Atmospheric Environment (v.72, #C)

Quantifying urban street configuration for improvements in air pollution models by Marloes Eeftens; Johan Beekhuizen; Rob Beelen; Meng Wang; Roel Vermeulen; Bert Brunekreef; Anke Huss; Gerard Hoek (1-9).
In many built-up urban areas, tall buildings along narrow streets obstruct the free flow of air, resulting in higher pollution levels. Input data to account for street configuration in models are difficult to obtain for large numbers of streets. We describe an approach to calculate indicators of this “urban canyon effect” using 3-dimensional building data and evaluated whether these indicators improved spatially resolved land use regression (LUR) models.Concentrations of NO2 and NO x were available from 132 sites in the Netherlands. We calculated four indicators for canyon effects at each site: (1) the maximum aspect ratio (building height/width of the street) between buildings on opposite sides of the street, (2) the mean building angle, which is the angle between the horizontal street level and the line of sight to the top of surrounding buildings, (3) median building angle and (4) “SkyView Factor” (SVF), a measure of the total fraction of visible sky. Basic LUR models were computed for both pollutants using common predictors such as household density, land-use and nearby traffic intensity. We added each of the four canyon indicators to the basic LUR models and evaluated whether they improved the model.The calculated aspect ratio agreed well (R 2 = 0.49) with aspect ratios calculated from field observations. Explained variance (R 2) of the basic LUR models without canyon indicators was 80% for NO2 and 76% for NO x , and increased to 82% and 78% respectively if SVF was included. Despite this small increase in R 2, contrasts in SVF (10th–90th percentile) resulted in substantial concentration differences of 5.56 μg m−3 in NO2 and 10.9 μg m−3 in NO x .We demonstrated a GIS based approach to quantify the obstruction of free air flow by buildings, applicable for large numbers of streets. Canyon indicators could be valuable to consider in air pollution models, especially in areas with low- and high-rise canyons.► Air pollution models struggle to accurately predict concentrations in street canyons. ► We developed an automated GIS-based method to derive quantitative canyon indicators. ► Our approach is based on 3-D building data, which are increasingly available. ► The derived indicators may be used in both land use regression and dispersion models. ► The canyon indicators helped explain pollution contrasts of NO2 in the Netherlands.
Keywords: Street configuration; Aspect ratio; Urban morphometry; Land use regression; Air pollution; Geographic information systems; Canyon; Nitrogen oxides;

Development of NO2 and NO x land use regression models for estimating air pollution exposure in 36 study areas in Europe – The ESCAPE project by Rob Beelen; Gerard Hoek; Danielle Vienneau; Marloes Eeftens; Konstantina Dimakopoulou; Xanthi Pedeli; Ming-Yi Tsai; Nino Künzli; Tamara Schikowski; Alessandro Marcon; Kirsten T. Eriksen; Ole Raaschou-Nielsen; Euripides Stephanou; Evridiki Patelarou; Timo Lanki; Tarja Yli-Tuomi; Christophe Declercq; Grégoire Falq; Morgane Stempfelet; Matthias Birk; Josef Cyrys; Stephanie von Klot; Gizella Nádor; Mihály János Varró; Audrius Dėdelė; Regina Gražulevičienė; Anna Mölter; Sarah Lindley; Christian Madsen; Giulia Cesaroni; Andrea Ranzi; Chiara Badaloni; Barbara Hoffmann; Michael Nonnemacher; Ursula Krämer; Thomas Kuhlbusch; Marta Cirach; Audrey de Nazelle; Mark Nieuwenhuijsen; Tom Bellander; Michal Korek; David Olsson; Magnus Strömgren; Evi Dons; Michael Jerrett; Paul Fischer; Meng Wang; Bert Brunekreef; Kees de Hoogh (10-23).
Estimating within-city variability in air pollution concentrations is important. Land use regression (LUR) models are able to explain such small-scale within-city variations. Transparency in LUR model development methods is important to facilitate comparison of methods between different studies. We therefore developed LUR models in a standardized way in 36 study areas in Europe for the ESCAPE (European Study of Cohorts for Air Pollution Effects) project.Nitrogen dioxide (NO2) and nitrogen oxides (NO x ) were measured with Ogawa passive samplers at 40 or 80 sites in each of the 36 study areas. The spatial variation in each area was explained by LUR modelling. Centrally and locally available Geographic Information System (GIS) variables were used as potential predictors. A leave-one out cross-validation procedure was used to evaluate the model performance.There was substantial contrast in annual average NO2 and NO x concentrations within the study areas. The model explained variances (R 2) of the LUR models ranged from 55% to 92% (median 82%) for NO2 and from 49% to 91% (median 78%) for NO x . For most areas the cross-validation R 2 was less than 10% lower than the model R 2. Small-scale traffic and population/household density were the most common predictors. The magnitude of the explained variance depended on the contrast in measured concentrations as well as availability of GIS predictors, especially traffic intensity data were important. In an additional evaluation, models in which local traffic intensity was not offered had 10% lower R 2 compared to models in the same areas in which these variables were offered.Within the ESCAPE project it was possible to develop LUR models that explained a large fraction of the spatial variance in measured annual average NO2 and NO x concentrations. These LUR models are being used to estimate outdoor concentrations at the home addresses of participants in over 30 cohort studies.► LUR models were developed in 36 study areas in Europe using a standardized approach. ► NO2 models explained a large fraction of concentration variability (median R 2 82%). ► Local traffic intensity data were important predictors for LUR model development.
Keywords: ESCAPE; Air pollution; NO2; NO x ; Land Use Regression (LUR) model;

