Average Dry Deposition Velocity Research Articles

Dry deposition of particulate matter and its associated soluble ions on five broadleaved species in Taichung, central Taiwan

Many studies have estimated particulate matter (PM) removal by urban trees using dry deposition models; however, few studies have quantified the accuracy of their results. Thus, this study investigated the dry deposition of PM and its associated soluble ions in five broadleaved species in three districts of Taichung, central Taiwan, through field experiments. The total suspended particulate (TSP) dry deposition flux on leaf surfaces varied with sampling time, site, and tree species. By contrast, single-factor effects were observed for PM10 and PM2.5. The average dry deposition velocities of TSPs, PM10, and PM2.5 were 0.63, 0.062, and 0.028 cm s−1, respectively. Moreover, the dry deposition velocities of sulfate and nitrate were estimated to be 0.186 and 0.194 cm s−1, respectively. A significant relationship was observed between the ambient concentration and the dry deposition flux for all size fractions of PM. By contrast, weak and negative correlations were found between particle deposition velocity and wind speed. The measured PM2.5 dry deposition velocity was approximately equal to the dry deposition velocity obtained with the i-Tree model (0.03 cm s−1), which indicated the promising application potential of i-Tree in Taiwan. Compound and rough leaves, such as leaves of the Taiwan golden-rain tree, intercepted a high amount of PM2.5, whereas the pongam tree, which has thin leaves and wax surfaces, exhibited the lowest TSP interception. Species difference mostly occurred in the dry deposition flux of nitrate rather than sulfate; however, the interception of sulfate by trees revealed the possibility of the long-range transport of air pollutants. The results of this study elucidate the dry deposition of PM and its associated soluble ions in real-world situations.

Atmospheric Deposition of Organochlorine Pesticides (OCPs): Species, Levels, Diurnal and Seasonal Fluctuations, Transfer Velocities.

Organochlorine pesticides (OCPs) in the persistent organic pollutants class are pollutants that can enter water reservoirs, soils, and sediments by atmospheric deposition. The aim of the present study was to determine the total atmospheric deposition fluxes of OCPs in a semi-rural area in Bursa, Turkey. Total deposition fluxes, phase distributions, dry deposition velocities and mass transfer coefficients were calculated in the samples collected during day and night periods. Ambient air OCP samples were also taken simultaneously. Samples were analyzed for 9 OCP compounds (alpha-, beta-, and gamma-hexachlorocyclohexane; heptachlor epoxide; endrin; endosulfan beta; endrin aldehyde; and methoxychlor). OCPs were found predominantly in gas and dissolved phases in all seasons for the ambient air and deposition samples, respectively. The annual maximum averages of deposition fluxes for dissolved and particulate phases for the beta-HCH compound were 200.2ng/m2-day and 28.6ng/m2-day, respectively. The average dry deposition velocity and mass transfer coefficient values calculated for OCPs were 4.6 ± 5.5cm/s and 0.46 ± 0.37cm/s, respectively, and these values were in line with the values in the literature. In the nighttime and daytime samples, the average deposition fluxes of OCP compounds in the dissolved phase were 1.5-10 times higher than those in the particulate phase. Although there were no great differences in daytime and nighttime samples, it was found that the flux values during daytime periods were sometimes higher.

Wetlands with greater degree of urbanization improve PM2.5 removal efficiency

In recent decades, China has experienced both rapid urbanization and heavy air pollution and the rapid urbanization trend would be continue in the next decade. Wetlands have been shown to be efficient in particle removal, primarily through dry deposition and leaf accumulation. Thus, a more comprehensive understanding of PM2.5 removal by wetlands during urbanization processes could inform urban planning. In the current study, three wetland plots, Cuihu Lake Park (CL), Summer Palace (SP), and Olympic Park (OP), were selected as low, medium, and highly degrees of urbanization site respectively based on the proportions of building and traffic district areas to compare the removal efficiencies. Results show the average dry deposition velocity in OP was significantly higher than CL and SP. Dry deposition is mainly influenced by meteorological conditions. Buildings and other infrastructure make the meteorological conditions conducive to deposition, resulting in higher wind velocity, higher temperature, and more intense turbulence between buildings. Variation in leaf accumulation was not statistically significant between the three plots, and plant species was the major factor affecting the amount of accumulation. The dry deposition contribution to particle removal increases with degree of urbanization. The average dry deposition accounted for 39.74%, 52.55%, and 62.75% at low, middle and high level respectively. Therefore, Wetlands with greater degree of urbanization improve PM2.5 removal efficiency primarily by accelerating the dry deposition process. The result emphasizes the importance of wetlands in particle removal in highly urbanized areas and thus more wetlands should be preserved and/or created during urban expansion.

