Atmospheric Environment (v.43, #28)

The Detroit Exposure and Aerosol Research Study (DEARS) provided data to compare outdoor residential coarse particulate matter (PM10–2.5) concentrations in six different areas of Detroit with data from a central monitoring site. Daily and seasonal influences on the spatial distribution of PM10–2.5 during Summer 2006 and Winter 2007 were investigated using data collected with the newly developed coarse particle exposure monitor (CPEM). These data allowed the representativeness of the community monitoring site to be assessed for the greater Detroit metro area. Multiple CPEMs collocated with a dichotomous sampler determined the precision and accuracy of the CPEM PM10–2.5 and PM2.5 data.CPEM PM2.5 concentrations agreed well with the dichotomous sampler data. The slope was 0.97 and the R 2 was 0.91. CPEM concentrations had an average 23% negative bias and R 2 of 0.81. The directional nature of the CPEM sampling efficiency due to bluff body effects probably caused the negative CPEM concentration bias.PM10–2.5 was observed to vary spatially and temporally across Detroit, reflecting the seasonal impact of local sources. Summer PM10–2.5 was 5 μg m−3 higher in the two industrial areas near downtown than the average concentrations in other areas of Detroit. An area impacted by vehicular traffic had concentrations 8 μg m−3 higher than the average concentrations in other parts of Detroit in the winter due to the suspected suspension of road salt. PM10–2.5 Pearson Correlation Coefficients between monitoring locations varied from 0.03 to 0.76. All summer PM10–2.5 correlations were greater than 0.28 and statistically significant (p-value < 0.05). Winter PM10–2.5 correlations greater than 0.33 were statistically significant (p-value < 0.05). The PM10–2.5 correlations found to be insignificant were associated with the area impacted by mobile sources during the winter. The suspected suspension of road salt from the Southfield Freeway, combined with a very stable atmosphere, caused concentrations to be greater in this area compared to other areas of Detroit. These findings indicated that PM10–2.5, although correlated in some instances, varies sufficiently across a complex urban airshed that that a central monitoring site may not adequately represent the population's exposure to PM10–2.5.
Keywords: Coarse particulate matter; Spatial; Temporal; Sampler;

In order to discuss the dry deposition fluxes of atmospheric fixed nitrogen species, observations of aerosol chemistry including nitrate (NO3 ) and ammonium (NH4 +) were conducted at two islands, Rishiri Island and Sado Island, over the Sea of Japan. Although the atmospheric concentrations of particulate NH4 +–N showed higher values than those of particulate NO3 –N at both sites, the dry deposition fluxes of the particulate NO3 –N were estimated to be higher than those of the particulate NH4 +–N. This was caused by the difference of particle sizes between the particulate NO3 and NH4 +; NH4 + was almost totally contained in fine particles (d < 2.5 μm) with smaller deposition velocity, whereas NO3 was mainly contained in coarse particles (d > 2.5 μm) with greater deposition velocity. Fine mode NO3 was strongly associated with fine mode sea-salt and mineral particles, of which higher concentrations shifted the size of particulate NO3 toward the fine mode range. This size shift would decrease the dry deposition flux of the fixed nitrogen species on coastal waters and accelerate atmospheric transport of them to the remote oceanic areas.
Keywords: Atmospheric input; Dry deposition flux; Fixed nitrogen species; Nitrate; Ammonium;

