fit than models using only GIS variables (R 2 = 0.55). The best model performance was obtained by using a combination of GIS-derived variables and locally observed site characteristics (median: R 2 = 0.66; mean: R 2 = 0.65). The 20-min UFP concentrations measured at the sidewalk were strongly related (R 2 = 0.8) to the concurrent 20-min residential UFP levels nearby. Our results indicate that median UFP can be moderately predicted by means of a suburban background site and GIS-derived traffic and land use variables. In areas and regions where large-scale GIS data are not available, the spatial distribution of traffic-related UFP may be assessed reasonably well by collecting on-site short-term traffic and land-use data.
Keywords: Nanoparticles; Exposure assessment; Traffic; Monitoring; Short-term exposure; Switzerland;

Estimating North American background ozone in U.S. surface air with two independent global models: Variability, uncertainties, and recommendations by A.M. Fiore; J.T. Oberman; M.Y. Lin; L. Zhang; O.E. Clifton; D.J. Jacob; V. Naik; L.W. Horowitz; J.P. Pinto; G.P. Milly (284-300).
Accurate estimates for North American background (NAB) ozone (O3) in surface air over the United States are needed for setting and implementing an attainable national O3 standard. These estimates rely on simulations with atmospheric chemistry-transport models that set North American anthropogenic emissions to zero, and to date have relied heavily on one global model. We examine NAB estimates for spring and summer 2006 with two independent global models (GEOS-Chem and GFDL AM3). We evaluate the base simulations, which include North American anthropogenic emissions, with mid-tropospheric O3 retrieved from space and ground-level O3 measurements. The models often bracket the observed values, implying value in developing a multi-model approach to estimate NAB O3. Consistent with earlier studies, the models robustly simulate the largest nation-wide NAB levels at high-altitude western U.S. sites (seasonal average maximum daily 8-h values of ∼40–50 ppb in spring and ∼25–40 ppb in summer) where it correlates with observed O3. At these sites, a 27-year GFDL AM3 simulation simulates observed O3 events above 60 ppb and indicates that year-to-year variations in NAB O3 influence their annual frequency (with NAB contributing 50–60 ppb or more during individual events). During summer over the eastern United States (EUS), when photochemical production from regional anthropogenic emissions peaks, NAB is largely uncorrelated with observed values and it is lower than at high-altitude sites (average values of ∼20–30 ppb). Four processes contribute substantially to model differences in specific regions and seasons: lightning NO x , biogenic isoprene emissions and chemistry, wildfires, and stratosphere-to-troposphere transport. Differences in the representations of these processes within the GFDL AM3 and GEOS-Chem models contribute more to uncertainty in NAB estimates, particularly in spring when NAB is highest, than the choice of horizontal resolution within a single model (GEOS-Chem). We propose that future efforts seek to constrain these processes with targeted analysis of multi-model simulations evaluated with observations of O3 and related species from multiple platforms, and thereby reduce the error on NAB estimates needed for air quality planning.
Keywords: Surface ozone; Background ozone; Air pollution; Air quality; Exceptional events;

Field measurement of nitromethane from automotive emissions at a busy intersection using proton-transfer-reaction mass spectrometry by Satoshi Inomata; Yuji Fujitani; Akihiro Fushimi; Hiroshi Tanimoto; Kanako Sekimoto; Hiroyuki Yamada (301-309).
Field measurements of seven nitro-organic compounds including nitromethane and ten related volatile organic compounds were carried out using proton-transfer-reaction mass spectrometry at a busy intersection of an urban city, Kawasaki, Japan from 26th February to 6th March, 2011. Among the nitro-organic compounds, nitromethane was usually observed along with air pollutants emitted from automobiles. The mixing ratios of nitromethane varied substantially and sometimes clearly varied at an approximately constant interval. The interval corresponded to the cycle of the traffic signals at the intersection and the regular peaks of nitromethane concentrations were caused by emissions from diesel trucks running with high speed. In addition to the regular peaks, sharp increases of nitromethane concentrations were often observed irregularly from diesel trucks accelerating in front of the measurement site. For other nitro-organic compounds such as nitrophenol, nitrocresol, dihydroxynitrobenzene, nitrobenzene, nitrotoluene, and nitronaphthalene, most of the data fluctuated within the detection limits.
Keywords: Diesel vehicle; Exhaust gas; Nitromethane; Nitro-organic compounds; Proton-transfer-reaction mass spectrometry;