Concentration, size distribution and dry deposition of amines in atmospheric particles of urban Guangzhou, China

Size-segregated PM10 samples were collected in Guangzhou, China during autumn of 2014. Nine amines, including seven aliphatic amines and two heterocyclic amines, were detected using a gas chromatography-mass spectrometer after derivatization by benzenesulfonyl chloride. The total concentration of the nine amines (Ʃamines) was 79.6–140.9 ng m−3 in PM10. The most abundant species was methylamine (MA), which had a concentration of 29.2–70.1 ng m−3. MA, dimethylamine (DMA), diethylamine (DEA) and dibutylamine (DBA) were the predominant amines in the samples and accounted for approximately 80% of Ʃamines in each size segment. Two heterocyclic amines, pyrrolidine (PYR) and morpholine (MOR), were detected in all samples and had average concentrations of 1.14 ± 0.37 and 1.89 ± 0.64 ng m−3, respectively, in particles with aerodynamic diameters < 3 μm. More than 80% of Ʃamines were found in particles with diameters <1.5 μm, indicating that amines are mainly enriched in fine particles. All amines exhibited a bimodal distribution with a fine mode at 0.49–1.5 μm and a coarse mode at 7.2–10 μm. The maximum contributions of amines to particles (0.21%) and amines-N to water-soluble organic nitrogen (WSON) (3.1%) were found at the sizes < 0.49 μm. The maximum contribution of amines-C to water-soluble organic carbon (WSOC) was 1.6% over the size range of 0.95–1.5 μm. The molar ratio of Ʃamines to ammonium ranged from 0.0068 to 0.0107 in particles with diameters <1.5 μm, and the maximum ratio occurred in the smallest particles (diameter< 0.49 μm). The average dry deposition flux and velocity of Ʃamines in PM10 were 7.9 ± 1.6 μg m−2 d−1 and 0.084 ± 0.0021 cm s−1, respectively. The results of this study provide essential information on the contribution of amines to secondary organic aerosols and dry removal mechanisms in urban areas.

Atmospheric Dry Deposition Fluxes and Sources of Polycyclic Aromatic Hydrocarbons in Lanzhou Valley, Northwest China

The atmospheric dry deposition flux pollution levels were determined and the sources apportioned for 15 US EPA priority polycyclic aromatic hydrocarbons (PAHs) collected at 13 sampling sites in the Lanzhou valley using passive sampling techniques. The results are as follows. The annual atmospheric dry deposition fluxes ranged from 7.48 to 53.94 μg·(m2·d)-1, with a mean of 18.65 μg·(m2·d)-1. The highest flux levels for both the heating and non-heating seasons, 60.85 μg·(m2·d)-1 and 47.03 μg·(m2·d)-1, respectively, appeared at the traffic site (Donggang Bridge), where the heaviest traffic in the Lanzhou valley occurs. The lowest flux levels of 8.16 μg·(m2·d)-1 and 6.80 μg·(m2·d)-1 for the heating and non-heating seasons, respectively, were found at Baita Mountain, which has a higher percentage of vegetation cover. Meanwhile, the flux levels at the background site (Guantangou Mountain) were significantly lower than those of the other sampling sites. For dry deposition, the PAH components Phe, Flua, Flu, and Pyr were dominant in the heating and non-heating periods, and the sums of the percentages of 3- and 4-ring PAHs were 87.53% for the heating season and 82.73% for the non-heating season. Moreover, the percentage of 5- and 6-ring PAHs for the non-heating period was higher than that for the heating period, which may be because the lighter PAHs were easily volatilized, and thus escaped. Furthermore, the sources of atmospheric dry deposition were identified by principal component analysis (PCA). The results of source apportionment showed that the main atmospheric PAH dry deposition in the Lanzhou valley were from vehicle exhaust emissions, coal combustion, and the coking industry. In further detail, coal combustion and the coking industry contributed most of the PAH dry deposition emissions during the heating period except for the traffic area site of Donggang Bridge, whereas vehicle exhaust was the dominant contributor during the non-heating season. In addition, the annual average dry deposition velocities of atmospheric PAHs were calculated using the dry deposition model for three sites: 0.20 cm·s-1 downtown (Environmental Protection Agency of Lanzhou; JCZ), 0.15 cm·s-1 in an industrial area (Lanyuan Hotel of Xigu; LLH), and 0.17 cm·s-1 in a traffic area (the Staff Hospital of Gansu Province; ZGH), of which the latter two were relatively lower because of comprehensive meteorological factors such as wind speed, temperature, and land use categories. Regarding the dry deposition flux values of the 3- and 4-ring PAHs, the simulated values were a bit larger than the observed values, but all were at the same level of magnitude. However, the simulated flux values were closer to their observed values for 4-ring PAHs than for 3-ring PAHs, which indicated that 3-ring PAHs were lost more easily than 4-ring PAHs were during monitoring.