Particulate emissions from different types of biomass burning by Yanyan Zhang; Daniel Obrist; Barbara Zielinska; Alan Gertler (27-35).
Biomass burning is a significant emission source of PM2.5(i.e., particulate matter with an aerodynamic diameter less than 2.5 μm), but few studies addressed the chemical composition of PM2.5 emissions from various types of fires. Here, we present results from a sampling campaign to quantify PM2.5 emissions from various types of prescribed burning activities using analysis of carbon (elemental carbon: EC; organic carbon: OC; and total carbon: TC); polar organic compounds (12 different compounds and four functional classes); water-soluble potassium (K+); and particle-bound mercury (PHg). Emissions were characterized for a series of prescribed burns in the Lake Tahoe basin in the western United States, along with controlled biomass combustion in a wood stove. In the field, emissions were collected from: (i) landscape underburns, consisting of wooden tissues, foliage, branches, and surface duff; (ii) pile burns, consisting mainly of wooden tissues stacked up to piles; (iii) mixed underburn/pile burns which consisted of a mix of the above; in a wood stove, burns included different fuel types collected from the Lake Tahoe basin, specifically (iv) wooden logs mainly of pine; (v) green foliage and branches from two dominant shrubs (manzanita and bitterbrush); and (vi) surface duff, mostly consisting of pine needle litter.Our data showed higher ratios of organic to elemental carbon in green fuels (19.2 ± 4.2) compared to dry, wooden logs (7.3 ± 1.9) both in prescribed burns in the field and in controlled stove combustion, indicating that more moisture in green biomass resulted in more smoldering-phase combustion. Further, OC/EC ratios were lower in wood stove burns compared to prescribed burns in the field, which we attribute to higher combustion temperatures in wood stove burns. The suite of 12 select polar organic compounds showed that the most prevalent compounds emitted across all burns were levoglucosan, mannosan, and resin acids (dehydroabietic, pimaric, and abietic acids), while emissions of inositols and arabitols were only significant in combustion of leaves from a broadleaf shrub indicating their potential use as tracers for green foliage. Water-soluble K+, a common tracer for biomass combustion, showed a clear difference between field understory burns (low K+) and wooden pile burns (nearly 5 times higher), suggesting that K+ can potentially be used for differentiating between different prescribed burning types. Finally, PHg emissions were lowest in green vegetation and underburns emissions, which was unexpected due to inherently higher Hg levels in green foliage and surface duff. Using multiple tracers (i.e., soluble potassium, carbon and mercury) allowed to separate emissions between prescribed burning, controlled stove burning, and ambient air which includes residential wood combustion.► Chemical speciation of PM2.5 emissions shows differences among different types of biomass burning. ► Emissions of polar organic compounds depend on fuel types during biomass burning. ► Combination of chemical tracers allows to characterize prescribed burning emissions.
Keywords: Biomass burning; Particulate emissions; Carbon emissions; Polar organic compounds; Soluble potassium; Mercury;

Spaceborne lidar and passive sensors with multi-wavelength, multi-angle and polarization capabilities onboard the A-Train provide unprecedented opportunities of observing above-cloud aerosols and direct radiative forcing. Significant progress has been made in recent years in exploring these new aerosol remote sensing capabilities and generating unique datasets. The emerging observations will advance the understanding of aerosol climate forcing.
Keywords: Aerosol above clouds; Radiative forcing; Satellite remote sensing;

A first-order, lumped capacitance model is used to describe the buffering of airborne chemical species by building materials and furnishings in the indoor environment. The model is applied to describe the interaction between formaldehyde in building materials and the concentration of the species in the indoor air. Storage buffering can decrease the effect of ventilation on the indoor concentration, compared to the inverse dependence of indoor concentration on the air exchange rate that is consistent with a constant emission rate source. If the exposure time of an occupant is long relative to the timescale of depletion of the compound from the storage medium, however, the total exposure will depend inversely on the air exchange rate. This lumped capacitance model is also applied to moisture buffering in the indoor environment, which occurs over much shorter depletion timescales of the order of days. This model provides a framework to interpret the impact of storage buffering on time-varying concentrations of chemical species and resulting occupant exposure. Pseudo-steady-state behavior is validated using field measurements. Model behavior over longer times is consistent with formaldehyde and moisture concentration measurements in previous studies.► A lumped parameter model is applied to describe emission and storage buffering of contaminants. ► Model is used to assess impact of ventilation on indoor formaldehyde exposure. ► Observations of depletion of stored contaminants can be described by model.
Keywords: Buffering capacity; Formaldehyde; Moisture;

