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Atmospheric Environment (v.45, #15)

Editorial board (pp. i).

Estimation of monthly values of atmospheric turbidity using measured values of global irradiation and estimated values from CSR and Yang Hybrid models. Study case: Argentina by Germán A. Salazar (pp. 2465-2472).

For ten sites in Argentina, monthly average Ångström turbidity coefficient β values were estimated using mean monthly global solar irradiation values measured at these sites from the former Argentinean radiometric network REDSOL. The values of the horizontal direct and diffuse components of the global irradiation were estimated using the Yang Hybrid model (YHM) and, to determine the representativeness of those results, they were compared to values from the SWERA database which uses the CSR model, developed by NREL, to make estimates. An inconsistency in the estimated values of the diffuse component was detected, therefore a new expression for that component was proposed, generating a corrected version of the YHM (CYHM). The turbidity coefficient β is considered an independent variable in the equation that estimates the direct transmittance and the values that forces an exact correlation between the measured monthly average global irradiance values with those estimated with the CYHM are considered representative for each site since the RMSE between the monthly global irradiation values of SWERA and CYHM is 11.7%, this value being very close to that found by the designers of the CSR model (10%) when they tested it with meteorological data from USA. The monthly average value estimates of turbidity coefficient β show expected behavior, with values varying according to the season of the year.► A new method is proposed to estimate monthly average turbidity values from global irradiance data. ► The proposed method includes the Correct Yang Hybrid Model (CYHM). ► A difference of 11.7% was obtained between CYHM estimates and SWERA database values. ► It is assumed that the error in the turbidity coefficient values is also low.

Keywords: Global solar irradiation; CSR; Yang Hybrid model; Ångström turbidity coefficient; Argentina

Molecular composition and size distribution of sugars, sugar-alcohols and carboxylic acids in airborne particles during a severe urban haze event caused by wheat straw burning by Gehui Wang; Chunlei Chen; Jianjun Li; Bianhong Zhou; Mingjie Xie; Shuyuan Hu; Kimitaka Kawamura; Yan Chen (pp. 2473-2479).

Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m⁻³) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2–20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (>2.1 μm) with respect to the haze and non-haze samples, but a large difference in the fine fraction (<2.1 μm) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes.► WSOCs during the haze event were mainly from the field burning of wheat straw. ► WSOCs in the event were 2–20 times more abundant than those in the non-event. ► A sharp increased WSOC in fine mode was found during the hazy days. ► Succinic acid is preferably formed during biomass burning emission transport.

Keywords: Water-soluble organic compounds; Biomass burning; Atmospheric aerosols; Composition and size distribution; Levoglucosan and succinic acid

Atmospheric gaseous elemental mercury (GEM) over a coastal/rural site downwind of East China: Temporal variation and long-range transport by Zhijia Ci; Xiaoshan Zhang; Zhangwei Wang; Zhenchuan Niu (pp. 2480-2487).

Although much attention has been paid to the mercury pollution in China, limited field studies have been conducted to explore the atmospheric behavior of mercury. To investigate the temporal variation and long-range transport of atmospheric gaseous elemental mercury (GEM or Hg(0)), the GEM measurements covering four different seasons were performed at a coastal/rural site of the Yellow Sea downwind of East China. Hourly mean concentrations of GEM measured by RA–915+ mercury analyzer over the entire study (four different time periods between July 2007 and May 2009) were 2.31 ± 0.74 ng m⁻³ with a range of 1.12–7.01 ng m⁻³. The results showed moderate seasonal variations with high levels in cold seasons (winter: 2.53 ± 0.77 ng m⁻³ and spring: 2.34 ± 0.54 ng m⁻³) and low levels in warm seasons (summer: 2.28 ± 0.82 ng m⁻³ and fall: 2.16 ± 0.84 ng m⁻³). Over the each campaign a diurnal variation of GEM was observed consistently with peak levels in daytime and low levels in late night and early morning. The pollution rose and NOAA–HYSPLIT back-trajectory model analyses indicated that the elevated GEM was transported to the sampling site from the regional sources of East China and Korea peninsula–Japan. Air masses originated from the East China Sea and the regions of Continental East Asia with low emission strengths of atmospheric mercury (e.g., the east Russia, the north Inner Mongolia and the Bohai Sea) showed the decreased GEM levels.► Elevated GEM levels were observed at a coastal/rural site downwind of East China. ► GEM showed high levels in cold seasons and low levels in warm seasons. ► GEM showed peak levels in daytime and low levels in late night and early morning. ► Complicated patterns of GEM transport from different source regions were recorded.