Dry and wet deposition of polycyclic aromatic hydrocarbons and comparison with typical media in urban system of Shanghai, China

Polycyclic aromatic hydrocarbons (PAHs) were studied in dry and wet deposition samples collected at urban and suburban sites of Shanghai, China from April 2014 to April 2015. Average wet deposition fluxes of PAHs were higher than dry deposition (62.6 ± 41.5 vs. 26.9 ± 14.4 μg/m2/day). However, dry deposition removed more PAHs than wet deposition (69% vs. 31%) due to much shorter durations of wet deposition. The highest dry and wet deposition fluxes were in fall and winter, respectively. The highest amount of dry deposition was in fall and the highest of wet deposition was in summer. The contribution of wet deposition to total deposited PAHs in Shanghai, East China was higher than that in northern China and lower than that in southern China. The difference can be explained by both precipitation amount and removal efficiency (washout ratio). Average dry deposition velocity and washout ratio of particle-associated PAHs were 5.2 cm/s and 5.8 × 104, respectively. Four sources of deposited PAHs were unraveled by positive matrix factorization (PMF) model: traffic, coal combustion, coking and volatilization, contributing 28.7%, 24.6%, 23.7% and 23.0%, respectively. More contribution of traffic and less coal combustion and volatilization were found at urban than at suburban site. As the connection between aerosol and surface soil, deposition had a different PAH composition from those in the two sides, containing more low MW PAHs. That arose the concern that dry deposition velocity and particle washout ratio could be overestimated if coarse particulate matter was excluded from the calculation. Although deposition has been considered as the predominant pathway of PAHs to urban surface system, the PAH composition in street dust differed drastically from that in deposition. This indicated that other sources (e.g. traffic) in urban system could have a greater contribution to PAHs than it had been identified in deposition samples.

Atmospheric PM2.5 and Depositions of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Kaohsiung Area, Southern Taiwan

ABSTRACTKaohsiung County, in southern Taiwan, has both highly industrial and rural areas. In this study, the characteristics of PCDD/Fs in the ambient air of Kaohsiung (urban), Meinong (rural) and Xiaogang (heavy industrial zone) in 2014 and 2015 were modeled based on the prevailing meteorological conditions and the measured ambient air concentrations of PM2.5, PM10 and TSP. The yearly average PM2.5 concentrations in the ambient air of the three areas were in the range of 23 to 31 µg m–3, all above the National Air Quality Standard of Taiwan (15 µg m–3). The simulated average concentrations of PCDD/Fs in the whole of Kaohsiung area in terms of toxicity equivalent were in the range of 0.034–0.053 pg WHO2005-TEQ m–3. The average total deposition fluxes of total-PCDD/Fs-WHO2005-TEQ ranged between 155.4 and 276.6 pg WHO2005-TEQ m–2 month–1 with 1,2,3,7,8-PeCCD and 2,3,4,7,8-PeCDF being the dominant congeners in terms of PCDD/Fs WHO2005-TEQ. Xiaogang area with highly industrial activities had the highest concentrations of PM2.5 and PCDD/Fs and corresponding total-PCDD/Fs WHO2005-TEQ deposition fluxes, while the Meinong in the rural site recorded the lowest. Average dry deposition velocities of total PCDD/Fs WHO2005-TEQ for both 2014 and 2015 were 0.162, 0.148 and 0.161 cm s–1 for Kaohsiung, Meinong and Xiaogang, respectively, while the average scavenging ratios of total PCDD/Fs WHO2005-TEQ were 6232, 4701 and 6802, for Kaohsiung, Meinong and Xiaogang, respectively. The information provided in this work is useful for both further studies and environmental control strategies concerning atmospheric aerosols and dioxins.

