Atmospheric Environment (v.44, #8)

Identification and quantification of methyl halide sources in a lowland tropical rainforest by Emanuel Blei; Catherine J. Hardacre; Graham P. Mills; Kate V. Heal; Mathew R. Heal (1005-1010).
In conjunction with the OP3 campaign in Danum Valley, Malaysian Borneo, flux measurements of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were performed from both tropical plant branches and leaf litter in June and July 2008. Live plants were mainly from the Dipterocarpaceae family whilst leaf litter samples were representative mixtures of different plant species. Environmental parameters, including photosynthetically-active radiation, total solar radiation and air temperature, were also recorded. The dominant factor determining magnitude of methyl halide fluxes from living plants was plant species, with specimens of the genus Shorea showing persistent high emissions of both gases, e.g. Shorea pilosa: 65 ± 17 ng CH3Cl h−1 g−1 (dry weight foliage) and 2.7 ± 0.6 ng CH3Br h−1 g−1 (dry weight foliage). Mean CH3Cl and CH3Br emissions across 18 species of plant were 19 (range, <LOD −76) and 0.4 (<LOD −2.9) ng h−1 g−1 respectively; fluxes from leaf litter were 1–2 orders of magnitude smaller per dry mass. CH3Cl and CH3Br fluxes were weakly correlated. Overall, the findings suggest that tropical rainforests make an important contribution to global terrestrial emissions of CH3Cl, but less so for CH3Br.
Keywords: CH3Br; CH3Cl; Dipterocarp; Emission; Rainforest; South-east Asia; Stratospheric ozone;

Observation of SO2 dry deposition velocity at a high elevation flux tower over an evergreen broadleaf forest in Central Taiwan by Jeng-Lin Tsai; Chien-Lung Chen; Ben-Jei Tsuang; Pei-Hsuan Kuo; Kuo-Hsin Tseng; Ting-Fang Hsu; Bor-Hung Sheu; Chiung-Pin Liu; Ming-Tung Hsueh (1011-1019).
A 60-m flux tower was built on a 2100 m mountain for the measurement of the air pollutant concentration and the evaluation of dry deposition velocity in Central Taiwan. The tower was constructed in an evergreen broadleaf forest, which is the dominant species of forest in the world. Multiple-level SO2 concentrations and meteorological variables at the site were measured from February to April 2008. The results showed that the mean dry deposition velocities of SO2 were 0.61 cm s−1 during daytime and 0.27 cm s−1 during nighttime. From the comparison of the monthly data, a tendency was observed that the dry deposition velocity increases with LAI and solar radiation. Furthermore, it was observed that the deposition velocity was larger over wet canopy than over dry canopy, and that higher deposition velocities in the wet season were mainly caused by non-stomatal uptake of wet canopy. Over wet canopy, the mean dry deposition velocities of SO2 were estimated to be 0.83 cm s−1 during daytime and 0.47 cm s−1 during nighttime; and 0.44 cm s−1 during daytime and 0.19 cm s−1 during nighttime over dry canopy. There is good agreement between the results of this study and those in other studies and the predictions of . The medians (geometric means) of derived r c during daytime are 233 (266) m s−1 over dry canopy and 147 (146) m s−1 over wet canopy. It was found that solar radiation is the critical important meteorological variable determining stomatal resistance during daytime. For non-stomatal resistance, clear dependencies were observed on the friction velocity and relative humidity.
Keywords: East Asia; Sulfur dioxide; Dry deposition; Stomatal and non-stomatal resistances; Evergreen broadleaf forest;