Keywords: Gaseous elemental mercury (GEM); Temporal variation; Seasonal/diurnal variation; Long-range transport (LRT); Yellow Sea; China

Cloud residues and interstitial aerosols from non-precipitating clouds over an industrial and urban area in northern China by Weijun Li; Peiren Li; Guode Sun; Shengzhen Zhou; Qi Yuan; Wenxing Wang (pp. 2488-2495).

Most studies of aerosol–cloud interactions have been conducted in remote locations; few have investigated the characterization of cloud condensation nuclei (CCN) over highly polluted urban and industrial areas. The present work, based on samples collected at Mt. Tai, a site in northern China affected by nearby urban and industrial air pollutant emissions, illuminates CCN properties in a polluted atmosphere. High-resolution transmission electron microscopy (TEM) was used to obtain the size, composition, and mixing state of individual cloud residues and interstitial aerosols. Most of the cloud residues displayed distinct rims which were found to consist of soluble organic matter (OM). Nearly all (91.7%) cloud residues were attributed to sulfate-related salts (the remainder was mostly coarse crustal dust particles with nitrate coatings). Half the salt particles were internally mixed with two or more refractory particles (e.g., soot, fly ash, crustal dust, CaSO₄, and OM). A comparison between cloud residues and interstitial particles shows that the former contained more salts and were of larger particle size than the latter. In addition, a somewhat high number scavenging ratio of 0.54 was observed during cloud formation. Therefore, the mixtures of salts with OMs account for most of the cloud-nucleating ability of the entire aerosol population in the polluted air of northern China. We advocate that both size and composition – the two influential, controlling factors for aerosol activation – should be built into all regional climate models of China.► Most cloud residues displayed distinct rims including soluble organic matter. ► The mixtures of salts with organics account for most cloud-nucleating ability. ► Aerosol size and composition should be included in cloud-climate models of China.

Keywords: Cloud condensation nuclei; Aerosol activation; Interstitial aerosol; Mt. Tai; Transmission electron microscopy

Short-term secondary organic carbon estimations with a modified OC/EC primary ratio method at a suburban site in Madrid (Spain) by Javier Plaza; Begoña Artíñano; Pedro Salvador; Francisco J. Gómez-Moreno; Manuel Pujadas; Casimiro A. Pio (pp. 2496-2506).

A time series of more than two years of continuous measurements of EC, OC and TC obtained with a Rupprecht and Patashnick (R&P) thermal analyzer at a suburban site in Madrid has been evaluated in this work. Correction factors obtained from intercomparison exercises with thermo-optical methods were applied to the original measurements. Corrected OC and EC mean values are 3.7 and 1.3 μg m⁻³ respectively. The highest individual values have been recorded in winter. No seasonal variation has been observed in OC, whereas a slight decrease of EC is observed in summer, leading to higher OC/EC ratios. The mean value of the OC/EC ratio is 4.9. Daily patterns show maximum EC and OC associated to traffic rush hours, with a delay of the OC peak related to the formation of SOC. Daily oscillation is more pronounced in winter. Hourly estimations of SOC production have been obtained by the primary OC/EC ratio approach, after discounting the OC, EC background contamination. A mean primary ratio value of 0.59 has been used for SOC short-term estimations throughout the entire time period. As expected, the highest SOC production is observed in summer, related to the increasing in photochemical activity, which also influences daily patterns and the time of the daily SOC maximum. In summer the daily SOC production ranges from 80 to 92%, whereas in the winter months it varies from 70 to 84%. These SOC estimations do not discount primary biogenic or natural contributions to OC and are therefore maximum values.► Short-term secondary organic carbon estimates have been obtained. ► A modified OC/EC primary ratio method is proposed. ► Seasonal variations are analyzed and interpreted. ► Secondary organic carbon contribution is higher in spring and summer. ► Other sources that traffic of secondary organic carbon should not be discarded.