A carbon number-functionality grid (CNFG) for a complex mixture of secondary organic aerosol (SOA) precursors and oxidation products was developed from the theoretical retention index diagram of a multidimensional gas chromatographic (GC × 2GC) analysis of a mixture of SOA precursors and derivatized oxidation products. In the GC × 2GC analysis, comprehensive separation of the complex mixture was achieved by diverting the modulated effluent from a polar primary column into 2 polar secondary columns. Column stationary phases spanned the widest range of selectivity of commercially available GC analytic columns. In general, separation of the species by the polar primary column was by the number of carbon atoms in the molecule (when the homologous series of reference compounds was selected to have molecular volumes and functionalities similar to the target analytes) and the polar secondary columns provided additional separation according to functionality. An algebraic transformation of the Abraham solvation parameter model was used to estimate linear retention indices of solutes relative to elution of a homologous series of methyl diesters on the primary and secondary columns to develop the theoretical GC × 2GC retention diagram. Retention indices of many of the oxidation products of SOA precursors were estimated for derivatized forms of the solutes. The GC stationary phases selected for the primary column [(50%-Trifluoropropyl)-methylpolysiloxane] and secondary columns (90% Cyanopropyl Polysilphenylene-siloxane and Polyethylene Glycol in a Sol-Gel matrix) provided a theoretical separation of 33 SOA precursors and 98 derivatized oxidation products into 35 groups by molecular volume and functionality. Comprehensive analysis of extracts of vapor and aerosol samples containing semivolatile SOA precursors and oxidation products, respectively, is best accomplished by (1) separating the complex mixture of the vapor and underivatized aerosol extracts with a (50%-Trifluoropropyl)-methylpolysiloxane × 90% Cyanopropyl Polysilphenylene-siloxane × Polyethylene Glycol in a Sol-Gel matrix arrangement and (2) derivatizing the aerosol extract and reanalyzing the sample on the GC × 2GC column combination. Quantifying groupings and organic molecular species in time series of collections of vapor- and aerosol-phase atmospheric organic matter is a promising analytic technique for measuring production of SOA and evaluating transformations of SOA precursors.
Keywords: Aerosol life cycle; GC × 2GC; Multidimensional gas chromatography; Secondary organic aerosol; Semivolatile SOA precursors; Solvation parameter model;

New screening approach for risk assessment of pesticides in ambient air by Vicent Yusà; Clara Coscollà; Maurice Millet (322-330).
We present a novel screening approach for inhalation risk assessment of currently used pesticides (CUPs) in ambient air, based on the measurements of pesticide levels in the inhalable fraction of the particulate matter (PM10). Total concentrations in ambient air (gas + particle phases) were estimated using a theoretical model of distribution of semi-volatile organic compounds between the gas and the particulate phase based on the octanol–air partition (K oa) of each pesticide. The proposed approach was used in a pilot study conducted in a rural station in Valencia (Spain) from April through to October 2010. Twenty out of 82 analysed pesticides were detected in average concentrations ranging from 1.63 to 117.01 pg m−3. For adults, children and infants the estimated chronic inhalation risk, expressed as Hazard Quotient (HQ) was <1 for all pesticides. Likewise, the cumulative exposure for detected organophosphorus, pyrethroids and carbamates pesticides, was estimated using as metrics the Hazard Index (HI), which was less than 1 for the three families of pesticides assessed. The cancer risk estimated for the detected pesticides classified as Likely or Possible carcinogens was less than 1.15E-7 for infants. In our opinion, the screening approach proposed could be used in the monitoring and risk assessment of pesticides in ambient air.Display Omitted
Keywords: Pesticides; Exposure assessment; Risk assessment; Inhalation; Gas/particle partitioning;

The new generation of secondary organic aerosol (SOA) models that represent gas- and particle-phase chemistry and thermodynamic partitioning using discrete two-dimensional grids (e.g. SOM, 2D-VBS) cannot be efficiently implemented into three-dimensional atmospheric chemical transport models (CTMs) due to the large number of bins (tracers) required. In this study, we introduce a novel mathematical framework, termed the Oxidation State/Volatility Moment Method, that is designed to address these computational burdens so as to allow the new generation of SOA models to be implemented into CTMs. This is accomplished by mapping the two-dimensional grids onto probability distributions that conserve carbon and oxygen mass. Assessment of the Moment Method strengths (speed, carbon and oxygen conservation) and weaknesses (numerical drift) provide valuable insight that can guide future development of SOA modules for atmospheric CTMs.
Keywords: Secondary organic aerosol; 2-Dimensional SOA model; Chemical transport model; Probability distribution; Computational efficiency;

