Atmospheric Environment (v.44, #9)

Elevated biogenic sulphur dioxide concentrations over the North Atlantic by Alison Michelle Seguin; Ann-Lise Norman; Sarah Eaton; Morie Wadleigh; Sangeeta Sharma (1139-1144).
Elevated biogenic SO2 from the oxidation of dimethylsulphide (DMS) in the marine atmosphere was measured over the North Atlantic Ocean in spring and summer 2003. Stable isotope apportionment was used to distinguish between anthropogenic and biogenic SO2 in the marine atmosphere south of Greenland. Atmospheric DMS measurements were within range of previous studies. Biogenic SO2 concentrations were as high as 82 nmol m−3 (spring geometric mean: 4 nmol m−3, σ = 17; summer geometric mean 7 nmol m−3, σ = 19) and are the highest reported values for marine biogenic SO2 in the literature. Elevated biogenic SO2 was found in air masses influenced by anthropogenic pollutants during the summer. This indicates that anthropogenic pollutants may affect the fate of oceanic emissions of sulphur compounds in the atmosphere favoring the formation of cloud condensation nuclei.
Keywords: SO2; DMS oxidation; Sulphur isotope;

Uptake of acetone, acetaldehyde and ethanol in cold sulfuric acid solutions containing organic material: Carbon accretion mechanisms by Margaret B. Williams; Rebecca R.H. Michelsen; Jessica L. Axson; Laura T. Iraci (1145-1151).
The solubilities of acetone, ethanol and acetaldehyde in cold ternary solutions composed of 38.4–75.0 wt% sulfuric acid in water with additional dissolved organic material have been measured over the temperature range 214.4–238.5 K using a Knudsen cell reactor. The solubility of acetaldehyde in H2SO4/H2O is enhanced by an order of magnitude by the presence of ethanol or acetone. The reactive uptake of acetaldehyde is enhanced by the presence of formaldehyde in acid solution. No significant formation of acetals from ethanol with carbonyl partners was observed. The solubility of acetone is unaffected by the presence of ethanol in solution and vice versa. Only polymerization of small aldehydes offers a potentially significant route to the accretion of organic material into acidic particles in the upper troposphere. The acid-catalyzed polymerization of aldehydes, RC(H)=O + R′C(H)=O, proceeds through the hydrated forms of the aldehydes, is optimized at acidities around 40 wt% H2SO4, and can potentially accumulate significant amounts (>20%) of organic material by mass in upper tropospheric particles.
Keywords: Organic; Aerosol; Atmosphere; Acid-catalyzed; Carbonyl; Liquid-phase reaction;

Aerosol load study in urban area by Lidar and numerical model by A. Miffre; M. Abou Chacra; S. Geffroy; P. Rairoux; L. Soulhac; R.J. Perkins; E. Frejafon (1152-1161).
Vertical profiles of particle mass concentration in the urban canopy above the city of Lyon have been obtained from Lidar measurements of atmospheric backscattering, over a period of three days. The concentrations measured at 50 m above the ground have been compared with the mass concentration of PM10 measured by a ground-based sampler located near the Lidar site. At certain times during the measurement campaign, the Lidar concentration measurements at 50 m agree reasonably well with the concentrations at ground level but at other times the differences between the two sets of measurements are so great that they cannot be explained by possible uncertainties in the data processing. Even when the Lidar and ground-based measurements coincide, there are significant differences between the two signals. To explain these differences we have computed the trajectories of the air parcels that pass over the Lidar, using a numerical model for the wind field that takes into account surface features such as relief and changes in roughness. This analysis showed that the differences can be explained by the meteorological conditions (wind speed and direction, vertical profiles of temperature) and the positions of the different sources of particulate matter relative to the measurement site. The combination of Lidar, ground-based sampler and air mass trajectory calculations is shown to be a powerful tool for discriminating between different sources of pollution, which could be useful in enforcing an urban air quality policy.
Keywords: Urban aerosol; UBL; PM10; Lidar; Numerical model;