Keywords: Organic carbon; Elemental carbon; Urban aerosol; Primary OC/EC ratio; SOC apportionment

Characterizing local traffic contributions to particulate air pollution in street canyons using mobile monitoring techniques by Leonard M. Zwack; Christopher J. Paciorek; John D. Spengler; Jonathan I. Levy (pp. 2507-2514).

Traffic within urban street canyons can contribute significantly to ambient concentrations of particulate air pollution. In these settings, it is challenging to separate within-canyon source contributions from urban and regional background concentrations given the highly variable and complex emissions and dispersion characteristics. In this study, we used continuous mobile monitoring of traffic-related particulate air pollutants to assess the contribution to concentrations, above background, of traffic in the street canyons of midtown Manhattan. Concentrations of both ultrafine particles (UFP) and fine particles (PM_2.5) were measured at street level using portable instruments. Statistical modeling techniques accounting for autocorrelation were used to investigate the presence of spatial heterogeneity of pollutant concentrations as well as to quantify the contribution of within-canyon traffic sources. Measurements were also made within Central Park, to examine the impact of offsets from major roadways in this urban environment. On average, an approximate 11% increase in concentrations of UFP and 8% increase in concentrations of PM_2.5 over urban background was estimated during high-traffic periods in street canyons as opposed to low traffic periods. Estimates were 8% and 5%, respectively, after accounting for temporal autocorrelation. Within Central Park, concentrations were 40% higher than background (5% after accounting for temporal autocorrelation) within the first 100m from the nearest roadway for UFP, with a smaller but statistically significant increase for PM_2.5. Our findings demonstrate the viability of a mobile monitoring protocol coupled with spatiotemporal modeling techniques in characterizing local source contributions in a setting with street canyons.► In complex urban terrain local traffic contributes to ambient concentrations. ► Monitoring and modeling quantified this traffic and air pollution relationship. ► An 8–11% increase in UFP and 5–8% increase in PM_2.5 over background was observed. ► Sharp decreases in UFP over the first 100m into Central Park were observed.

Keywords: Ultrafine particles; Fine particulate matter; Urban air quality; Mobile measurements; Regression; Mobile sources; New York City

Nitration of particle-associated PAHs and their derivatives (nitro-, oxy-, and hydroxy-PAHs) with NO₃ radicals by Yang Zhang; Bo Yang; Jie Gan; Changgeng Liu; Xi Shu; Jinian Shu (pp. 2515-2521).

The heterogeneous reactions of typical polycyclic aromatic hydrocarbons (PAHs) and their derivatives (nitro-, oxy-, and hydroxy-PAHs) adsorbed on azelaic acid particles with NO₃ radicals are investigated using a flow-tube reactor coupled to a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The mono-nitro-, di-nitro-, and poly-nitro-products from successive nitro-substitution reactions of PAHs and their derivatives are observed in real time with VUV-ATOFMS. 9-Nitroanthracene, anthraquinone, anthrone, 9,10-dinitroanthracene, 2-, 4-, and 9-nitrophenanthrene, 1-nitropyrene, 1,3-, 1,6-, and 1,8-dinitropyrene, 7-nitrobenzo[ a]anthracene, and benzo[ a]anthracene-7,12-dione are identified by GC/MS analysis of the reaction products of PAHs and their derivatives coated on the inner bottom surface of the conical flasks with NO₃ radicals. Other oxygenated products are tentatively assigned. 1-Nitropyrene is the only mono-nitrated product detected in the reaction of surface-bound pyrene with gas-phase NO₃ radicals. This phenomenon is different from what has been observed in previous studies of the gas-phase pyrene nitration, showing that 2-nitropyrene is the sole nitration product. The experimental results may reveal the discrepancies between the heterogeneous and homogeneous nitrations of pyrene.► The reactions of aerosol-associated PAHs and their derivatives with NO₃ radicals are carried out. ► The particle-phase reactants and their reaction products are analyzed in real time. ► Nitrated and oxygenated products are observed. ► The identification of the products by GC/MS is performed.

Keywords: Heterogeneous reaction; NO; ₃; radicals; PAHs; Aerosol mass spectrometry

Model evaluation of roadside barrier impact on near-road air pollution by Gayle S.W. Hagler; Wei Tang; Matthew J. Freeman; David K. Heist; Steven G. Perry; Alan F. Vette (pp. 2522-2530).