Correlations between surface ozone and meteorological variables exhibit a north-south gradient over the Eastern United States (US), with the ozone–temperature correlation weakening and the ozone–humidity correlation transitioning from positive to negative south of 37°N. Using 17 years of hourly August ozone, nitrogen oxide, and isoprene measurements from the Environmental Protection Agency's Air Quality System and Photochemical Assessment Measurement Stations and hourly meteorological fields from the North American Land Data Assimilation System (Phase 2), we propose that the north-south transition and widely observed ozone–humidity correlation results from a shift in the soil moisture-atmosphere coupling regime. Due to soil water limitations over the Southeast, evapotranspiration and specific humidity increase following precipitation events, and this coincides with reductions in temperature and ozone precursors. Therefore, the negative ozone–humidity correlation in the Southeast is likely a manifestation of several meteorological factors directly influencing ozone production. Surface drying, as defined by the evaporative fraction, provides a better predictor of O3 than temperature, specific humidity, or radiation for the Southeast due to its ability to retain prior precipitation information and reflect same-day atmospheric conditions relevant to O3 production. Behavior of surface fluxes and coupling may be particularly relevant for prediction of seasonal and future O3 air quality, and further investigation into the links between land–atmosphere coupling and O3 is necessary.► We propose a physical mechanism producing the ozone-meteorology gradient. ► 17 years of hourly ozone and precursor observations and meteorological data are used. ► Ozone–humidity correlation is an artifact of land–atmosphere coupling regimes. ► Evaporative fraction is a better predictor of ozone for soil water-limited regimes.
Keywords: Ozone-meteorology correlations; Land–atmosphere coupling; Humidity; Evaporative fraction; Eastern United States; Surface ozone;

This paper presents a Bayesian hierarchical spatiotemporal method of interpolation, termed as Markov Cube Kriging (MCK). The classical Kriging methods become computationally prohibitive, especially for large datasets due to the O(n3) matrix decomposition. MCK offers novel and computationally efficient solutions to address spatiotemporal misalignment, mismatch in the spatiotemporal scales and missing values across space and time in large spatiotemporal datasets. MCK is flexible in that it allows for non-separable spatiotemporal structure and nonstationary covariance at the hierarchical spatiotemporal scales. Employing MCK we developed estimates of daily concentration of fine particulates matter ≤2.5 μm in aerodynamic diameter (PM2.5) at 2.5 km spatial grid for the Cleveland Metropolitan Statistical Area, 2000 to 2009. Our validation and cross-validation suggest that MCK achieved robust prediction of spatiotemporal random effects and underlying hierarchical and nonstationary spatiotemporal structure in air pollution data. MCK has important implications for environmental epidemiology and environmental sciences for exposure quantification and collocation of data from different sources, available at different spatiotemporal scales.► Novel method of interpolation across space and time. ► Computationally efficient method to estimate exposure at a given location and time. ► Hierarchical time-space Kriging.
Keywords: Time-space Kriging; Spatiotemporal hierarchical model; Gaussian Markov Random Fields; Nonstationarity; Bayesian computation; Fine particulate matter PM2.5;

Measurements of N2O emissions from different vegetable fields on the North China Plain by Tiantian Diao; Liyong Xie; Liping Guo; Hongliang Yan; Miao Lin; He Zhang; Jia Lin; Erda Lin (70-76).
Few studies have measured the N2O emission fluxes from vegetable fields. In order to identify the characteristics and the influencing factors of N2O emissions from different vegetable fields, we measured N2O emissions for a full year from four typical fields, including an open-ground vegetable field that has produced vegetables for over 20 years (OV20), a recently developed open-ground vegetable field that was converted from a maize field three years earlier (OV3), a recently developed greenhouse vegetable field that was converted from a maize field 3 years earlier (GV3) and a typical local maize field (Maize). Four different fertilization treatments were set additionally in the recently developed open-ground vegetable field. These were: no fertilizer or manure (OV3_CK), manure only (OV3_M) and the combination of manure with different rates of chemical fertilizer application (OV3_MF1 and OV3_MF3). The results showed that N2O emission fluxes fluctuated between 0.3 ± 0.1 and 912.4 ± 80.0 mg N2O–N m−2 h−1 with the highest emission peak occurring after fertilization followed by irrigation. Nitrogen application explained 64.6–84.5% of the N2O emission in the vegetable fields. The magnitude of the emission peaks depended on the nitrogen application rate and the duration of the emission peaks was mainly associated with soil temperature when appropriate irrigation was given after fertilization. The N2O emission peaks occurred later and lasted for a longer period when the soil temperature was <24 °C in May. However, emission peaks occurred earlier and lasted for a shorter period when the soil temperature was around 25–33 °C from June to August. The annual N2O emissions from the fertilized vegetable fields were 1.68–2.38 times higher than that from the maize field, which had an emission value of 2.88 ± 0.10 kg N ha−1 a−1. The N2O emission factor (EF) of manure nitrogen was 0.07% over the whole year, but was 0.11% and 0.02% in the spring cucumber season and the autumn cabbage season, respectively. The EF of chemical nitrogen was 1.10–1.78% for the vegetable field over the whole year and it was higher in recently developed vegetable field than in the established field (1.54–1.78% vs. 1.10%). Vegetable fields may contribute greatly to the national greenhouse gas inventories due to the high fertilizer application rates, frequent irrigation and an increased number of tillage–planting cycles.► N2O emitted from vegetable fields and the typical cereal fields are compared. ► Characteristics of N2O emissions from vegetable soils are studied. ► Manure nitrogen shows lower emission factor than chemical nitrogen. ► Importance of N2O from vegetable fields to the national N2O inventories is discussed.
Keywords: Greenhouse gas; N2O; Vegetable soil; Emission factor; Greenhouse gas inventory;