Intra-urban correlation and spatial variability of air toxics across an international airshed in Detroit, Michigan (USA) and Windsor, Ontario (Canada) by Lindsay Miller; Lawrence D. Lemke; Xiaohong Xu; Shannon M. Molaroni; Hongyu You; Amanda J. Wheeler; Jason Booza; Alice Grgicak-Mannion; Richard Krajenta; Phillip Graniero; Helene Krouse; Lois Lamerato; Delbert Raymond; John Reiners; Linda Weglicki (1162-1174).
As part of a larger research project initiated by the Geospatial Determinants of Health Outcomes Consortium (GeoDHOC), an air quality study was conducted in an international airshed encompassing Detroit, Michigan, USA, and Windsor, Ontario, Canada. Active and passive samplers were used to measure nitrogen dioxide (NO2), sulfur dioxide (SO2), 26 volatile organic compounds (VOCs), 23 polycyclic aromatic hydrocarbons (PAHs) and pesticides, and three size fractions of particulate matter (PM) over a two-week period in September, 2008. Measurements of NO2 and 14 VOCs were found to be acceptable at 98 out of 100 passive monitoring sites. PAH and PM measurements were acceptable at 38 out of 50 active sites.Mean concentrations for all analytes except for PM2.5–10 were higher in Detroit than Windsor by a factor of up to 1.8. Strong statistical correlations were found among benzene, toluene, ethylbenzene, and xylene (BTEX), as well as between NO2 and PM in Detroit. In Windsor, the strongest correlations were between NO2 and total VOCs, as well as total PAHs and total VOCs. Differences in the degree of correlation observed in Detroit and Windsor are attributable to differences in the volume and composition of emissions within the two cities. Spatial variability was evaluated using a combination of statistical (coefficient of variation) and geostatistical (standardized variogram slope) metrics together with concentration maps. Greater spatial variability was observed for total VOCs and total BTEX in Detroit, while greater variability of NO2, total PAHs, and PM was found in Windsor. Results of this study suggest that statistical correlations between NO2 and other contaminants may not provide sufficient justification for the indiscriminant use of NO2 as a proxy for those contaminants if smaller scale features are to be reproduced.
Keywords: Air quality; International airshed; Spatial variability; Multi-pollutant; Correlation;

Anthropogenic magnetic particles and heavy metals in the road dust: Magnetic identification and its implications by Tao Yang; Qingsheng Liu; Haixia Li; Qingli Zeng; Lungsang Chan (1175-1185).
Magnetic properties of road dusts in the East Lake area in Wuhan, China, were measured and compared with the results of heavy metal analyses in order to delineate the sources of pollutants. A total of ninety-seven dust samples were collected spatially from four segments with different traffic density and field settings from the roads encircling the lake. Thermomagnetic and hysteresis measurements revealed that the dominant magnetic carrier is coarse-grained magnetite. Correlations between magnetic parameters and element concentrations with traffic density and distances to the industrial region revealed that elements Cu, Ni and Fe mainly originate from vehicle traffic, which is also the major source of coarser magnetic particles (e.g., pseudo-single-domain/multi-domain (PSD/MD) grains), while element Pb and the smaller grains such as single-domain (SD) magnetic particles mainly originate from industrial emissions. The ratio between anhysteretic remanent magnetization and low-field magnetic susceptibility (ARM/χ lf) can be employed as an indirect indicator for Cu, Fe and Ni emissions resulting from vehicle traffic. Due to the intermixture of elements from different sources, the element concentrations are not conclusive about the pollution source. A linear correlation between magnetic concentration-related parameters (e.g., ARM and saturation isothermal remanent magnetization, SIRM) and the concentrations of major elements (e.g., Cu, Co, Fe, Mn, Ni and V) suggests that they can be used as a proxy for heavy metal pollution. Road dusts in four segments show different magnetic characteristics, indicating various influxes of anthropogenic magnetic materials from vehicle traffic and industrial plants due to the different traffic loads and field settings. These results suggest that magnetic measurements can serve as an efficient complementary tool for the routinely employed geochemical methods to map the heavy metal pollution and trace the sources of pollutants in the road dust.
Keywords: Environmental magnetism; Heavy metals; Atmospheric particulate matter; Road dust;