High ozone levels in the northeast of Portugal: Analysis and characterization by A. Carvalho; A. Monteiro; I. Ribeiro; O. Tchepel; A.I. Miranda; C. Borrego; S. Saavedra; J.A. Souto; J.J. Casares (1020-1031).
Each summer period extremely high ozone levels are registered at the rural background station of Lamas d'Olo, located in the Northeast of Portugal. In average, 30% of the total alert threshold registered in Portugal is detected at this site. The main purpose of this study is to characterize the atmospheric conditions that lead to the ozone-rich episodes at this site. Synoptic patterns anomalies and back trajectories cluster analysis were performed, for the period between 2004 and 2007, considering 76 days when ozone maximum hourly concentrations were above 200 μg m−3. The obtained atmospheric anomaly fields suggested that a positive temperature anomaly is visible above the Iberian Peninsula. A strong wind flow pattern from NE is observable in the North of Portugal and Galicia, in Spain. These two features may lead to an enhancement of the photochemical production and to the transport of pollutants from Spain to Portugal. In addition, the 3D mean back trajectories associated to the ozone episode days were analysed. A clustering method has been applied to the obtained back trajectories. Four main clusters of ozone-rich episodes were identified, with different frequencies of occurrence: north-westerly flows (11%); north-easterly flows (45%), southern flow (4%) and westerly flows (40%). Both analyses highlight the NE flow as a dominant pattern over the North of Portugal during summer. The analysis of the ozone concentrations for each selected cluster indicates that this northeast circulation pattern, together with the southern flow, are responsible for the highest ozone peak episodes. This also suggests that long-range transport of atmospheric pollutants is the main contributor to the ozone levels registered at Lamas d'Olo. This is also highlighted by the correlation of the ozone time-series with the meteorological parameters analysed in the frequency domain.
Keywords: High-ozone episodes; Long-range transport; Synoptic patterns anomalies; Back trajectories analysis; Spectral analysis;

High-resolution mass spectrometry analysis of secondary organic aerosol generated by ozonolysis of isoprene by Tran B. Nguyen; Adam P. Bateman; David L. Bones; Sergey A. Nizkorodov; Julia Laskin; Alexander Laskin (1032-1042).
The chemical composition of secondary organic aerosol (SOA) generated from the ozonolysis of isoprene (C5H8) in the presence of an OH scavenger was examined using high-resolution electrospray ionization mass spectrometry (ESI-MS) in the mass range m/z = 50–1000. The chemical composition of SOA is complex, with more than 1000 assigned peaks observed in the positive and negative ion mode spectra. Only a small fraction of peaks correspond to known products of isoprene oxidation, such as pyruvic acid, glycolic acid, methylglyoxal, etc. The absolute majority of the detected peaks correspond to highly oxidized oligomeric constituents of SOA, with an average O:C molar ratio of 0.6. The corresponding organic mass (OM) to organic oxygen (OO) ratio is 2.4. Approximately 8% of oxygen atoms in SOA are in the form of peroxides, as quantified with an iodide test. Double bond equivalency (DBE) factors, representing the sum of all double bonds and rings, increase by 1 for every 1–2 additional carbon atoms in the molecule. The number of unoxidized C=C double bonds is estimated to be less than 10%; the remaining DBE is due to C=O carbonyl groups. Kendrick analysis suggests that the prevalent oligomer building blocks are small carbonyls with a C1–C2 skeleton. Formaldehyde (CH2O) is identified as the most common repetitive building block in the observed oligomeric compounds.
Keywords: Biogenic aerosol; SOA; Gas-particle partitioning; Peroxides; Carbonyls; Organic carbon; Oligomers;

Dust emissions created by low-level rotary-winged aircraft flight over desert surfaces by J.A. Gillies; V. Etyemezian; H. Kuhns; J.D. McAlpine; J. King; S. Uppapalli; G. Nikolich; J. Engelbrecht (1043-1053).
There is a dearth of information on dust emissions from sources that are unique to U.S. Department of Defense testing and training activities. Dust emissions of PM10 and PM2.5 from low-level rotary-winged aircraft travelling (rotor-blade ≈7 m above ground level) over two types of desert surfaces (i.e., relatively undisturbed desert pavement and disturbed desert soil surface) were characterized at the Yuma Proving Ground (Yuma, AZ) in May 2007. Fugitive emissions are created by the shear stress of the outflow of high speed air created by the rotor-blade. The strength of the emissions was observed to scale primarily as a function of forward travel speed of the aircraft. Speed affects dust emissions in two ways: 1) as speed increases, peak shear stress at the soil surface was observed to decline proportionally, and 2) as the helicopter's forward speed increases its residence time over any location on the surface diminishes, so the time the downward rotor-generated flow is acting upon that surface must also decrease. The state of the surface over which the travel occurs also affects the scale of the emissions. The disturbed desert test surface produced approximately an order of magnitude greater emission than the undisturbed surface. Based on the measured emission rates for the test aircraft and the established scaling relationships, a rotary-winged aircraft similar to the test aircraft traveling 30 km h−1 over the disturbed surface would need to travel 4 km to produce emissions equivalent to one kilometer of travel by a light wheeled military vehicle also traveling at 30 km h−1 on an unpaved road. As rotary-winged aircraft activity is substantially less than that of off-road vehicle military testing and training activities it is likely that this source is small compared to emissions created by ground-based vehicle movements.
Keywords: Rotary-winged aircraft; Dust emissions; Military testing and training activities;