A quantitative liquid chromatography–mass spectrometry (LC–MS) technique was developed to measure the concentrations of heterocyclic nitrogen compounds in ambient fine aerosols (PM2.5). Quadrupole time-of-flight (Q-TOF) MS technology was used to provide both accurate-mass and MS/MS data for confirmation of chemical formula and nitrogen compound structure. The fine aerosol was collected over the winter and summer seasons at an experimental monitoring station at Duke Forest in North Carolina U.S.A. 3-Hydroxypyridine and two β-carbolines, harmane, and norharmane, were observed in both campaigns at concentrations lower in summer (sum = 332 pg m−3; N = 27) than winter (554 pg m−3; N = 31). Aminopyridines, dimethylpyrazoles, and hydroxymethyl-pyridines were observed in the winter aerosols with a total estimated average concentration of 779 pg m−3. These results demonstrate the possibility of enhanced speciation and provide a first glance at heterocyclic amines in the water-soluble organic nitrogen (ON) fraction of fine aerosols collected from a forest atmosphere.
Keywords: Nitrogen heterocyclics; Heterocyclic amines; Organic nitrogen; Water-soluble organic compounds; Biomass burning; β-Carbolines; Duke Forest;

Evidence of biomass burning aerosols in the Barcelona urban environment during winter time by M. Viana; C. Reche; F. Amato; A. Alastuey; X. Querol; T. Moreno; F. Lucarelli; S. Nava; G. Calzolai; M. Chiari; M. Rico (81-88).
The influence of biomass burning (BB) aerosols, whether of regional or local origin, on fine aerosol levels in the Barcelona urban environment (Spain) was investigated. High-time resolved data on light-absorbing aerosols and inorganic tracers in PM2.5 were combined to this end during a dedicated sampling campaign carried out in winter 2011. The evaluation of PM inorganic components and equivalent black carbon evidenced that local-scale BB emissions were not detectable, whereas a source of K, different to vehicular traffic (road dust) and construction/demolition dust re-suspension, was detectable in the urban area. Source apportionment analysis evidenced the contribution from one source traced by S (62% of the source profile) and K (16% of the source profile), which was interpreted as regional-scale transport of secondary aerosols including BB contributions. The S/K ratio for this source (S/K = 4.4) indicated transport of the polluted air masses, as occurs from the rural areas towards the Barcelona urban environment. On average for the study period, the contribution of K-related aerosols from regional BB to PM2.5 levels in the urban environment was estimated as 1.7 μg/m3 as a daily mean, accounting for 8% of the PM2.5 mass during the winter period under study. The contribution from this source to urban aerosols should be lower on the annual scale.► Biomass burning emissions were detected in a typical Mediterranean urban area. ► This was achieved with high-time resolved inorganic tracers and BC. ► No organic tracers (e.g., anhydrosugars) were used. ► Biomass emissions in the urban area had a regional-scale origin. ► Biomass burning contributions accounted for 8% PM2.5.
Keywords: Secondary organic aerosol; Source apportionment; PMF; Agricultural; Regional-scale transport; Aged aerosols;

Monte Carlo sampling of pre-specified parameter ranges has been used to replace single ‘best estimate’ Photochemical Trajectory Model runs with 9006 ‘acceptable’ model runs that were each consistent with the observations of elevated O3 during July 2006 at a rural location in southern England. These acceptable parameter sets were then used for probabilistic evaluation of policy relevant photochemical oxidant control strategies, based on 30% reductions in VOC and NO x precursor emissions and the geographic locations where the emission reductions were carried out. Indicator species ratios were used to complete a diagnostic evaluation of model performance. The chemical mechanism employed in the base case model was replaced with four other mechanisms from the literature. Probabilistic uncertainty analysis showed that the results of the policy-relevant scenarios showed little or no sensitivity to chemical mechanism choice. A large degree of error compensation could be achieved through the selection of acceptable parameter sets and this hid the differences between the five chemical mechanisms studied.► Monte Carlo techniques can quantify uncertainties in ozone predictions. ► VOC- versus NO x -sensitivity changes from day-to-day. ► Impacts of policy-relevant scenarios are independent of chemical mechanisms.
Keywords: Monte Carlo uncertainty analysis; Ozone; NO x and VOC emissions;