Although NF3, a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere, little photochemical data exists from which to calculate its atmospheric removal rate. In this study, photodissociation quantum yields, Φ 1, were derived following 193.3 nm laser photolysis of NF3, and quantitative conversion of the F-atom photoproducts to OH, which was detected by laser induced fluorescence. Values of Φ 1(P, T) = (1.03 ± 0.05) were determined at pressures between 28 and 100 mBar of He or N2 and at either room temperature or 255 K. Absorption cross-sections, σ, obtained between 184 and 226 nm were combined with the values of Φ 1(P, T) to confirm a long (≈700 year) photolysis lifetime for NF3. No evidence for reaction of OH with NF3 was found, indicating that this process makes little or no contribution to NF3 removal from the atmosphere. These results underpin recent calculations of an NF3 atmospheric lifetime τ ≈ 550 years, largely controlled by photolysis in the stratosphere. In the course of this work the rate coefficient k 2(298 K) = (1.3 ± 0.2) × 10−11 cm3 molecule−1 s−1 was obtained for the reaction F + H2O.
Keywords: Photolysis; Cross-sections; Quantum yields; Greenhouse gas; NF3;

The increased use of ethanol in transportation fuels warrants an investigation of its consequences. An important component of such an investigation is the temperature dependence of ethanol and gasoline exhaust chemistry. We use the Master Chemical Mechanism (MCM, version 3.1, LEEDS University) with the SMVGEAR II chemical ordinary differential solver to provide the speed necessary to simulate complex chemistry to examine such effects. The MCM has over 13,500 organic reactions and 4600 species. SMVGEAR II is a sparse-matrix Gear solver that reduces the computation time significantly while maintaining any specified accuracy. Although we use a box model for this study, we determine and demonstrate in a separate study that the speed of the MCM with SMVGEAR II allows the MCM to be modeled in 3-dimensions. We also verified the accuracy of the model in comparison with smog chamber data. We then use the model with species-resolved tailpipe emissions data for E85 (15% gasoline, 85% ethanol fuel blend) and gasoline vehicles to compare the impact of each on nitrogen oxides, organic gases, and ozone as a function of ambient temperature and background concentrations, using Los Angeles in 2020 as a base case. We use two different emissions sets – one is a compilation of exhaust and evaporative data taken near 24 °C and the other from exhaust data taken at −7 °C – to determine how atmospheric chemistry and emissions are affected by temperature. We include diurnal effects by examining two day scenarios. We find that, accounting for chemistry and dilution alone, the average ozone concentrations through the range of temperatures tested are higher with E85 than with gasoline by ∼7 part per billion volume (ppbv) at higher temperatures (summer conditions) to ∼39 ppbv at low temperatures and low sunlight (winter conditions) for an area with a high nitrogen oxide (NOx) to non-methane organic gas (NMOG) ratio. The results suggest that E85's effect on health through ozone formation becomes increasingly more significant relative to gasoline at colder temperatures due to the change in exhaust emission composition at lower temperatures. Acetaldehyde and formaldehyde concentrations are also much higher with E85 at cold temperatures, which is a concern because both are considered to be carcinogens. These could have implications for wintertime use of E85. Peroxy acetyl nitrate (PAN), another air pollutant of concern, increases with E85 by 0.3–8 ppbv. The sensitivity of the results to box size, initial background concentrations, background emissions, and water vapor were also examined.
Keywords: Ethanol; Air pollution; Biofuels; Ozone;