Modeling global persistent organic chemicals in clouds by Xiaoxuan Mao; Hong Gao; Tao Huang; Lisheng Zhang; Jianmin Ma (345-352).
A cloud model was implemented in a global atmospheric transport model to simulate cloud liquid water content and quantify the influence of clouds on gas/aqueous phase partitioning of persistent organic chemicals (POCs). Partitioning fractions of gas/aqueous and particle phases in clouds for three POCs α-hexachlorocyclohexane (α-HCH), polychlorinated biphenyl-28 (PCB-28), and PCB-138 in a cloudy atmosphere were estimated. Results show that the partition fraction of these selected chemicals depend on cloud liquid water content (LWC) and air temperature. We calculated global distribution of water droplet/ice particle–air partitioning coefficients of the three chemicals in clouds. The partition fractions at selected model grids in the Northern Hemisphere show that α-HCH, a hydrophilic chemical, is sorbed strongly onto cloud water droplets. The computed partition fractions at four selected model grids show that α-HCH tends to be sorbed onto clouds over land (source region) from summer to early fall, and over ocean from late spring to early fall. 20–60% of α-HCH is able to be sorbed to cloud waters over mid-latitude oceans during summer days. PCB-138, one of hydrophobic POCs, on the other hand, tends to be sorbed to particles in the atmosphere subject to air temperature. We also show that, on seasonal or annual average, 10–20% of averaged PCB-28 over the Northern Hemisphere could be sorbed onto clouds, leading to reduction of its gas-phase concentration in the atmosphere.
Keywords: Clouds; Persistent organic chemicals; Atmospheric partition; Long-range atmospheric transport;

Deviations from the O3–NO–NO2 photo-stationary state in Delhi, India by Dilip M. Chate; Sachin D. Ghude; Gurfan Beig; Anoop S. Mahajan; Chinmay Jena; Reka Srinivas; Anita Dahiya; Nandini Kumar (353-358).
A network of air quality and weather monitoring stations was set-up across Delhi, India, under the System of Air quality Forecasting And Research (SAFAR) project. The objective of this network was to enable better understanding of air quality in terms of atmospheric chemistry, emissions and forecasting in Delhi, one of the largest metropolises in the world. In this study, we focus on the O3–NO–NO2-triad Photo Stationary State (PSS), and investigate site-specific deviations in the Leighton Ratio (Φ) during a short period in 2012 (1–31 December). Large variations were observed in the NO (<1 ppbv to a peak of 295 ppbv), NO2 (<2 ppbv–47 ppbv) and O3 (4 ppbv–95 ppbv) mixing ratios, all of which showed strong diurnal variation. The Φ values showed large deviations from unity over the measurement period, with mostly negative deviations (Φ < 1), showing that the air masses were dominated by local sources of NO x and that the PSS was not achieved. Positive deviations (Φ > 1) were also observed occasionally, and these data were used to estimate the total peroxy radical (PO2) mixing ratios. This is the first estimate of PO2 reported for the city of Delhi and compares well with the results in the literature.
Keywords: Photo-stationary state; Leighton ratio; Ozone; Nitrogen oxides; SAFAR;

Continuous particle number size distributions (15 nm–2.5 μm), particle chemical compositions, gaseous species and meteorological variables were collected at an urban site in Beijing to investigate the source apportionment of ambient fine particle number concentrations. Hourly data sets were analyzed using the positive matrix factorisation (PMF) which identified a total of eight factors: two traffic factors, two combustion factors, secondary nitrate factors, secondary sulfate + secondary organic aerosol (SOA), fugitive dust and regionally transported aerosol. Traffic (47.9%) and combustion (29.7%) aerosol were found to dominate the particle number concentrations, whereas the most important sources for particle volume concentrations were found to be regionally transported aerosol (30.9%) and combustions (30.1%). Although the diurnal pattern of each of the two traffic factors closely followed traffic rush hour for Beijing, their size modes were different suggesting that these factors might represent local and remote emissions. Biomass burning and coal-fired power plant aerosol were distinguished according to their size modes and chemical species associated with them. Secondary compounds showed similar bimodal particle number size distribution, the distinct diurnal pattern distinguished these factors as secondary nitrate and mixed source of secondary sulfate and SOA. Regionally transported material was characterized by accumulation mode particles. Overall, the introduction of combinations of particle number size distributions and chemical composition data in PMF model is successful at separating the components and quantifying relative contributions to the particle number and volume size distributions in the complex urban atmosphere.
Keywords: Number size distribution; Chemical composition; Positive matrix factorization; Source apportionment; Fine particle;