A series of simulation chamber experiments has been performed on the atmospheric oxidation of acenaphthene at (293 ± 3) K in 1 atm of purified air. Rate coefficients for reaction with hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone have been determined using the relative rate technique. The values obtained for reaction with OH and O3 were (in units of cm3 molecule−1 s−1) (9.89 ± 0.51) × 10−11 and (1.79 ± 0.10) × 10−19 respectively. The rate coefficient for reaction with NO3 was found to be dependent on NO2 concentration and is given by (4.16 ± 0.70) × 10−13 + (3.45 ± 1.73) × 10−27[NO2] cm3 molecule−1 s−1. A denuder-filter sampling system coupled with off-line GC–MS analysis was used to collect and identify gas- and particle-phase products of the OH and NO3 initiated oxidation of acenaphthene. For the OH reaction, a range of ring-retaining and ring-opening products were identified in both phases, although some species, including nitroacenaphthene and 1,8-naphthalic anhydride, were found exclusively in the particle phase. In particular, the identification of 1-acenaphthenone and naphthalene-1,8-dicarbaldehyde amongst the products indicates that H-atom abstraction from the cyclopenta-fused ring is an important reaction pathway, along with OH addition to the aromatic ring. For the NO3 reaction, 1-acenaphthenone and nitroacenaphthene were identified as the major gas- and particle-phase products respectively. Possible reaction mechanisms for the formation of these products are proposed.► Gas-phase reactions with OH and NO3 radicals are important degradation processes. ► Atmospheric oxidation yields a range of ring-retaining and ring-opening products. ► H-atom abstraction and OH addition are important reaction pathways in OH reactions. ► Acenaphthene oxidation products are detected in both gas and particle phases.
Keywords: Gas-phase; Acenaphthene; Kinetic; Mechanism; Atmospheric chemistry;

NO3 radical, OH radical and O3-initiated secondary aerosol formation from aliphatic amines by Xiaochen Tang; Derek Price; Eric Praske; Su Anne Lee; Morgan A. Shattuck; Kathleen Purvis-Roberts; Philip J. Silva; Akua Asa-Awuku; David R. Cocker (105-112).
Aliphatic amines enter the atmosphere from a variety of sources, and exist in both gas and particle phases in the atmosphere. Similar to ammonia, amines can form inorganic salts through acid–base reactions. However, the atmospheric behavior of amines with atmospheric oxidants (e.g. the nitrate radical (NO3), the hydroxyl radical (OH), O3) is still poorly understood. In this study, chamber experiments were conducted to explore the reaction between three aliphatic amines and HNO3/O3/NO3/OH. Effects of water vapor were also explored by conducting experiments under different relative humidity conditions (RH<0.1% to ∼40%). Results show that all three amines have a high potential to form secondary aerosol in reactions with NO3, and are affected by the presence of water vapor. DEA and BA are capable of forming a significant amount of stable inorganic salt at ppb level concentrations, while TMA tends to form mostly non-salt secondary organic aerosol under dry conditions. The OH photooxidation of amines has much lower secondary aerosol yield and is independent of relative humidity, while ozonolysis produced negligible amount of aerosol. Secondary aerosol from OH oxidation was composed of organic components only, due to the lack of acid source. This study shows that night time chemistry of aliphatic amines can produce secondary organic and inorganic aerosol mixtures, and the relative contribution of each component depends on the environment relative humidity.► We study the forming potential and composition of secondary aerosol from three aliphatic amines in the environmental chamber. ► OH photooxidation and ozonolysis of the three amines lead to less amount of aerosol than reactions with nitrate radicals. ► Negligible effect of water vapor has been observed on the aerosol yield of amine OH photooxidation. ► Presence of water vapor impacts on salt formation in the nitrate radical–amine reactions. ► Acid-base reaction is a major pathway in reactions between nitrate radical and butylamine/diethylamine.
Keywords: Secondary aerosol; Amine; Salt formation; Relative humidity;

Vehicle derived pollutants as well as industrial emissions simultaneously release deleterious fine-grained particulates and magnetic particles into the atmosphere These magnetic particles are derived from the presence of iron (as impurities in fuels, industrial emissions, street dust, rock dust etc.), often a mix of strongly magnetic (magnetite-like) and weakly magnetic (haematite-like) iron oxides. Present review discusses the problem of particulate matter (PM) pollution, its environmental geomagnetic studies with special reference to biomagnetic monitoring through roadside plant leaves. Biomagnetic monitoring with the roadside plant leaves, is very recent thrust area in the field of PM pollution science. An overview of the researches on implications of environmental geo-magnetic studies is presented in this paper for sediments, street dust and vegetation. The concept of environmental magnetism as a proxy for atmospheric pollution levels has been reported by several researchers based on analysis of soils and street or roof dust; however, very few researches have emphasized the use of roadside plant leaves in monitoring the dust. Magnetic biomonitoring of pollutants by measurements taken from roadside tree leaves is potentially efficient and cost-effective. Finally, several case studies on biomagnetic monitoring in Indian subcontinent by our group have been mentioned in detail. Nevertheless, there is still paucity of focused research works in the multifaceted environmental dimensions of magnetic monitoring particularly biomagnetic monitoring of particulate pollution with roadside plant leaves which possess the potential to become a new frontier in the field of atmospheric science and technology.► An overview on the global problem of particulate matter (PM) pollution. ► Implications of environmental magnetism in PM study. ► Critical review on bio-magnetic monitoring of the PM through roadside plant leaves. ► Case studies on bio-magnetic monitoring.
Keywords: Biomagnetic monitoring; Climate change; Dust; Mining; Environmental geomagnetism;