African dust contributions to mean ambient PM10 mass-levels across the Mediterranean Basin by X. Querol; J. Pey; M. Pandolfi; A. Alastuey; M. Cusack; N. Pérez; T. Moreno; M. Viana; N. Mihalopoulos; G. Kallos; S. Kleanthous (4266-4277).
Data on mass-levels of PM10 measured at regional background sites across the Mediterranean Basin, available from Airbase (European Environmental Agency) and from a few aerosol research sites, are compiled. PM10 levels increase from north to south and west to east of the Basin. These variations are roughly coincident with the PM10 African mineral dust load. However, when subtracting the African dust from mean PM10 levels using a consistent methodology, the PM10 background levels are still 5–10 μg m−3 higher in the Eastern Basin (EMB) when compared with those in the Western (WMB), mainly due to the higher anthropogenic and sea spray loads.As regards for the seasonal trends, these are largely driven by the occurrence of African dust events, resulting in a spring-early summer maximum over the EMB, and a clear summer maximum in the WMB, although in this later region the recirculations of aged air masses play an important role. Furthermore, a marked seasonal trend is still evident when subtracting the African dust load. This is characterised by a high summer maximum (driven by low precipitation, high insolation) and a winter minimum (intense synoptic winds).Important inter-annual variations in the dust contribution are detected, more evident in the southern sites. These differences are generally associated with the occurrence of extreme dust events. Generally, the years with higher dust contributions over the EMB correspond with lower contributions over the WMB, and vice versa.The characterization of individual particles, collected in both basins during African dust events, by scanning electron microscopy reveals only slight differences between them. This fact probably reflects the high degree of mixture of mineral dust from different sources before the transport towards the receptor sites.
Keywords: Dust; Air quality; Aerosols and climate; PM10 mass concentration;

The contribution of biological particles to observed particulate organic carbon at a remote high altitude site by Christine Wiedinmyer; Robert M. Bowers; Noah Fierer; Eszter Horanyi; Michael Hannigan; A. Gannet Hallar; Ian McCubbin; Kelly Baustian (4278-4282).
Although a significant fraction of atmospheric particulate mass is organic carbon, the sources of particulate organic carbon (POC) are not always apparent. One potential source of atmospheric POC is biological particles, such as bacteria, pollen, and fungal spores. Measurements of POC and biological particles, including bacteria, fungal spores, and pollen, were made as part of the Storm Peak Aerosol and Cloud Characterization Study in Steamboat Springs, CO in March–April 2008. Biological particles were identified and characterized using several methods. The results suggest that biological particles could account for an average of 40% of the organic carbon mass in particles with aerodynamic diameters less than 10 μm. These estimates of POC mass from biological particles are highly uncertain; however, the results suggest that biological particles could be a significant source of organic aerosol in the background continental atmosphere and further observations are needed to better constrain these estimates.
Keywords: Primary biological particles; Particulate organic carbon; High altitude site; Storm peak laboratory; Bacteria; Fungal spores;

Modeling PAH uptake by vegetation from the air using field measurements by Annick D. St-Amand; Paul M. Mayer; Jules M. Blais (4283-4288).
We examined PAH uptake by Norway spruce needles following the emergence of new buds in spring 2004–June 2005. Atmospheric PAH concentrations (gaseous phase and particle-bound) were monitored during this period, and PAH concentrations from these three environmental media were then used to calculate deposition and transfer velocities. Benzo(a)pyrene was found almost exclusively associated to particles and thus was used to determine a particle-bound deposition velocity of 10.8 m h−1. PAHs present in both compartments had net gaseous transfer velocities ranging from negligible values to 75.6 m h−1 and correlated significantly with log K OA. The loss velocities thereafter calculated were found to be higher for more volatile PAHs. Using the calculated average atmospheric PAH concentrations and deposition velocities, it was thus possible to model PAH uptake by vegetation through time. We demonstrate that this approach can be used to determine deposition velocities without the use of a surrogate surface. In considering both particulate-bound and gaseous deposition processes this model can be used not only to study air–foliage exchange of semi-volatile organic compounds, but also to illustrate the relative contribution of gaseous deposition and particulate-bound deposition in the overall atmospheric vegetation uptake of semi-volatile organic compounds.
Keywords: Polycyclic aromatic hydrocarbons; Modeling; Vegetation; Air; Contaminants;