Experiments were conducted on a four-cylinder direct-injection diesel engine with part of the engine load taken up by fumigation methanol injected into the air intake of each cylinder to investigate the regulated and unregulated gaseous emissions and particulate emission of the engine under five engine loads at an engine speed of 1920 rev min−1. The fumigation methanol was injected to top up 10%, 20% and 30% of the engine load under different engine operating conditions.The experimental results show that at low engine loads, the brake thermal efficiency (BTE) decreases with increase in fumigation methanol; but at high engine loads, the BTE is not significantly affected by fumigation methanol. The fumigation methanol results in significant increase in hydrocarbon (HC), carbon monoxide (CO) and nitrogen dioxide (NO2) emissions, but decrease in nitrogen oxides (NOx). For the unregulated gaseous emissions, unburned methanol, formaldehyde and BTX (benzene, toluene and xylene) emissions increase but ethyne, ethene and 1,3-butadiene emissions decrease. Particulate mass and number concentrations also decrease with increase in fumigation methanol. A diesel oxidation catalyst (DOC) is found to reduce significantly most of the pollutants, including the air toxics, when the exhaust gas temperature is sufficiently high.
Keywords: Diesel engine; Methanol; Regulated emissions; Unregulated emissions; Particulate emissions;

Chemical characterization and source apportionment of fine and coarse particulate matter in Lahore, Pakistan by Elizabeth Stone; James Schauer; Tauseef A. Quraishi; Abid Mahmood (1062-1070).
Lahore, Pakistan is an emerging megacity that is heavily polluted with high levels of particle air pollution. In this study, respirable particulate matter (PM2.5 and PM10) were collected every sixth day in Lahore from 12 January 2007 to 19 January 2008. Ambient aerosol was characterized using well-established chemical methods for mass, organic carbon (OC), elemental carbon (EC), ionic species (sulfate, nitrate, chloride, ammonium, sodium, calcium, and potassium), and organic species. The annual average concentration (±one standard deviation) of PM2.5 was 194 ± 94 μg m−3 and PM10 was 336 ± 135 μg m−3. Coarse aerosol (PM10−2.5) was dominated by crustal sources like dust (74 ± 16%, annual average ± one standard deviation), whereas fine particles were dominated by carbonaceous aerosol (organic matter and elemental carbon, 61 ± 17%). Organic tracer species were used to identify sources of PM2.5 OC and chemical mass balance (CMB) modeling was used to estimate relative source contributions. On an annual basis, non-catalyzed motor vehicles accounted for more than half of primary OC (53 ± 19%). Lesser sources included biomass burning (10 ± 5%) and the combined source of diesel engines and residual fuel oil combustion (6 ± 2%). Secondary organic aerosol (SOA) was an important contributor to ambient OC, particularly during the winter when secondary processing of aerosol species during fog episodes was expected. Coal combustion alone contributed a small percentage of organic aerosol (1.9 ± 0.3%), but showed strong linear correlation with unidentified sources of OC that contributed more significantly (27 ± 16%). Brick kilns, where coal and other low quality fuels are burned together, are suggested as the most probable origins of unapportioned OC. The chemical profiling of emissions from brick kilns and other sources unique to Lahore would contribute to a better understanding of OC sources in this megacity.
Keywords: Aerosol; Source apportionment; Pakistan;