Observations of new particle formation at two distinct Indian subcontinental urban locations by V.P. Kanawade; Sachchida N. Tripathi; Devendraa Siingh; Alok S. Gautam; Atul K. Srivastava; Adarsh K. Kamra; Vijay K. Soni; Virendra Sethi (370-379).
While the formation of new atmospheric aerosol particles and their subsequent growth have been observed under diverse environmental conditions globally, such observations are very scarce over Indian subcontinent. Here, we present the systematic analysis for new particle formation (NPF) from two distinct urban locations in India during April–May of two consecutive years. Particle size distributions were measured at Pune (18.53°N, 73.85°E) during 16 April–23 May, 2012 and at Kanpur (26.46°N, 80.32°E) during 16 April–23 May, 2013. The campaign mean total particle number concentration in the similar size range of 4–135 nm at Pune (12.2 × 103 cm−3) was higher than at Kanpur (7.9 × 103 cm−3), whereas the estimated total condensation sink (CS 4–750) at Pune (16.2 × 10−3 s−1) was lower than at Kanpur (33.3 × 10−3 s−1). Despite lower particle number concentrations at Kanpur, larger particle sizes resulted in higher condensation sink than at Pune. The mean particle mode diameter at Kanpur was found larger by a factor of ∼1.8 than at Pune. NPF events were observed commonly at both sites, with lower frequency at Kanpur (14%) than that at Pune (26%). The derived particle growth rates, GR, and the formation rates of 5 nm particles, J 5, ranged from 3.4 to 13.3 nm h−1 and 0.4 to 13.9 cm−3 s−1, respectively, which are generally comparable to typical values reported in previous studies. Generally, the particle growth rates were found higher at Kanpur, whereas the formation rates were higher at Pune. It appears that the presence of pre-existing large particles at Kanpur than at Pune suppressed formation rates and favored particle growth. Overall, NPF occurred at lower condensation sink, lower RH, higher solar radiation, and higher temperature.
Keywords: Particle size distribution; Ultrafine particles; Formation rate; Growth; Urban;

A new dust transport approach to quantify anthropogenic sources of atmospheric PM10 deposition on lakes by Lee Weiss; Jesse Thé; Bahram Gharabaghi; Eleanor A. Stainsby; Jennifer G. Winter (380-392).
Windblown dust simulations are one of the most uncertain types of atmospheric transport models. This study presents an integrated PM10 emission, transport and deposition model which has been validated using monitored data. This model characterizes the atmospheric phosphorus load focusing on the major local sources within the Lake Simcoe airshed including paved and unpaved roads, agricultural sources, construction sites and aggregate mining sources. This new approach substantially reduces uncertainty by providing improved estimates of the friction velocities than those developed previously. Modeling improvements were also made by generating and validating an hourly windfield using detailed meteorology, topography and land use data for the study area. The model was used to estimate dust emissions generated in the airshed and to simulate the long-range transport and deposition of PM10 to Lake Simcoe. The deposition results from the model were verified against observed bulk collector phosphorus concentration data for both wet and dry deposition. Bulk collector data from stations situated outside the airshed in a remote, undeveloped area were also compared to determine the background contribution from distant sources.
Keywords: Dust emissions; Lake Simcoe; Phosphorus; Deposition; Dust model;