Roadside noise barriers are common features along major highways in urban regions and are anticipated to have important effects on near-road air pollution through altering the dispersion of traffic emissions and resulting downstream concentrations. A 3-dimensional computational fluid dynamics (CFD) 6-lane road model has been developed to simulate roadside barrier effects on near-road air quality and evaluate the influence of key variables, such as barrier height and wind direction. The CFD model matches an existing wind tunnel road model and comparison with the wind tunnel data guided the selection of the optimal turbulence model (Realizeable k– ɛ turbulence model with a Schmidt number of 1.0). Under winds perpendicular to the road, CFD model simulations show that roadside barriers reduce the concentration of an inert gaseous tracer ( χ), relative to a no-barrier situation, vertically up to approximately half the barrier height and at all horizontal distances from the road. At 20m (3.3 H, where H=6m) from the road, barriers of heights ranging from 0.5 H to 3.0 H reduce the maximum concentrations by 15–61% relative to a no-barrier case, with the location of the maximum shifted to occur near the top of the barrier. The near-road reduction comes at a penalty for on-road air pollutant concentrations: on-road pollution is projected to increase by a factor of 1.1–2.3 corresponding to barriers ranging from 0.5 H to 3.0 H. When the noise barrier is downwind of the road, a stagnant zone is formed behind the barrier and minor road emissions (e.g., 5% of the highway emissions strength) in this zone, such as a moderately traveled service road, have a magnified effect on concentrations immediately behind the barrier. Wind direction and barrier termination also play a critical role, with a spill-over of accumulated emissions upwind of the barrier strongly increasing near-road concentrations at one end of the barrier. These results imply that roadside barriers may mitigate near-road air pollution, although local meteorology, the barrier structure, and the degree of lee-side emission sources are critical factors determining the outcome.► Traffic emissions dispersion in the presence of a roadside barrier is evaluated using a computational fluid dynamics model. ► Under crosswind conditions, barriers reduce downwind near-road maximum concentrations, but increase on-road concentrations. ► Minor emissions (e.g., service road) in the stagnant zone downwind of a barrier can increase near-road pollution levels. ► Oblique winds can transport accumulated on-road emissions around the edge of a barrier and create a local high concentration zone.

Keywords: Near-road; Barriers; Traffic; Air pollution; CFD; Modeling

Identifying pollutant source directions using multiple analysis methods at a rural location in New York by Min-Suk Bae; James J. Schwab; Wei-Nai Chen; Chuan-Yao Lin; Oliver V. Rattigan; Kenneth L. Demerjian (pp. 2531-2540).

We identify the directionality of sources contributing to observed pollutant concentrations at a rural site through the use of the analysis methods of Conditional Probability Function (CPF) and the Source Direction Probability (SDP). Input data consists of hourly averaged PM_2.5 mass, Organic Mass (OM) from Organic Carbon (OC), optical Elemental Carbon (optical EC), SO₂, CO, NOy, O₃ concentrations and metrological data from Pinnacle State Park site in rural New York State for the period of Dec 2004 to Dec 2008. These measured pollutants are coupled with on-site wind data to identify the directionality of the sources; which are then compared to known stationary source locations from the EPA Air Data web site. Although the CPF plot of the O₃ showed no distinct directionality source area, the Pinnacle State Park site was frequently impacted by plumes of relatively high PM_2.5 mass, SO₂, CO, NOy, optical EC and OM concentrations. Further analysis of the enhanced pollution occurrence frequency from the eastern sector revealed two peaks in the time-of-day distribution of elevated CO, NOy, and optical EC, which provides additional information on the sources. This contrasts with the enhanced pollution occurrence frequency from the south for CO, OM, and optical EC, which shows a single morning peak in its time-of-day distribution and indicates a somewhat more distant, but common source for these carbon-containing pollutants. PM_2.5 mass corresponds to the source areas related to emission facilities listed in the EPA Emissions Inventory, which is further confirmed by correlation and analysis of aerosol optical depth (AOD) data from Moderate-resolution Imaging Spectrometer (MODIS) on board Terra and Aqua satellites. We present evidence that most of the high pollution episodes likely arise from emission sources located several hundred kilometers from the site, indicating mid-long range transport of pollutants to this location.► We identify the directionality of pollutant sources that contribute to a rural location in New York State. ► Combined multiple analysis methods indicate episodes were due to mid-long range transportation. ► In spring and fall, the potential sources could be in the middle-east regions of Pennsylvania. ► For winter, the middle and the middle-east regions of Pennsylvania can be major contributors. ► For summer, the sources clearly originating from middle-west regions of Pennsylvania.