A comparative life-cycle energy and emissions (greenhouse gas, CO, NOX, SO2, PM10, and VOCs) inventory is created for three U.S. metropolitan regions (San Francisco, Chicago, and New York City). The inventory captures both vehicle operation (direct fuel or electricity consumption) and non-operation components (e.g., vehicle manufacturing, roadway maintenance, infrastructure operation, and material production among others). While urban transportation inventories have been continually improved, little information exists identifying the particular characteristics of metropolitan passenger transportation and why one region may differ from the next. Using travel surveys and recently developed transportation life-cycle inventories, metropolitan inventories are constructed and compared. Automobiles dominate total regional performance accounting for 86–96% of energy consumption and emissions. Comparing system-wide averages, New York City shows the lowest end-use energy and greenhouse gas footprint compared to San Francisco and Chicago and is influenced by the larger share of transit ridership. While automobile fuel combustion is a large component of emissions, diesel rail, electric rail, and ferry service can also have strong contributions. Additionally, the inclusion of life-cycle processes necessary for any transportation mode results in significant increases (as large as 20 times that of vehicle operation) for the region. In particular, emissions of CO2 from cement production used in concrete throughout infrastructure, SO2 from electricity generation in non-operational components (vehicle manufacturing, electricity for infrastructure materials, and fuel refining), PM10 in fugitive dust releases in roadway construction, and VOCs from asphalt result in significant additional inventory. Private and public transportation are disaggregated as well as off-peak and peak travel times. Furthermore, emissions are joined with healthcare and greenhouse gas monetized externalities to evaluate the societal costs of passenger transportation in each region. Results are validated against existing studies. The dominating contribution of automobile end-use energy consumption and emissions is discussed and strategies for improving regional performance given private travel's disproportionate share are identified.
Keywords: Automobile; Bus; Train; Ferry; Urban; Life-cycle assessment; Costs; Externalities;

Mass spectrometric study of secondary organic aerosol formed from the photo-oxidation of aromatic hydrocarbons by Kei Sato; Akinori Takami; Tasuku Isozaki; Toshihide Hikida; Akio Shimono; Takashi Imamura (1080-1087).
From measurements by an Aerodyne Aerosol Mass Spectrometer (AMS), secondary organic aerosol (SOA) formed in laboratory chambers is believed to be less oxidized than well-oxidized ambient organic aerosol (OA). However, the mass spectrum of SOA formed from the photo-oxidation of aromatic hydrocarbons has not been sufficiently studied by using AMS though these reactions are potential sources of urban SOA. In this study, we studied SOA formed from the photo-oxidation of seven aromatic hydrocarbons by using Time-of-Flight AMS. Strong mass signals from SOA were found at m/z 43 (m43) and 44 (m44) in all the experiments. The m44 to total organic aerosol mass ratio (m44/OA) increased with irradiation time. For example, the m44/OA ratio increased from 10.6% to 13.3% during irradiation for 11 h in an experiment with toluene. The average m44/OA ratios were determined to be 5.8–17.1% for all the experiments. The m44/OA decreased and the m43/OA increased with increasing number of alkyl substituents of precursor aromatic hydrocarbons. This is because low-reactive ketones are preferentially produced rather than aldehydes with increasing number of alkyl substituents. The m44/OA ratios of the benzene and monoalkylbenzene oxidation were 12.2–17.1% and were close to those of well-oxidized ambient OA. These findings are consistent with the hypothesis that the photo-oxidation of aromatic hydrocarbons is a potential source of urban SOA. In addition to oxygenated organic compounds, organic nitrogen oxides were also shown to be present in SOA by high-resolution mass spectra.
Keywords: Aromatic hydrocarbon; Secondary organic aerosol; Aerodyne time-of-flight aerosol mass spectrometer; Oxygenated organic aerosol; Particulate organic nitrate;