Monoterpene emissions from bark beetle infested Engelmann spruce trees by Hardik S. Amin; Rachel S. Russo; Barkley Sive; E. Richard Hoebeke; Craig Dodson; Ian B. McCubbin; A. Gannet Hallar; Kara E. Huff Hartz (130-133).
Bark beetle infestation impacts the health of coniferous forests, which are an important source of volatile organic compounds (VOCs) to the atmosphere. The types and amounts of VOCs emitted from forests can influence secondary organic aerosol (SOA) formation and impact overall air quality. In this initial work, the impact of bark beetle infestation on SOA precursors from Engelmann spruce is assessed. The VOCs emitted from the trunk of infested and healthy spruce trees were sampled using both sorbent traps and evacuated canisters that were analyzed by gas chromatography/mass spectroscopy. The samples from the infested spruce tree suggest a nine-fold enhancement in the total VOC emissions. The dominant VOCs in the infested spruce trees were 3-carene, β-pinene, and α-pinene. The increase observed in VOCs sampled at the trunk of the infested spruce was consistent with increases observed at infested lodgepole pine trunks. However, the types and amounts of VOCs emitted from Engelmann spruce and lodgepole pine are different, which suggests that additional measures of VOC emissions are needed to characterize the impact of bark beetle infestation on VOC emissions and SOA precursors.
Keywords: Biogenic volatile organic compound emissions; Bark beetle; Secondary organic aerosol; Engelmann spruce;

Evaluation of the CALIOPE air quality forecasting system for epidemiological research: The example of NO2 in the province of Girona (Spain) by Inmaculada Aguilera; Xavier Basagaña; María Teresa Pay; David Agis; Laura Bouso; Maria Foraster; Marcela Rivera; José María Baldasano; Nino Künzli (134-141).
Air quality models are being increasingly used to estimate long-term individual exposures to air pollution in epidemiological studies. Most of them have been evaluated against measurements from a limited number of monitoring stations, which may not properly reflect the exposure characteristics of the study population.We evaluated the performance of the high-resolution CALIOPE air quality forecasting system over a large sample of passive measurements of NO2 conducted at 635 home outdoor locations of the Girona province (Spain) during several 4-week sampling campaigns over one year (July 2007–June 2008). Sampling sites were superposed over the 4 km × 4 km CALIOPE grid, and average NO2 modeled concentrations were derived for all measurements conducted during the same sampling campaign at all the sampling sites located within the same grid cell. In addition, the ratio between measured and modeled concentrations for the whole study period at one fixed monitoring station was used to post-process the modeled values at the home outdoor locations.The correlation between measured and modeled concentrations for the entire study area (which includes urban settings, middle-size towns, and rural areas) was 0.78. Modeled concentrations were underestimated in the whole study area. After correcting the modeled concentrations by the measured to modeled ratio at the fixed station (r = 0.25), they were very similar to the measured concentrations (27.7 μg m−3 and 29.3 μg m−3, respectively). However, the performance of the modeling system depends on the type of subarea and is affected by the sub-grid emission sources.The evaluation over the heterogenous Girona province showed that CALIOPE is able to reproduce the spatial variability of 4-week NO2 concentrations at the small regional level. CALIOPE output data is a valuable tool to complement study-specific air pollution measurements by incorporating regional spatial variability as well as short- and long-term temporal variability of background pollution in epidemiological research.► We evaluated the performance of an air quality model against NO2 measurements. ► The model reflected the spatial variability of NO2 at the small regional level. ► The model performance depended on the type of area. ► The model provided short- and long-term temporal variability of background pollution. ► Model output data show great potential for being used in epidemiological studies.
Keywords: Air quality modeling; Model evaluation; NO2; Passive sampling;

When using the mean wind direction in Reynolds-averaged Navier–Stokes (RANS) simulations of atmospheric dispersion, it is well documented that peak concentration levels are often overestimated, and lateral spreading underestimated. A number of studies report that if the variability of wind directions observed in experiments is included in the boundary conditions, peak levels improve, but lateral spreading is overestimated. In the current work, we argue that fluctuations in wind directions observed in experiments are partly accounted for by the modeled turbulence in RANS simulations; and hence, the effective variability that should be used as a boundary condition to the simulations, needs to be lower than experimentally measured. A simple approach is proposed that reduces the variability based on turbulence levels predicted in the RANS turbulence model. We test the approach by performing a series of dispersion simulations of the well-documented Prairie Grass experiments, and demonstrate that simulations improve significantly.► Effect of wind variability at the inlet of RANS dispersion simulations is studied. ► Variability observed in experiments is already partly included in the RANS model. ► A method is proposed to estimate a reduced level of variability required for RANS. ► We validate the approach with simulations of the Prairie-Grass Experiment. ► Results improve significantly compared to RANS with no or full wind variability.
Keywords: Dispersion; Atmospheric boundary layer; Wind fluctuations; Project Prairie Grass;