Keywords: Source; Direction; CPF; SDP; AOD

The winter effect on formation of PCDD/Fs in Guangzhou by vehicles: A tunnel study by Yunyun Deng; Pingan Peng; Man Ren; Jianzhong Song; Weilin Huang (pp. 2541-2548).

Prior studies showed that the polychlorinated dibenzo- p-dioxin and dibenzofuran (PCDD/F) concentrations in the atmosphere are much higher in the winter than in the summer. This so called winter effect was explained via meteorology-dependent factors such as dispersion, mixing and photo chemical degradation or home heating related formation of PCDDs/Fs. In this study, we took vehicle emission as an example to investigate winter effect on PCDD/Fs formation by fossil fuel combustion. We hypothesized that vehicle emission of PCDDs/Fs may be elevated in the winter season due to the promoted supplies of Cl⁻ (via particular matter) in winter. We collected particulate and gaseous samples from the Pearl River Tunnel and its adjacent open air during spring/summer and winter seasons. Chemical analyses of the tunnel samples showed that the PCDD/F concentrations in the tunnel ranged from 18.6 to 20.4pgm⁻³ (1.28–1.39pgI-TEQm⁻³) in the winter, which were 3–5 times higher than in the spring/summer. In the open atmosphere adjacent to the tunnel, the PCDD/F concentrations were much lower than in the tunnel; e.g., approximately one fifth of the tunnel air concentrations during the winter. The emission factors (EFs) calculated based on the tunnel data were 3440 (or 230 I-TEQ) and 1580 (or 27.8 I-TEQ)pgkm⁻¹vehicle⁻¹ in winter and spring/summer season, respectively. The much higher PCDD/F concentrations in the tunnel air and much greater EF value during the winter are likely related to higher content of Cl⁻ associated with small size particulates. This suggests that the winter effect observed in the open atmosphere is not only caused by meteorology-dependent factors and home heating, but also may partly results from much greater PCDD/F formation rates during the combustion processes of fossil fuels such as gasoline- and diesel-fuel in the winter.► This is the first research about PCDD/Fs emission in the tunnel of China. ► The winter effect of PCDD/Fs was firstly observed in the tunnel study. ► Different homolog distributions of PCDDs/Fs were observed in our tunnel study. ► The data from our research provides a new alternative explanation for winter effect.

Keywords: PCDDs/Fs; Vehicle; Winter effect; Emission factor

Simulation of regional dust and its effect on photochemistry in the Mexico City area during MILAGRO experiment by Zhuming Ying; Xuexi Tie; Sasha Madronich; Guohui Li; Steven Massie (pp. 2549-2558).

Dust particles have important effects on solar radiation, climate, and photochemistry in the troposphere. Dust events were observed from March 16 to 20, 2006 in the Mexico City (MC) area during the MILAGRO (Megacity Initiative: Local and Global Research Observations) field experiment. In order to study the effects of dust aerosols on total aerosol mass concentrations and photochemistry, a regional chemical/dynamical model (Weather Research and Forecasting Chemical model version 3 – WRF/Chem-v3) was used in this study, and a dust module was implemented in the model. Analysis of model and observational data suggests that the large area of coastal dry lands to the northeast of MC is an important source of dust particles for the entire MC area. The simulations of both PM_2.5 (total particle mass with radius less than 2.5 μm) and PM₁₀ (total particle mass with radius less than 10 μm) concentrations are more consistent with observations than the results of the model without the dust module. During this dust period (March 16–20, 2006), the simulated dust aerosol mass accounts for about 70% of the total PM₁₀ aerosol mass concentrations, with a strong diurnal variation. The results also suggest that dust aerosols have important effects on actinic fluxes and therefore photochemistry, especially on hydroxyl radical (OH) and ozone (O₃) concentrations, in the MC area and the surrounding region. The dust particles decrease the photochemical production of OH, with a maximum reduction of 60% in the dust source region (northeast of the MC area). Near the city area, the reduction of OH concentrations is about 5–20%. The strongest effects on O₃ concentrations are near MC, where the maximum reduction of O₃ is about 10 ppbv. In the dust source region, O₃ concentrations are reduced by about 3–5 ppbv.► Dust aerosol is important in the Mexico City area on dusty days. ► Large dry lands to northeast of MC is an important dust source for all MC area. ► Dust produces a significant reduction of the surface OH and O₃ in the MC region.