Temporal characteristics from continuous measurements of PM2.5 and speciation at the Taipei Aerosol Supersite from 2002 to 2008 by Shuen-Chin Chang; Charles C.-K. Chou; Chang-Chuan Chan; Chung-Te Lee (1088-1096).
This study uses monitoring data collected at the Taipei Aerosol Supersite from March 2002 to February 2008 to analyze characteristics such as seasonal fluctuations, diurnal variations, and photochemical-related variations of PM2.5 chemical compositions. The results indicate that the average of PM2.5 mass concentration in Taipei during this period is 30.3 ± 16.0 μg m−3. The highest average concentration of PM2.5 components is that of sulfate, which accounts for 21.1% of the PM2.5 mass, followed by organic carbon (OC) at 15.9%, nitrate at 5.8%, and elemental carbon (EC) at 5.4%. Concentrations of EC, OC, and nitrate have distinctive but similar seasonal fluctuations, which is highest in spring and lowest in fall. Sulfate concentration has less seasonal fluctuations, and the highest value appears during the fall. Similarly, concentrations of EC, OC, and nitrate have notable diurnal variations; however, the diurnal variation of sulfate concentration is not very apparent. These observation data show that EC, OC, and nitrate in PM2.5 in the Taipei metropolis come mainly from local emissions, while sulfate comes mainly from the regional transport of pollutants. This is likely because Taiwan is located on the lee zone of the Asian prevailing winds from fall to spring; its air quality is frequently affected by the transport of air pollutants from Mainland China. In addition, the extent of increase in aerosols is much higher than that of CO, indicating the formation of secondary aerosol when photochemical activity is strong. Based on six years of observation data, this study explores three potential scenarios to set up Taiwan's PM2.5 air quality standard (AQS). The analysis indicates that the optimum standard for 24-h air quality of PM2.5 should be around 50 μg m−3.
Keywords: PM2.5; Supersite; Secondary aerosol; Long-range transport; PM2.5 standard setup;

A method is developed for estimating the emission rates of contaminants into the atmosphere from multiple point sources using measurements of particulate material deposited at ground level. The approach is based on a Gaussian plume type solution for the advection–diffusion equation with ground-level deposition and given emission sources. This solution to the forward problem is incorporated into an inverse algorithm for estimating the emission rates by means of a linear least squares approach. The results are validated using measured deposition and meteorological data from a large lead–zinc smelting operation in Trail, British Columbia. The algorithm is demonstrated to be robust and capable of generating reasonably accurate estimates of total contaminant emissions over the relatively short distances of interest in this study.
Keywords: Pollutant dispersion; Gaussian plume; Particle deposition; Inverse problem;

Analysis of C1, C2, and C10 through C33 particle-phase and semi-volatile organic compound emissions from heavy-duty diesel engines by Z. Gerald Liu; Devin R. Berg; Victoria N. Vasys; Melissa E. Dettmann; Barbara Zielinska; James J. Schauer (1108-1115).
To meet increasingly stringent regulations for diesel engines, technologies such as combustion strategies, aftertreatment components, and fuel composition have continually evolved. The emissions reduction achieved by individual aftertreatment components using the same engine and fuel has been assessed and published previously (). The present study instead adopted a systems approach to evaluate the net effect of the corresponding technologies for model-year 2004 and 2007 engines. The 2004 engine was equipped with an exhaust gas recirculation (EGR) system, while the 2007 engine had an EGR system, a crankcase emissions coalescer, and a diesel particulate filter. The test engines were operated under the transient federal test procedure and samples were collected with a source dilution sampling system designed to stimulate atmospheric cooling and dilution conditions. The samples were analyzed for elemental carbon, organic carbon, and C1, C2, and C10 through C33 particle-phase and semi-volatile organic compounds. Of the more than 150 organic species analyzed, the largest portion of the emissions from the 2004 engine consisted of formaldehyde, acetaldehyde, and naphthalene and its derivatives, which were significantly reduced by the 2007 engine and emissions technology. The systems approach in this study simulates the operation of real-world diesel engines, and may provide insight into the future development of integrated engine technology. The results supply updated information for assessing the impact of diesel engine emissions on the chemical processes, radiative properties, and toxic components of the atmosphere.
Keywords: Organic compound emissions; Particulate matter emissions; Heavy-duty diesel engines; Aftertreatment technology; Diesel particulate filter; Chemical speciation;