Measurement and modeling of O3 variability in Shanghai, China: Application of the WRF-Chem model by Xuexi Tie; Fuhai Geng; Li Peng; Wei Gao; Chunsheng Zhao (4289-4302).
Since 2005, Shanghai Meteorological Bureau (SMB) has established an observational network for measuring VOC, NO x , O3 and aerosols in the Shanghai region. In this study, a rapid O3 changes from Aug/02/2007 to Aug/11/2007 was observed in the region. During this 10 day period, the noontime O3 maximum decreased from 100 to 130 ppbv to about 20–30 ppbv. In order to analyze the processes in controlling this rapid change of O3 during this short period, a newly developed regional chemical/dynamical model (WRF-Chem) is applied to study O3 variability in the Shanghai region. The model performances are evaluated by comparing the model calculation to the measurement. The result shows that the calculated magnitudes and diurnal variations of O3 are close to the measured results in city sites, but are underestimated at a rural petroleum industrial site, suggesting that the emissions from petroleum factories around this rural site are significantly underestimated and need to be improved. The calculated rapid changes of O3 concentrations, O3 precursors, and aerosols are consistent with the measured results, suggesting that the model is suitable to study the causes of this rapid O3 change. The model analysis indicates that weather conditions play important roles in controlling the surface O3 in the Shanghai region. During summer, there is a persistent sub-tropical high pressure system (SUBH) in southeast of Shanghai over Pacific Ocean. During the earlier time of the period (Aug/02–Aug/05), the SUBH system was weak, resulting in weak surface winds. With the calm winds, a noticeable noontime sea-breeze produced an inflow from ocean to land, generating a cycling pattern of wind directions. As a result, the high O3 concentrations were trapped in the Shanghai region, with a maximum concentration of 100–130 ppbv. By contrast, during the later time of the period (Aug/06–Aug/11), the SUBH was enhanced, resulting in strong surface winds. The high O3 concentrations formed in the city were rapidly transported to the downwind region of the city, resulting in low O3 concentrations in the Shanghai region. This study illustrates that the WRF-Chem model is a useful tool for studying the high variability of O3 concentrations in Shanghai, which has important implication for the prediction of high O3 concentration events in the city.
Keywords: WRF-Chem model; O3 in the Shanghai region;

Optimal temporal scale for the correlation of AOD and ground measurements of PM2.5 in a real-time air quality estimation system by Hui Li; Fazlay Faruque; Worth Williams; Mohammad Al-Hamdan; Jeffrey Luvall; William Crosson; Douglas Rickman; Ashutosh Limaye (4303-4310).
Aerosol optical depth (AOD), an indirect estimate of particulate matter using satellite observations, has shown great promise in improving estimates of PM2.5 (particulate matter with aerodynamic diameter less than or equal to 2.5 μm) surface. Currently, few studies have been conducted to explore the optimal way to apply AOD data to improve the model accuracy of PM2.5 in a real-time air quality system. We believe that two major aspects may be worthy of consideration in that area: 1) an approach that integrates satellite measurements with ground measurements in the estimates of pollutants and 2) identification of an optimal temporal scale to calculate the correlation of AOD and ground measurements. This paper is focused on the second aspect, identifying the optimal temporal scale to correlate AOD with PM2.5. Five following different temporal scales were chosen to evaluate their impact on the model performance: 1) within the last 3 days, 2) within the last 10 days, 3) within the last 30 days, 4) within the last 90 days, and 5) the time period with the highest correlation in a year. The model performance is evaluated for its accuracy, bias, and errors based on the following selected statistics: the Mean Bias, the Normalized Mean Bias, the Root Mean Square Error, Normalized Mean Error, and the Index of Agreement. This research shows that the model with the temporal scale: within the last 30 days, displays the best model performance in a southern multi-state area centered in Mississippi using 2004 and 2005 data sets.
Keywords: Aerosol optical depth (AOD); PM2.5; Air quality; Temporal scale; Remote sensing; Real-time system;