Keywords: Dust; WRF/Chem; Photochemistry; Mexico City

The influence of fog and airmass history on aerosol optical, physical and chemical properties at Pt. Reyes National Seashore by Carl M. Berkowitz; Larry K. Berg; Xiao-Ying Yu; M. Lizabeth Alexander; Alexander Laskin; Rahul A. Zaveri; B. Thomas Jobson; Elisabeth Andrews; John A. Ogren (pp. 2559-2568).

This paper presents an analysis of the aerosol chemical composition, optical properties and size distributions for a range of conditions encountered during a field measurement campaign conducted between July 7–29, 2005 at Point Reyes National Seashore, north of San Francisco, CA. The fractional mass loading derived from hourly measurements of an Aerodyne Mass Spectrometer (AMS) during this period are compared with filter-pack measurements from the Pt. Reyes IMPROVE station with good agreement found between the two if it assumed that chloride is primarily from large sea-salt particles (not measured by the AMS). During the first half of the campaign (July 7–17), conditions at the site were largely maritime while flow during the second half of the campaigns (July 18–29) was influenced by a thermal trough that added a cyclonic twist to the incoming marine air, bringing it from the south with a more extensive over-land trajectory. Neither flow regime was associated with air coming from the San Francisco Bay area to the south. The AMS measurements are partitioned into clear and foggy conditions which are then used to calculate the equivalent molar ratio of ammonium to the sum of sulfate, nitrate and chloride. Ratios calculated from measurements made before the onset of the thermal trough on July 18th were associated with acidic or near-neutral particles. Measurements made after July 18th yield ratios that appear to have excess ammonium. Model calculations of the equilibrium gas-phase mixing ratio of NH₃ suggest very high values which we attribute to agricultural practices within the park. Reported as an incidental finding is evidence for the cloud droplet activation of large particles (D_P > 0.2 μm) with a corresponding reduction in the single scattering albedo of the non-activated particles, followed by a return in the particle size spectrum to the pre-fog conditions immediately afterwards.► Aerosol measurements are presented for July, 2005 at Pt. Reyes National Seashore. ► Mass spec observations are compared with measurements from the local IMPROVE site. ► The California Thermal Trough is shown to influence particle composition. ► Aerosol scattering and mass loading are reported under clear and foggy conditions. ► Changes in particle size spectrum under clear and foggy conditions are reported.

Keywords: Aerodyne mass spectrometer; Air quality; Atmospheric aerosol; Ammonia; Ammonium; IMPROVE; Dairy farm; Pt. Reyes National Seashore; Sulfate; Scavenging; Thermal trough

Limited potential of crop management for mitigating surface ozone impacts on global food supply by Edmar Teixeira; Guenther Fischer; Harrij van Velthuizen; Rita van Dingenen; Frank Dentener; Gina Mills; Christof Walter; Frank Ewert (pp. 2569-2576).

Surface ozone (O₃) is a potent phytotoxic air pollutant that reduces the productivity of agricultural crops. Growing use of fossil fuel and climate change are increasing O₃ concentrations to levels that threaten food supply. Historically, farmers have successfully adapted agricultural practices to cope with changing environments. However, high O₃ concentrations are a new threat to food production and possibilities for adaptation are not well understood. We simulate the impact of ozone damage on four key crops (wheat, maize, rice and soybean) on a global scale and assess the effectiveness of adaptation of agricultural practices to minimize ozone damage. As O₃ concentrations have a strong seasonal and regional pattern, the adaptation options assessed refer to shifting crop calendars through changing sowing dates, applying irrigation and using crop varieties with different growth cycles. Results show that China, India and the United States are currently by far the most affected countries, bearing more than half of all global losses and threatened areas. Irrigation largely affects ozone exposure but local impacts depend on the seasonality of emissions and climate. Shifting crop calendars can reduce regional O₃ damage for specific crop-location combinations (e.g. up to 25% for rain-fed soybean in India) but has little implication at the global level. Considering the limited benefits of adaptation, mitigation of O₃ precursors remains the main option to secure regional and global food production.► Global modeling of surface ozone (O₃) damage for maize, wheat, rice and soybean crops. ► We evaluate benefits of adapting crop management to reduce yield losses. ► Changes in sowing date, crop variety and irrigation had little global implication.► At regional level adaptive options may be effective. ► Security of food supply may benefit more from mitigating emission of O₃ precursors.