The use of real-time monitoring data to evaluate major sources of airborne particulate matter by Stig Hellebust; Arnaud Allanic; Ian P. O'Connor; John C. Wenger; John R. Sodeau (1116-1125).
Real-time chemical measurements have been made as part of a field study of air quality in the city and harbour of Cork, Ireland. The data relate to the year 2008, with particular attention paid to the period between May and August. Eight air quality parameters were measured: NO, O3, NO2, SO2, EC, OC, particulate SO4 2− and PM2.5. The data have been used in a novel way involving wind and temporal averaging, along with Principal Component Analysis (PCA) and Positive Matrix Factorisation (PMF) methodologies to extrapolate major source contributions for PM2.5. It is demonstrated that continuous monitoring of standard air quality parameters, such as NO, NO2, SO2, along with EC, OC and particulate SO4 2−, can be used to provide relevant, cost-effective initial estimates of source contributions to ambient PM2.5 levels. It is also shown that the benefit of including OC and particulate SO4 2− in the monitoring protocol is considerable. Three major source groups of ambient PM2.5 mass in Cork were identified and quantified using this combined monitoring and modelling approach; road transport (19%), domestic solid fuel burning (14%) and oil-fired domestic and industrial boilers, including power generation plants (31%).
Keywords: Air quality monitoring; PM2.5; Source apportionment; Positive matrix factorisation; Road transport emissions; Combustion;

Modelling aerosol number distributions from a vehicle exhaust with an aerosol CFD model by B. Albriet; K.N. Sartelet; S. Lacour; B. Carissimo; C. Seigneur (1126-1137).
Vehicular traffic contributes significantly to the aerosol number concentrations at the local scale by emitting primary soot particles and forming secondary nucleated nanoparticles. Because of their potential health effects, more attention is paid to the traffic induced aerosol number distributions.The aim of this work is to explain the phenomenology leading to the formation and the evolution of the aerosol number distributions in the vicinity of a vehicle exhaust using numerical modelling. The emissions are representative of those of a light-duty diesel truck without a diesel particle filter. The atmospheric flow is modelled with a computational fluid dynamics (CFD) code to describe the dispersion of pollutants at the local scale. The CFD code, coupled to a modal aerosol model (MAM) describing the aerosol dynamics, is used to model the tailpipe plume of a vehicle with emissions corresponding to urban driving conditions. On the basis of available measurements in , three surrogate species are chosen to treat the semi-volatile organic compounds in the emissions.The model simulates the formation of the aerosol distribution in the exhaust plume of a vehicle as follows. After emission to the atmosphere, particles are formed by nucleation of sulphuric acid and water vapour depending strongly on the thermodynamic state of the atmosphere and on the dilution conditions. The semi-volatile organic compounds are critical for the rapid growth of nanoparticles through condensation. The semi-volatile organic compounds are also important for the evolution of primary soot particles and can contribute substantially to their chemical composition.The most influential parameters for particle formation are the sulphur fuel content, the semi-volatile organic emissions and also the mass and initial diameter of the soot particles emitted. The model is able to take into account the complex competition between nucleation, condensation and dilution, as well as the interactions among the different aerosol modes. This type of model is a useful tool to better understand the dynamics leading to the formation of traffic induced aerosol distributions. However, some key issues such as the turbulence in the exhaust plume and in the wake of the car, the magnitude and chemical composition of semi-volatile organic emissions and the possible nucleation of organic species need to be investigated further to improve our understanding of ultrafine particle formation.
Keywords: Traffic emission; CFD simulation; Number distribution; Semi-volatile organic compounds (SVOC); Ultrafine particles; Nanoparticles;

There is no specific number of samples that ensure a satisfactory PMF analysis. The statement made in this paper with respect to a specific number of samples is only applicable to this data set and should not be applied to any other data set.
Keywords: Factor analysis; Number of samples;