Hydrogen isotope analysis of benzene and toluene emitted from vehicles by Nami Kikuchi; Hiroto Kawashima (151-158).
The isotopic analysis of atmospheric volatile organic compounds (VOCs), and in particular their hydrogen isotope ratio (δ2H), has the potential to be an effective tool for clearly identifying sources of VOCs. However, to date there have been very few such analyzes. Here, we have analyzed the δ2H values of VOCs using thermal desorption and chromatography, thermal conversion, and isotope ratio mass spectrometry (TD-GC/TC/IRMS). After determining the analytical conditions needed for high precision and accurate analysis, we adopted minimum peak area thresholds of 10 Vs for the low concentration samples and 15 Vs for other samples. We also confirmed that breakthrough during adsorption of samples would have only minimal effect. We found that the collected samples could be stored for at least 7 days. Precisions of 1.1‰–5.3‰ (n = 7) were obtained for 28 standard compounds in a standard gas containing 58 VOCs (C6–C11). Next, we collected the exhaust gas produced in cold mode and hot mode from five vehicles, and measured the δ2H values. For benzene, we found that the δ2H value for the hot mode vehicle emissions was 19.3–104.7‰ lighter than that for the cold mode, while the δ2H value of the vaporized gasoline was 0.7–25.2‰ close to that in the cold mode. It should, therefore, be possible to distinguish cold mode vehicle emissions from those of the hot mode by analyzing the hydrogen isotope ratio. For benzene, particularly, the difference in δ2H values between 2 modes is important since emitted in large quantity from vehicles generally. Additionally, we measured VOCs in vaporized gasoline and roadside air, and compared the results with those for vehicle emissions. The roadside samples were characterized mainly by the hot mode. It has been shown that the hot mode has a significant impact on roadside VOCs, if no isotopic fractionation in the atmosphere is assumed. The results suggest that our approach could improve our understanding of the origin and fate of atmospheric VOCs, by allowing measurement of the δ2H values of further target compounds and sources.► We investigated vehicle sources to use δ2H of benzene and toluene. ► We found that the δ2H values for the hot mode vehicle emissions and the cold mode were different. ► The results suggest that our approach could improve our understanding of the origin and fate of atmospheric VOCs.
Keywords: Volatile organic compounds; Stable hydrogen isotope ratio; Vehicle emission; Source apportionment; Thermal desorption; TD-GC/TC/IRMS;

A statistical analysis is made of vertical changes in CO2 mole fraction and its seasonal variations in the free troposphere from the data of flask aircraft measurements over Briggsdale and Carr, Colorado, USA (∼40° N, ∼104° W) during years 1992–2011. Polynomials give good approximations for the general CO2 19-year grows rates at different altitudes in the troposphere. The averaged over altitudes 4–8 km 19-year mean CO2 mole fraction related to year 2002 is 372.1 ± 0.1 ppm, its mean growth rate is 1.97 ± 0.02 ppm yr−1 and acceleration of the grows is 0.019 ± 0.01 ppm yr−2. Observed CO2 seasonal cycles, also amplitudes and phases of their spectral components are less variable in the troposphere above altitude 4–5 km than below. This may reflect better mixing and larger influence of atmospheric circulation there, than at lower altitudes. Annual and semiannual components could prevail in average CO2 seasonal cycle in the troposphere above altitude 4–5 km, while shorter period components are more important at lower altitudes. The amplitude of the semiannual component grows in time faster than the amplitude of annual component. In the lower part of the troposphere, transitions from low-altitude CO2 characteristics (partly influenced by local sources) to more homogeneous ones in the upper troposphere are observed.
Keywords: Carbon dioxide; CO2; Atmosphere; Aircraft; Flask measurements; Seasonal variation; Climatology;

Heterogeneous photochemical reaction of ozone with anthracene adsorbed on mineral dust by Jinzhu Ma; Yongchun Liu; Qingxin Ma; Chang Liu; Hong He (165-170).
The heterogeneous reactions of O3 with anthracene adsorbed on TiO2 and on Asian dust storm particles were investigated in the dark and in the presence of light. The reaction rate constants of the heterogeneous reaction between O3 and anthracene adsorbed on TiO2 were increased by a factor of 1.5 in the presence of light compared to the dark conditions. Anthraquinone, which was identified as the main surface product of anthracene reacted with O3 in the dark, can react with O3 quickly in the presence of light. The reactions on Asian dust storm particles exhibited pseudo-first-order kinetics for anthracene loss, and the reactions between O3 and anthracene adsorbed on Asian dust storm particles proceed by the Langmuir–Hinshelwood mechanism in the dark and in the presence of light. At extremely high ozone concentrations, the degradation of anthracene is enhanced by a factor of 3 in the presence of light compared to the dark conditions.► Reactions of O3 with anthracene on TiO2 and Asian dust were photo-enhanced. ► Anthraquinone can react with O3 quickly in the presence of light. ► Reactions of O3 with anthracene adsorbed on Asian dust proceed by the L–H mechanism.
Keywords: Anthracene; TiO2; Asian dust storm particles; Ozone; Heterogeneous photochemical reactions; Kinetics;