Atmospheric Deposition of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans at Coastal and High Mountain Areas in Taiwan

Atmospheric deposition is of great importance for the sink of air pollutants to the environment, either from local sources as well as coming from long range transport. To further understand the combined impact of both long-range transport from South East Asia and local emission sources of pollutants, the characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the ambient air of two background sites in Taiwan namely, Hengchun (coastal area) and Lulin (high mountain area), were simulated by regression of PM_10 versus total-PCDD/F mass concentration, modeling of gas-particle partitioning, and simulations of both dry and wet deposition. The simulated PCDD/F concentrations at Hengchun, ranged between 0.0039-0.0106 and 0.0054-0.0138pg WHO2005-TEQ m^(-3) for 2012 and 2013, respectively. For Lulin site, the PCDD/F concentrations ranged between 0.0016-0.0029 and 0.0016-0.0032 pg WHO_2005-TEQ m^(-3) for 2012 and 2013, respectively. The WHO_2005-TEQ ratios of PCDDs to PCDFs at both sites were less than unity, indicating that PCDF dominated the total toxicity. The results show that higher chlorinated PCDD/Fs primarily present in particulate phase for all seasons at both sampling sites especially in winter. Average dry deposition fluxes at Hengchun (57.1 pg WHO2005-TEQ m^(-2) month^(-1)) were approximately 5.1 times higher than those at Lulin (11.2pg WHO2005-TEQ m^(-2) month^(-1)). The annual average dry deposition velocities were estimated to be 0.28 and 0.22cm/s for Henchun and Lulin, respectively. For the whole period (2012-2013), the mean monthly wet deposition fluxes at Hengchun (averaged 11.7pg WHO_2005-TEQm^(-2) month^(-1)) were 1.44 times higher than that at Lulin (averaged 8.11pg WHO2_005-TEQ m^(-2) month^(-1)). The calculated annual average total-PCDD/Fs-WHO_2005-TEQ concentrations in the rain were 0.064 and 0.027pg WHO_2005-TEQ L^(-1) for Henchun and Lulin, respectively. The estimated annual average scavenging ratios of total-PCDD/Fs-WHO_2005-TEQ were 8015 and 13450 for Henchun and Lulin, respectively. Similarly, for the entire study period (2012–2013), the average annual total (dry + wet) deposition flux of total PCDD/Fs-WHO_2005-TEQ in the terms of pg WHO_2005-TEQ m^(-2) year^(-1) at Hengchun (824.9) was 3.5 times higher than those in Lulin (232.0). On the basis of total PCDD/Fs-WHO_2005-TEQ, the mean fraction contributed by dry deposition at Hengchun were 78.2% and 78.9% in 2012 and 2013, respectively, while at Lulin the average fraction contributed by dry deposition at Lulin were 56.5% and 69.1% in 2012 and 2013, respectively. Higher chlorinated congeners OCDD, OCDF, 1, 2, 3, 4, 6, 7, 8-HpCDF and 1, 2, 3, 4, 6, 7, 8-HpCDD dominated in terms of mass fractions of total PCDD/F deposition fluxes for all seasons at both sites. However on the basis of total PCDD/Fs-WHO_2005-TEQ deposition fluxes, the most dominant congeners were 2, 3, 4, 7, 8-PeCDF, 1, 2, 3, 7, 8-PeCDD and 2, 3, 7, 8-TeCDD during the whole sampling period at both sites. The results of this study provide useful information for both environmental impact assessment and control strategies of persistent organic compounds (POPs).

Ambient Air Particulate and Particulate-Bound Hg (Hg[p]) Concentration: Dry Deposition Study Using a Cold Vapor Atomic Fluorescence Spectrometry (CVAFS) Analyzer in Westin Park, Taiwan

Ambient air particulate-bound Hg (Hg[p]) concentrations, dry deposition and dry deposition velocity were measured using a cold vapor atomic fluorescence spectrometry (CVAFS) analyzer in the spring season (between March 2011 to June 2011) at the Westin Park sampling site, in Sha-Lu central Taiwan. The results indicated that the highest ambient air Hg(p) concentrations total suspended particles (TSP) occurred in April (0.050 ng/m3) while the lowest ambient air Hg(p) concentrations in TSP occurred in March (0.011 ng/m3). Moreover, the results showed that the highest Hg(p) dry deposition occurred in June (0.019 ng/m2*min), while the lowest ambient air Hg(p) dry deposition occurred in March (0.002 ng/m2*min). In addition, the results also showed that the highest and lowest dry deposition velocity for ambient air Hg(p) occurred in June (2.46 cm/sec) and May (0.18 cm/sec), respectively. Finally, the average highest and lowest dry deposition velocity for ambient air particulates occurred in March (9.010 cm/sec) and April (2.09 cm/sec), respectively.