Physicochemical characterization of aged biomass burning aerosol after long-range transport to Greece from large scale wildfires in Russia and surrounding regions, Summer 2010 by E. Diapouli; O. Popovicheva; M. Kistler; S. Vratolis; N. Persiantseva; M. Timofeev; A. Kasper-Giebl; K. Eleftheriadis (393-404).
Smoke aerosol emitted by large scale wildfires in the European part of Russia and Ukraine, was transported to Athens, Greece during August 2010 and detected at an urban background site. Measurements were conducted for physico-chemical characterization of the aged aerosol and included on-line monitoring of PM10 and carbonaceous particles mass concentrations, as well as number size distributions and aerosol optical properties. In addition TSP filter samples were analyzed for major inorganic ions, while morphology and composition of particles was studied by individual particle analysis. Results supported the long-range transport of smoke plumes from Ukraine and Russia burning areas indicated by back trajectory analysis. An increase of 50% and 40% on average in organic (OC) and elemental carbon (EC) concentrations respectively, and more than 95% in carbonate carbon (CC) levels was observed for the biomass burning (BB) transport period of August with respect to the previous month of July. Mean 24-h OC/EC ratio was found in the range 3.2–8.5. Single scattering albedo (SSA) was also increased, indicating abundance of light scattering constituents and/or shift of size distributions towards larger particles. Increase in particle size was further supported by a decreasing trend in absorption Angström exponent (AAE). Ion analysis showed major contribution of secondary species (ammonium sulfate and nitrate) and soil components (Ca2+, Mg2+). Non-sea salt K+ exhibited very good correlation with secondary species, indicating the long-range transport of BB smoke as a possible common source. Individual particle analysis of the samples collected during BB-transport event in Athens revealed elevated number of soot externally mixed with fly ash Ca-rich particles. This result is in agreement with the increased OC and CC levels measured, thus pointing towards the main components comprising the aged BB aerosol microstructure.Display Omitted
Keywords: Wildfires event; Long-range transport; Aged biomass burning aerosol; Chemical speciation; Individual particle analysis; Optical properties;

Physicochemical characterization of smoke aerosol during large-scale wildfires: Extreme event of August 2010 in Moscow by O. Popovicheva; M. Kistler; E. Kireeva; N. Persiantseva; M. Timofeev; V. Kopeikin; A. Kasper-Giebl (405-414).
Enhancement of biomass burning-related research is essential for the assessment of large-scale wildfires impact on pollution at regional and global scale. Starting since 6 August 2010 Moscow was covered with thick smoke of unusually high PM10 and BC concentrations, considerably affected by huge forest and peat fires around megacity. This work presents the first comprehensive physico-chemical characterization of aerosols during extreme smoke event in Moscow in August 2010. Sampling was performed in the Moscow center and suburb as well as one year later, in August 2011 during a period when no biomass burning was observed. Small-scale experimental fires of regional biomass were conducted in the Moscow region. Carbon content, functionalities of organic/inorganic compounds, tracers of biomass burning (anhydrosaccharides), ionic composition, and structure of smoke were analyzed by thermal-optical analysis, FTIR spectroscopy, liquid and ion chromatography, and electron microscopy. Carbonaceous aerosol in August 2010 was dominated by organic species with elemental carbon (EC) as minor component. High average OC/EC near 27.4 is found, comparable to smoke of regional biomass smoldering fire, and exceeded 3 times the value observed in August 2011. Organic functionalities of Moscow smoke aerosols were hydroxyl, aliphatic, aromatic, acid and non-acid carbonyl, and nitro compound groups, almost all of them indicate wildfires around city as the source of smoke. The ratio of levoglucosan (LG) to mannosan near 5 confirms the origin of smoke from coniferous forest fires around megacity. Low ratio of LG/OC near 0.8% indicates the degradation of major molecular tracer of biomass burning in urban environment. Total concentration of inorganic ions dominated by sulfates SO 4 2 − and ammonium NH 4 + was found about 5 times higher during large-scale wildfires than in August 2011. Together with strong sulfate and ammonium absorbance in smoke aerosols, these observations prove the formation of secondary inorganic species associated with wildfire gaseous emissions and their transformation in aged smoke. Accumulation of carbonyl compounds during extreme smoke event in Moscow resulted from photochemical aging and secondary organic aerosol (SOA) formation in the urban atmosphere. The mixture of carbonaceous particles and dust revealed multicomponent structure of Moscow smoke aerosols, pointing the difference with non-smoke ambient aerosols. The abundance of group containing soot and tar balls approached at least a half of total aerosol concentration during extreme event, relating to elevated OC, EC and SOA. Fly ash groups contained calcium sulfates and carbonates from soil entrainment by hot air convection. Small-scale open fire experiments support the identification of specific chemical features of regional biomass burning and demonstrate the strong impact of large-scale wildfires on aerosol chemistry and air quality in highly polluted megacity.Display Omitted
Keywords: Smoke event; Biomass burning; Physico-chemical characterization; Aerosol chemistry; Multicomponent smoke structure;