Formaldehyde and acetaldehyde emissions from residential wood combustion in Portugal by Mário Cerqueira; Luís Gomes; Luís Tarelho; Casimiro Pio (171-176).
A series of experiments were conducted to characterize formaldehyde and acetaldehyde emissions from residential combustion of common wood species growing in Portugal. Five types of wood were investigated: maritime pine (Pinus pinaster), eucalyptus (Eucalyptus globulus), cork oak (Quercus suber), holm oak (Quercus rotundifolia) and pyrenean oak (Quercus pyrenaica). Laboratory experiments were performed with a typical wood stove used for domestic heating in Portugal and operating under realistic home conditions. Aldehydes were sampled from diluted combustion flue gas using silica cartridges coated with 2,4-dinitrophenylhydrazine and analyzed by high performance liquid chromatography with diode array detection. The average formaldehyde to acetaldehyde concentration ratio (molar basis) in the stove flue gas was in the range of 2.1–2.9. Among the tested wood types, pyrenean oak produced the highest emissions for both formaldehyde and acetaldehyde: 1772 ± 649 and 1110 ± 454 mg kg−1 biomass burned (dry basis), respectively. By contrast, maritime pine produced the lowest emissions: 653 ± 151 and 371 ± 162 mg kg−1 biomass (dry basis) burned, respectively. Aldehydes were sampled separately during distinct periods of the holm oak wood combustion cycles. Significant variations in the flue gas concentrations were found, with higher values measured during the devolatilization stage than in the flaming and smoldering stages.► Aldehyde emissions from residential wood combustion were examined. ► Formaldehyde emissions were dominant over acetaldehyde emissions. ► The highest emission factors were found with pyrenean oak combustion tests. ► The database of emission factors for residential wood combustion in Europe was extended.
Keywords: Formaldehyde; Acetaldehyde; Wood stove; Biomass combustion; Emissions;

Modeling aerosol impacts on atmospheric visibility in Beijing with RAMS-CMAQ by Xiao Han; Meigen Zhang; Jinhua Tao; Lili Wang; Jian Gao; Shulan Wang; Fahe Chai (177-191).
A typical heavy air pollution episode occurred over the North China Plain (NCP) in December 2010. The air quality in Beijing and its surrounding regions worsened during the period December 17 to 22, and local visibility became significantly affected by the high pollution levels. The air quality modeling system RAMS-CMAQ coupled with an aerosol optical property scheme was applied to simulate the trace gases and major aerosol components in the NCP to obtain an in-depth understanding of the relationship between regional low visibility and aerosol particles. The model performance was evaluated using various observation data, such as meteorological factors (temperature, relative humidity, and wind field), gaseous pollutants (SO2, NO2, and O3), PM2.5, PM10, and visibility at several measurement stations. The modeled meteorological field and visibility were in good agreement with observations from December 2010. The modeled mass concentrations of gaseous pollutants and aerosol particles also suitably captured the magnitude and variation features of the observation data, especially during the air pollution episode. The simulated results showed that during this pollution episode, low visibility (lower than 10 km) occurred mainly in Beijing, Tianjin, Hebei, and Shandong. The analysis and sensitivity test indicated that the aerosol particles larger than PM2.5 and the water uptake effect of aerosol optical properties could not significantly influence visibility. Thus, the low visibility was primarily caused by the high mass burden of PM2.5as a result of the local pollutant accumulation and long-range transport. Statistics showed that the visibility variation was closely inversely related to the variation in PM2.5 in most regions in the NCP. Visibility decreased lower than 10 km when the mass concentration of PM2.5 exceeded 75 μg m−3 to 85 μg m−3 in the NCP. Sulfate and nitrate were the two major inorganic aerosol components of PM2.5 that evidently decreased visibility by contributing 40% to 45% to the total extinction coefficient value.► A heavy pollution episode occurred in North China Plain is identified and simulated by RAMS-CMAQ. ► The pollution processes and the relationship between visibility and aerosol are discussed. ► Model simulations indicate the low atmospheric visibility was caused by high PM2.5 concentration.
Keywords: Visibility; Aerosol; CMAQ; Haze; North China Plain;

In addition to industrial facilities, fuel combustion, forest fires and dust erosion, exhaust and non-exhaust vehicle emissions are an important source of ambient air respirable particulate matter (PM10). Non-exhaust vehicle emissions are formed from wear particles of vehicle components such as brakes, clutches, chassis and tires. Although the non-exhaust particles are relatively minor contributors to the overall ambient air particulate load, reliable exposure estimates are few. In this study, a global sampling program was conducted to quantify tire and road wear particles (TRWP) in the ambient air in order to understand potential human exposures and the overall contribution of these particles to the PM10. The sampling was conducted in Europe, the United States and Japan and the sampling locations were selected to represent a variety of settings including both rural and urban core; and within each residential, commercial and recreational receptors. The air samples were analyzed using validated chemical markers for rubber polymer based on a pyrolysis technique. Results indicated that TRWP concentrations in the PM10 fraction were low with averages ranging from 0.05 to 0.70 μg m−3, representing an average PM10 contribution of 0.84%. The TRWP concentration in air was associated with traffic load and population density, but the trend was not statistically significant. Further, significant differences across days were not observed. This study provides a robust dataset to understand potential human exposures to airborne TRWP.► Tire and road wear particles (TRWP) are part of non-exhaust emissions from vehicles. ► We conducted air sampling on 3 continents to determine the potential for exposure to TRWP. ► Chemical markers specific to tire tread were used to quantify TRWP in PM10. ► Average air concentrations ranged from 0.05 to 0.70 μg m−3. ► TRWP contributed on average 0.84% to total PM10.
Keywords: Tire; Particles; PM10;