Keywords: AEZ; Air quality; Climate adaptation; Food security; Ozone pollution; Mitigation

Key volatile organic compounds emitted from swine nursery house by H.Q. Yao; H.L. Choi; K. Zhu; J.H. Lee (pp. 2577-2584).

This study was carried out to quantify the concentration and emission levels of key volatile organic compounds (VOCs) – sulfides, indolics, phenolics and volatile fatty acids (VFA) – emitted from swine nursery house, and assess the effect of microclimate (including temperature, relative humidity and air speed) on the key odorous compounds. Samples were collected from the Experimental Farm of Seoul National University in Suwon, South Korea. And the collection took place for four seasons and the sampling time was fixed at 10:30 in the morning. The application of one-way ANOVA and Bonferroni t analyses revealed that, most of the odorous compound concentrations, such as dimethyl sulfide (DMS), dimethyl disulfide (DMDS), indole, p-cresol and all the volatile fatty acids were lowest during the summer ( P<0.01). Meanwhile, negative correlations were observed between temperature and odorants, as well as air speed and odorants. A possible reason was that high ventilation transferred most of the odors out of the house during the summer. From the whole year data, non-linear multiple regressions were conducted and the equations were proposed depending upon the relationships between microclimate parameters and odorous compounds. The equations were applied in hope of easily calculating the concentrations of the odorous compounds in the commercial farms. The results obtained in this study should be used for reducing the volatile organic compounds by controlling microclimate parameters and also could be helpful in setting a guideline for good management practices in nursery house.► We carry the study in an confined swine nursery house. ► We quantify the concentration and emission levels of key VOCs. ► We assess the effect of microclimate on the VOCs. ► Equations are proposed for evaluating VOCs through microclimate parameters. ► The result should be useful for reducing the VOCs by controlling the microclimate.

Keywords: Confined nursery house; VOCs; Emission; Microclimate

Combining regression analysis and air quality modelling to predict benzene concentration levels by Ch. Vlachokostas; Ch. Achillas; E. Chourdakis; N. Moussiopoulos (pp. 2585-2592).

State of the art epidemiological research has found consistent associations between traffic-related air pollution and various outcomes, such as respiratory symptoms and premature mortality. However, many urban areas are characterised by the absence of the necessary monitoring infrastructure, especially for benzene (C₆H₆), which is a known human carcinogen. The use of environmental statistics combined with air quality modelling can be of vital importance in order to assess air quality levels of traffic-related pollutants in an urban area in the case where there are no available measurements. This paper aims at developing and presenting a reliable approach, in order to forecast C₆H₆ levels in urban environments, demonstrated for Thessaloniki, Greece. Multiple stepwise regression analysis is used and a strong statistical relationship is detected between C₆H₆ and CO. The adopted regression model is validated in order to depict its applicability and representativeness. The presented results demonstrate that the adopted approach is capable of capturing C₆H₆ concentration trends and should be considered as complementary to air quality monitoring.► Establishing statistical associations between air pollutants. ► Linear relationship between benzene and common traffic-related air pollutants. ► Regression model C₆H₆ = f(CO), validated on a number of stations in Europe. ► Development of a reliable approach in order to forecast C₆H₆ levels in urban areas.

Keywords: Air pollution; Regression analysis; Air quality modelling; Benzene; Traffic; Urban areas

Enhanced NO₂ at Okinawa Island, Japan caused by rapid air-mass transport from China as observed by MAX-DOAS by H. Takashima; H. Irie; Y. Kanaya; H. Akimoto (pp. 2593-2597).