Experimental analysis of particle concentration heterogeneity in a ventilated scale chamber by Hanhui Jin; Qingping Li; Lihua Chen; Jianren Fan; Lin Lu (4311-4318).
The mixing processes of the aerosol particles from an outdoor environment in a ventilated scale chamber were experimentally studied. The particles were classified into five groups by size: 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm and 5.0–10.0 μm. The developing process for the concentration of each particle group was measured in different kinds of flow fields.The results show that the flow field configuration can effectively influence the dispersion time rate of the particles at certain positions. The increase in particle diameter can decrease the dispersion time rate. When the gas flow velocity is high, the particle dispersion time rate is independent of particle size; but when the gas flow velocity is low, particle size can significantly affect the particle dispersion time rate because the turbulent diffusion becomes important in the air and particle transport. The uniformity of the particle concentration for certain positions in steady state tends to be controlled by the inflow velocity, flow field configuration and the particle diameters.
Keywords: Indoor; Fine particle; Mixing; Concentration heterogeneity; Flow field; Experimental studies;

Atmospheric DDTs over the North Pacific Ocean and the adjacent Arctic region: Spatial distribution, congener patterns and source implication by Xiang Ding; Xin-Ming Wang; Qiao-Yun Wang; Zhou-Qing Xie; Cai-Hong Xiang; Bi-Xian Mai; Li-Guang Sun (4319-4326).
During the 2003 Chinese Arctic Research Expedition (CHINARE 2003) from Bohai Sea to the high Arctic (37°N–80°N), air samples were collected and analyzed for DDTs. ∑DDTs (sum of six congeners) ranged from 0.52 to 265 pg m−3 with an average of 13.1 pg m−3. Higher DDT concentrations were observed in Bohai Sea and near eastern Russia. The congener patterns were obviously different between the Far East Asia and the higher latitudinal regions that p,p'-DDT and o,p'-DDT were dominated in the former; while o,p'-DDT and o,p'-DDE were dominated in the latter. The source contributions of technical DDT and dicofol type DDT were estimated. Results showed that technical DDT was the dominant source (>94%) which was fresher in the Far East Asia compared to the North Pacific Ocean and the Arctic. For dicofol type DDT, the estimated contribution was minor. The “new”o,p'-DDT observed should have relatively more contribution from dicofol type DDT in the North Pacific Ocean and the Arctic.
Keywords: DDTs; Far East Asia; North Pacific ocean; Arctic;

Evaluating inter-continental transport of fine aerosols: (1) Methodology, global aerosol distribution and optical depth by Junfeng Liu; Denise L. Mauzerall; Larry W. Horowitz; Paul Ginoux; Arlene M. Fiore (4327-4338).
Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997–2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region's emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57–95%) over all regions, but are responsible for a smaller fraction of AOD (26–76%). We define “background” aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36–97% for surface concentrations and 38–89% for AOD. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor's background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust aerosols and their precursors from an RPI will simultaneously improve both air quality and visibility over a receptor region.
Keywords: Inter-continental transport; Source-receptor relationships; Aerosols; Air quality; Optical depth;