Soil and biomass mercury emissions during a prescribed fire in the Amazonian rain forest by Jose J. Melendez-Perez; Anne H. Fostier; João A. Carvalho; Claudia C. Windmöller; José C. Santos; Anthony Carpi (415-422).
Mercury stored in forests can be volatilized to the atmosphere during fires. Many factors influence this process such as mercury concentration, vegetation loading and the soil temperature reached during the fire. We quantified mercury emissions from biomass and soil during a prescribed fire in Brazil using the difference in mercury burden in vegetation and soil before and after burning, and data were critically compared with those previously obtained in a similar experiment in another part of the Amazonia. The calculated mercury emission factor was 4.1 ± 1.4 g Hg ha−1, with the main part (78%) originating from litterfall and O-horizon, and only 14% associated with live biomass. When considering the fuel burned loading, the emission factor ranged from 40 to 53 μg Hg kg−1. Data were also obtained on soil temperature profile and on Hg speciation in soil in an effort to relate these parameters to Hg emissions.Display Omitted
Keywords: Forest fire; Mercury emissions; Amazon;

Gaseous mercury emissions from soil following forest loss and land use changes: Field experiments in the United States and Brazil by Anthony Carpi; Anne H. Fostier; Olivia R. Orta; Jose Carlos dos Santos; Michael Gittings (423-429).
Forest ecosystems are a sink of atmospheric mercury, trapping the metal in the canopy, and storing it in the forest floor after litter fall. Fire liberates a portion of this mercury; however, little is known about the long-term release of mercury post deforestation. We conducted two large-scale experiments to study this phenomenon. In upstate New York, gaseous mercury emissions from soil were monitored continually using a Teflon dynamic surface flux chamber for two-weeks before and after cutting of the canopy on the edge of a deciduous forest. In Brazil, gaseous mercury emissions from soil were monitored in an intact Ombrophilous Open forest and an adjacent field site both before and after the field site was cleared by burning. In the intact forest, gaseous mercury emissions from soil averaged −0.73 ± 1.84 ng m−2 h−1 (24-h monitoring) at the New York site, and 0.33 ± 0.09 ng m−2 h−1 (daytime-only) at the Brazil site. After deforestation, gaseous mercury emissions from soil averaged 9.13 ± 2.08 ng m−2 h−1 in New York and 21.2 ± 0.35 ng m−2 h−1 at the Brazil site prior to burning. Gaseous mercury emissions averaged 74.9 ± 0.73 ng m−2 h−1 after burning of the cut forest in Brazil. Extrapolating our data, measured over several weeks to months, to a full year period, deforested soil is estimated to release an additional 2.30 g ha−1 yr−1 of gaseous mercury to the atmosphere in the Brazilian experiment and 0.41 g ha−1 yr−1 in the New York experiment. In Brazil, this represents an additional 50% of the mercury load released during the fire itself.Display Omitted
Keywords: Forest fire; Soil; Mercury; Amazon; Brazil; Land use change;

Characterization of atmospheric bioaerosols at 9 sites in Tijuana, Mexico by Lilia Hurtado; Guillermo Rodríguez; Jonathan López; J.E. Castillo; Luisa Molina; Miguel Zavala; Penelope J.E. Quintana (430-436).
The atmosphere is not considered a habitat for microorganisms, but can exist in the atmosphere as bioaerosols. These microorganisms in the atmosphere have great environmental importance through their influence on physical processes such as ice nucleation and cloud droplet formation. Pathogenic airborne microorganisms may also have public health consequences. In this paper we analyze the microbial concentration in the air at three sites in Tijuana, Mexico border during the Cal-Mex 2010 air quality campaign and from nine sites over the following year. Samples were collected by impaction with the air analyzer Millipore M Air T, followed by incubation and counting as colony forming units (CFU) of viable colonies. Airborne microbial contamination average levels ranged from a low of 230 ± 130 CFU/m³ in the coastal reference site to an average of 40,100 ± 21,689 CFU/m³ in the Tijuana river valley. We found the highest microbial load in the summer and the lowest values in the winter. Potentially pathogenic bacteria were isolated from the samples, with Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecalis being most common. This work is the first evaluation of bioaerosols in Tijuana, Mexico.
Keywords: Microorganisms airborne; Bioaerosols; Tijuana; Air quality;