Dry deposition fluxes and deposition velocities of seven trace metal species at five sites in central Taiwan – a summary of surrogate surface measurements and a comparison with model estimations

Abstract. Daily air concentrations and dry deposition fluxes of seven metal species were monitored at five sites in central Taiwan for five or six days every month from September 2009 to August 2010. Annual average concentrations at the five sites were in the range of 2.8 to 3.6 ng m−3 for As, 25 to 82 ng m−3 for Mn, 1900 to 2800 ng m−3 for Fe, 69 to 109 ng m−3 for Zn, 18 to 33 ng m−3 for Cr, 60 to 110 ng m−3 for Cu, and 25 to 40 ng m−3 for Pb. Annual average dry deposition fluxes were on the order of 3, 20, 400, 50, 25, 50, and 50 μg m−2 day−1 for As, Mn, Fe, Zn, Cr, Cu, and Pb, respectively. Annual average dry deposition velocities (Vd) for the seven metal species ranged from 0.18 to 2.22 cm s−1 at these locations. Small seasonal and geographical variations, e.g. from a few percent to a factor of 2 for different species and/or at different locations, were found in the measured concentrations, fluxes, and Vds. The measured fluxes and air concentrations had moderate to good correlations for several of the species at several of the sites (e.g. Fe, Zn, and Mn at most of the sites), but had either weak or no correlations for the other species or at the other sites (e.g. As at Sites I and III, Zn and Cr at Site IV, and Cu at most of the sites). The latter cases were believed to have large uncertainties in the flux measurements using surrogate surfaces. Sensitivity tests were conducted for particle Vds using a size-segregated particle dry deposition model, assuming various combinations of three lognormal size distributions representing fine particles (PM2.5), coarse particles (PM2.5–10), and super-sized particles (PM10+), respectively. It was found that the measured dry deposition fluxes can be reproduced reasonably well using the size-segregated particle dry deposition model if the mass fractions of the metal species in PM2.5, PM2.5–10 and PM10+ were known. Significant correlations between the modeled and the measured daily fluxes were found for those cases that were believed to have small uncertainties in the flux measurements.

Dry deposition velocity of total suspended particles and meteorological influence in four locations in Guangzhou, China

AbstractDry deposition velocity of total suspended particles (TSP) is an effective parameter that describes the speed of atmospheric particulate matter deposit to the natural surface. It is also an important indicator to the capacity of atmosphere self-depuration. However, the spatial and temporal variations in dry deposition velocity of TSP at different urban landscapes and the relationship between dry deposition velocity and the meteorological parameters are subject to large uncertainties. We concurrently investigated this relationship at four different landscapes of Guangzhou, from October to December of 2009. The result of the average dry deposition velocity is (1.49 ± 0.77), (1.44 ± 0.77), (1.13 ± 0.53) and (1.82 ± 0.82) cm/sec for urban commercial landscape, urban forest landscape, urban residential landscape and country landscape, respectively. This spatial variation can be explained by the difference of both particle size composition of TSP and meteorological parameters of sampling sites. Dry deposition velocity of TSP has a positive correlation with wind speed, and a negative correlation with temperature and relative humidity. Wind speed is the strongest factor that affects the magnitude of TSP dry deposition velocity, and the temperature is another considerable strong meteorological factor. We also find out that the relative humidity brings less impact, especially during the dry season. It is thus implied that the current global warming and urban heat island effect may lead to correlative changes in TSP dry deposition velocity, especially in the urban areas.