Annual and seasonal variabilities in source contribution to total suspended particles (TSP) measured over an urban location in western India, Ahmedabad between May 2000 and January 2003 are examined in this study. Positive matrix factorization (PMF) resolved six factors including airborne regional dust, calcium carbonate rich dust, biomass burning/vehicular emissions, secondary nitrate/sulfate, marine aerosol, and smelter. In this study, non-parametric statistical tests including the Kruskal–Wallis analysis of variance (K–W ANOVA) and Spearman rank correlation (ρ) test were used to assess the annual and seasonal variations in factor contributions, and the influence of meteorology on these contributions, respectively. None of the factor contributions exhibited annual variations except airborne regional dust, and biomass burning/vehicular emissions factors. All of the factors exhibited seasonal variations. Several factor monsoon (July–September) median concentrations were significantly different from one or more of the other season medians. In general, it appeared that meteorological factors played a role in establishing the seasonal behavior of factor contributions. Factor contributions exhibited low to moderate correlations with meteorological parameters such as temperature, relative humidity, wind direction, and wind speed. Amongst all of the relationships, marine aerosol factor was reasonably well correlated with relative humidity (ρ = 0.73) and wind direction (ρ = 0.73) during the pre-monsoon season (March–May). This observation suggests that the aerosol transported by moisture laden winds from the Arabian sea contribute to this factor. The airborne regional dust factor was also moderately correlated with wind speed (ρ = 0.70) during the post-monsoon season. This relationship indicates that high regional dust concentrations are favored by high wind speeds and the resultant increase in dispersion.
Keywords: Total suspended particles (TSP); Source contribution; Annual and seasonal variations; Meteorology; Ahmedabad (India);

Characterization of organic coatings on hygroscopic salt particles and their atmospheric impacts by Alla Zelenyuk; Michael J. Ezell; Véronique Perraud; Stanley N. Johnson; Emily A. Bruns; Yong Yu; Dan Imre; M. Liz Alexander; Barbara J. Finlayson-Pitts (1209-1218).
The photooxidation of α-pinene in the presence of NO2, with and without added NaNO3 seed particles, has been studied in a large-diameter flow tube. Particles formed by homogeneous nucleation and by condensation on the pre-existing seeds were sampled at various stages of the reaction, dried using four diffusion dryers, size selected at different mobility diameters (d m) using a differential mobility analyzer (DMA), and characterized with a single particle mass spectrometer (SPLAT II). It was found that homogeneously nucleated particles are spherical, have a density (ρ) of 1.25 ± 0.02 g cm−3 (±2σ) and contain a significant amount of organic nitrates. The mass spectra of the low volatility products condensed on the NaNO3 seed particles were found to be virtually the same as in the case of homogeneous nucleation. The data show that the presence of even a submonolayer of organics on the NaNO3 particles causes water retention that leads to a decrease in particle density and that the amount of water retained increases with organic coating thickness. Thicker coatings appear to inhibit water evaporation from the particle seeds altogether. This suggests that in the atmosphere, where low volatility organics are plentiful, some hygroscopic salts will retain water and have different densities and refractive indices than expected in the absence of the organic coating. This water retention combined with the organic shell on the particles can potentially impact light scattering by these particles and activity as cloud condensation nuclei (CCN), as well as heterogeneous chemistry and photochemistry on the particles.
Keywords: Secondary organic aerosols; Single particle mass spectrometry; Density;