Evaluating inter-continental transport of fine aerosols:(2) Global health impact by Junfeng Liu; Denise L. Mauzerall; Larry W. Horowitz (4339-4347).
In this second of two companion papers, we quantify for the first time the global impact on premature mortality of the inter-continental transport of fine aerosols (including sulfate, black carbon, organic carbon, and mineral dust) using the global modeling results of (Liu et al., 2009). Our objective is to estimate the number of premature mortalities in each of ten selected continental regions resulting from fine aerosols transported from foreign regions in approximately year 2000. Our simulated annual mean population-weighted (P-W) concentrations of total PM2.5 (aerosols with diameter less than 2.5 μm) are highest in East Asia (EA, 30 μg m−3) and lowest in Australia (3.6 μg m−3). Dust is the dominant component of PM2.5 transported between continents. We estimate global annual premature mortalities (for adults age 30 and up) due to inter-continental transport of PM2.5 to be nearly 380 thousand (K) in 2000. Approximately half of these deaths occur in the Indian subcontinent (IN), mostly due to aerosols transported from Africa and the Middle East (ME). Approximately 90K deaths globally are associated with exposure to foreign (i.e., originating outside a receptor region) non-dust PM2.5. More than half of the premature mortalities associated with foreign non-dust aerosols are due to aerosols originating from Europe (20K), ME (18K) and EA (15K); and nearly 60% of the 90K deaths occur in EA (21K), IN (19K) and Southeast Asia (16K). The lower and higher bounds of our estimated 95% confidence interval (considering uncertainties from the concentration–response relationship and simulated aerosol concentrations) are 18% and 240% of the estimated deaths, respectively, and could be larger if additional uncertainties were quantified. We find that in 2000 nearly 6.6K premature deaths in North America (NA) were associated with foreign PM2.5 exposure (5.5K from dust PM2.5). NA is least impacted by foreign PM2.5 compared to receptors on the Eurasian continent. However, the number of premature mortalities associated with foreign aerosols in NA (mostly occurring in the U.S.) is comparable to the reduction in premature mortalities expected to result from tightening the U.S. 8-h O3 standard from 0.08 ppmv to 0.075 ppmv. International efforts to reduce inter-continental transport of fine aerosol pollution would substantially benefit public health on the Eurasian continent and would also benefit public health in the United States.
Keywords: Inter-continental transport; PM2.5; Aerosols; Air pollution; Premature mortalities; Public health;

An interdisciplinary field study designed to investigate the spatial and temporal variability of atmospheric aerosols during high particulate matter (PM) events along the US–Mexico border near Yuma, AZ was run during the week of March 18, 2007. The experiments were designed to quantify chemical composition and physical phenomena governing the transport of aerosols generated from episodic high PM events. The field study included two micrometeorological monitoring sites; one rural and one urban, equipped with sonic anemometers, continuous particulate concentration monitors and ambient aerosol collection equipment. In addition to the two main monitoring sites, five additional locations were equipped with optical particle counters to allow for the investigation of the spatial and temporal distribution of PM 2.5 in the urban environment. In this paper, the meteorological and turbulence parameters governing the distribution and concentration of PM 2.5 in the urban environment for two high-wind erosion events and one burning event are compared. The interaction between local atmospheric conditions and the particulate distribution is investigated. Results indicate that a single point measurement in the urban area of Yuma may not be sufficient for determining the ambient PM concentrations that the local population experiences; all three high PM events indicated PM 2.5 varied considerably with maximum urban concentrations 5–10 times greater than the measured minima. A comparison of inorganic and carbonaceous content of the aerosols for the three high PM events is presented. The comparison shows an increase in silicon during crustal dust events and an increase in elemental and organic carbon during the burn event. Additional surface chemistry analysis, using time-of-flight secondary ion mass spectrometry (ToF-SIMS), for aerosols collected at the urban and rural sites during the burn event are discussed. The surface chemistry analysis provides positive ion mass spectra of organic and inorganic species in the ambient aerosol, and can be used to determine the type of combustion process that contributed to an increase in PM concentration during the burn event.
Keywords: US–Mexico border; PM 2.5; High-wind; Burning; ToF-SIMS;

Aerosols and associated precipitation patterns in Atlanta by Matthew C. Lacke; Thomas L. Mote; J. Marshall Shepherd (4359-4373).
The role of aerosol concentrations on summer precipitation was examined in Atlanta, Georgia for the period 2003–2004. Each day of the week was examined to ascertain their aerosol concentrations. Thursday had the highest median 2.5 μm particulate matter (PM 2.5) concentrations at two of three Environmental Protection Agency stations. Monday and Thursday had the largest area of significantly different precipitation when compared to other days of the week. All but the southeast quadrant of the metropolitan area had a significant difference in precipitation on high versus low aerosol days. High aerosol days had greater instability (higher average convective available potential energy and lower convective inhibition), and a slightly more shallow mixing layer when compared to low aerosol days. Most of metropolitan Atlanta had higher precipitation amounts on high aerosol days and was significantly different from low aerosol days.
Keywords: Aerosols; Particulate matter; Precipitation; Atlanta;