Since March 2007, continuous NO₂ profile observations have been performed using ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at Cape Hedo (26.87°N, 128.25°E) on Okinawa Island, Japan. NO₂ observations show particularly low values of less than 0.3 ppbv at 0–1 km in most cases during the northern summer, whereas higher concentrations of more than 1 ppbv were occasionally observed during winter and spring. Trajectory analysis using meteorological analysis data showed that the high NO₂ concentrations were caused mainly by rapid air-mass transport in the marine boundary layer, with strong westerly winds bringing the air mass from coastal China to the study site within ∼24 h. Such rapid transport is a major cause of NO₂ variations at Cape Hedo, even though the region is located approximately 700 km from China.► NO₂ profile observations have been performed by MAX-DOAS at Cape Hedo, Japan. ► Higher NO₂ concentrations were occasionally observed during winter and spring. ► The high concentrations were caused by rapid air-mass transport from coastal China.

Keywords: Nitrogen dioxide; MAX-DOAS; Long-range transport

Discussion of “Tropospheric ozone variability over the Iberian Peninsula Atmospheric Environment” by by A.T.J. de Laat (pp. 2598-2599).

Reply to discussion of “Tropospheric ozone variability over the Iberian Peninsula Atmospheric Environment” by by Pavan S. Kulkarni; D. Bortoli; R. Salgado; M. Antón; M.J. Costa; A.M. Silva (pp. 2600-2602).

In the discussion paper on our article (), de Laat has criticized TOR methodology and TOR data and thus questioned the validity of the findings. He has also pointed out the fact that the authors may have used the OMI/MLS data. In this reply to the discussion, the clarifications and references given herewith endeavour to undoubtedly answer the questions posed by de Laat on TOR methodology and on TOR data and thus proving that the findings of are scientifically justified and therefore entirely valid. Furthermore, reasons were presented to justify the non use of the OMI/MLS data.

Keywords: TOR methodology; TOR data

Real-world PM, NO_x, CO, and ultrafine particle emission factors for military non-road heavy duty diesel vehicles by Dongzi Zhu; Nicholas J. Nussbaum; Hampden D. Kuhns; M.-C. Oliver Chang; David Sodeman; Hans Moosmüller; John G. Watson (pp. 2603-2609).

Training on US military bases involves nonroad diesel vehicles with emissions that can affect base personnel, nearby communities, and attainment of air quality standards. Nonroad diesel engines contribute 44% of diesel PM and 12% of total NO_x emissions from mobile sources nationwide. Although military sector fuel use accounts for only ≈0.4% of distillate fuel use in US, emissions factors measured for these engines improve the representation of the relatively small (as compared to onroad sources) database of nonroad emission factors. Heavy-duty multi-axle, all-wheel drive military trucks are not compatible with regular single-axle dynamometers and their emissions cannot be measured under standard laboratory conditions. We have developed a novel in-plume technique to measure in-use emissions from vehicles with elevated stack. Real-world gaseous and particulate matter (PM) emission factors (EFs) from ten 7-ton 6-wheel drive trucks and two 8-wheel drive heavy tactical Logistics Vehicle System (LVS) vehicles were measured using in-plume sampling. The EFs of these trucks are comparable to those of onroad trucks while the PM EFs of 2-stroke LVS are ≈10 times higher than those of onroad vehicles. Lower EC/PM ratio was observed for LVS compared with MTVR. PM number emission factors were 5.9 × 10¹⁴ particles km⁻¹ for the trucks and 2.5 × 10¹⁶ particles km⁻¹ for the LVSs, three orders of magnitude higher than the proposed European Union standard of 6 × 10¹¹ particles km⁻¹. The EFs sampled can be extended to engines used in the broader nonroad sector including agriculture and mining and used as inputs to the NONROAD model.► Novel in-plume measurement of in-use emissions from heavy-duty nonroad vehicles. ► PM EFs of diesel 2-stroke engines are ≈10 times higher than 4-stroke engines. ► Nonroad trucks EFs are similar to those of onroad trucks of similar size. ► Measured EFs can be used as inputs for EPA’s NONROAD model where data is sparse.

Keywords: Nonroad; Diesel; Emission factor; Military; Real-world emissions

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Atmospheric Environment (v.45, #15)