Signs of a negative trend in the MODIS aerosol optical depth over the Southern Balkans by M.E. Koukouli; S. Kazadzis; V. Amiridis; C. Ichoku; D.S. Balis; A.F. Bais (1219-1228).
A negative trend is being revealed in the MODIS aerosol optical depth [AOD] observed over the Southern Balkan/Eastern Mediterranean region. Collection 005 MODIS/Terra and MODIS/Aqua AOD at 470 nm measurements were evaluated against Brewer ground-based measurements over Thessaloniki, Greece and CIMEL ground-based measurements of AOD over Heraklion, Crete. A detailed study of the monthly, seasonal and inter-annual variability of the MODIS/Terra and MODIS/Aqua AOD values over selected locations around the Balkan Peninsula showed that the higher mean AOD values occurred in the spring and summer months, whereas the lowest were found in the winter-time. For all seasons, the highest AODs were observed for the northern-most latitudes with a marked decrease towards the southern-most sites. A statistically significant decreasing trend in aerosol load in the region over all sites as derived from the MODIS/Terra measurements gave the highest per annum change seen for the summer months to be −4.09 ± 2.34%, and the lowest for the winter months as −2.55 ± 4.36%, which also shows the higher variability.
Keywords: Urban aerosol; Aerosol optical depth; MODIS; Brewer spectrophotometer; CIMEL;

A methodology is presented to estimate the emissions of ships at berth based on their actual fuel consumption and the fuel quality. Accurate estimates of emissions from ships at berth demand reliable knowledge of the fuel consumption while at berth and associated fuel characteristics. However, assured information about energy use and fuel consumption of seagoing ships at berth is scarce. Proper estimation of ship emissions at berth is crucial for understanding the impact of shipping emissions on air quality and health in harbour cities as well as for a proper evaluation of the impact of abatement measures such as shore-side electricity and/or restrictions of sulphur content for shipping fuels to be used in ports. Therefore, a survey of energy consumption and fuel use on board of 89 seagoing ships was made in close cooperation with the Port of Rotterdam. Rotterdam is the major port of Europe ensuring that the results will have relevance for the larger European domain. On board of the ships at berth, a questionnaire was filled in by the chief engineer of that particular ship, assisted by two former mechanical shipping engineers employed at our organization. Survey results as well as the emission estimations are compared to the (scarce) information that is available and expert judgements in recent studies. The compiled survey data underlie the current Dutch emission estimation methodology for emissions of ships at berth.
Keywords: Fuel consumption; Harbours; Seagoing ships; Berth; Emissions; Fuel quality;

Coupling between meteorological factors and ambient aerosol load by Ankit Tandon; Sudesh Yadav; Arun K. Attri (1237-1243).
The coarser (CPM) and respirable (RPM) fractions of aerosol loads collected in a time sequence, during the onset of winter season in Delhi region, were subjected to Principal Component Analysis (15 elemental variables, 39 samples); the absolute mass contributed by each identified source to the CPM and RPM was quantified by using Absolute Principal Component Score (APCS) and Positive Matrix Factorization (PMF) method. Interestingly, the mass contributed by the local crustal source (material) to both fractions manifested undulating periodic behavior, a dominating harmonic corresponding to 24-h period was detected by using Discrete Fourier Transform (DFT). The corresponding harmonics, of varying strengths, were also detected in the recorded meteorological factors: Planetary Boundary Layer (PBL), Surface Level Temperature (T), Surface Level Relative Humidity (RH) and Wind Speed (WS). The analysis of the respective harmonic strength within the CPM, RPM, and meteorological factors suggested that the undulation observed in both size fractions of aerosol load from the local crust was affected by the meteorological factors. The large proportion of undulating loads (CPM and RPM), explained by the dominating harmonic, was fully accounted for by the empirical relation involving the discrete coupling parameters, and the recorded meteorological factors: PBL, T, RH and WS. The analysis suggests that the magnitude and the direction (‘positive’ load increase and ‘negative’ the reverse) of coupled meteorological factors'(s) effect on ambient CPM, RPM load is determined by the phase difference between the harmonic explaining the aerosol fraction's load and the corresponding harmonic present in the respective meteorological factor. The absolute mass contributions arising from the identified sources (APCS and PMF) allowed us to calculate the baseline ambient concentrations of undulating CPM and RPM loads, in the region of this study, affected by meteorological factors only.
Keywords: Aerosols; Meteorology; APCS; PMF; DFT; Coupling;