Measuring and Modeling Atmospheric Arsenic Pollutants, Total As, As(III), and As(V), at Five Characteristic Sampling Sites

This investigation determines ambient air arsenic (As), As(III), and As(V) concentrations in total suspended particulates (TSP) and dry deposition. Calculated/measured dry deposition flux ratios of ambient air As, As(III) and As(V) were evaluated using two dry deposition models at five characteristic sampling sites during 2009-2010.The highest average concentrations of As, As(III) and As(V) in TSP and dry deposition were measured at the Quan-xing industrial sampling site during August-January. The Quan-xing site, with many industrial factories under process around there regions, its air is extremely polluted. In addition, the average dry deposition velocities for ambient air total arsenic (As) at Bei-shi, Chang-hua, He-mei, Quanxing and Gao-mei were 0.60 (cm/sec), 0.57 (cm/sec), 0.73 (cm/sec), 0.67 (cm/sec) and 0.66 (cm/sec), respectively at these five characteristic sampling sites. The highest average seasonal variation for As, As(III) and As(V) in TSP and dry deposition were in winter and fall due to emissions from fossil fuel combustion by the nearby Taichung Thermal Power Plant (TTPP) and for household heating. The Noll and Fang model can be applied to predict dry deposition of As, As(III), and As(V) at these sampling sites.

Atmospheric sulfur deposition and the sulfur nutrition of crops at an agricultural site in Jiangxi province of China

During the period From November 1998 to October 1999, the air sulfur dioxide (SO2) and sulfate (SO2−4) concentrations were measured and rain water was collected on farmland at Yingtan, a typical red soil area in the Jiangxi province of China. Based on hourly meteorological data and surface resistance data from the literature, the dry deposition velocities of SO2 and SO2−4 were computed using a three-layer resistance analogy model, and sulfur dry deposition was calculated. The wet deposition was obtained from precipitation amount and sulfur concentrations in rainwater. The average dry deposition velocities of SO2 and SO2−4 on farmland were found to be 0.38 ± 0.16 cm s−1 (monthly average 0.16–0.55 cm s−1) and 0.20 ± 0.12 cm s−1 (monthly average 0.15–0.27 cm s−1), respectively. The annual total sulfur deposition for the study region is about 103 kg S ha−1, of which 83% is dry deposition. The uncertainties due to measurement and the dry deposition model are less than 30%. It is also found that atmospheric deposition plays a key role in sulfur circulation within the agrecosystem, accounting for more than 90% of the total sulfur input to farmland

Sources, transport, and sinks of SO2 over the equatorial Pacific during the Pacific Atmospheric Sulfur Experiment

The Pacific Atmospheric Sulfur Experiment (PASE) is the first sulfur-budget field experiment to feature simultaneous flux measurements of DMS marine emissions and SO2 deposition to the ocean surface. We make use of these data to constrain a 1-D chemical transport model to study the production and loss pathways for DMS and SO2 over the equatorial Pacific. Model results suggest that OH is the main sink for DMS in the boundary layer (BL), and the average DMS-to-SO2 conversion efficiency is ~73%. In an exploratory run involving the addition of 1 pptv of BrO as a second oxidant, a 14% increase in the DMS flux is needed beyond that based on OH oxidation alone. This BrO addition also reduces the DMS-to-SO2 conversion efficiency from 73% to 60%. The possibility of non-DMS sources of marine sulfur influencing the estimated conversion efficiency was explored and found to be unconvincing. For BL conditions, SO2 losses consist of 48% dry deposition, while transport loss to the BuL and aerosol scavenging each account for another 19%. The conversion of SO2 to H2SO4 consumes the final 14%. In the BuL, cloud scavenging removes 85% of the SO2, thus resulting in a decreasing vertical profile for SO2. The average SO2 dry deposition velocity from direct measurements (i.e., 0.36 cm sec−1) is approximately 50% of what is calculated from the 1-D model and the global GEOS-Chem model. This suggests that the current generation of global models may be significantly overestimating SO2 deposition rates over some tropical marine areas. Although the specific mechanism cannot be determined, speculation here is that the dry deposition anomalous results may point to the presence of a micro-surface chemical phenomenon involving partial saturation with either S(IV) and/or S(VI) DMS oxidation products. This could also appear as a pH drop in the ocean’s surface microfilm layer in this region. Finally, we propose that the enhanced SO2 level observed in the lower free troposphere versus that in the upper BuL during PASE is most likely the result of transported DMS/SO2-rich free-tropospheric air parcels from the east of the PASE sampling area, rather than an inadequate representation in the model of local convection.

Particle-phase dry deposition and air–soil gas exchange of polycyclic aromatic hydrocarbons (PAHs) in Izmir, Turkey

Ambient air and dry deposition samples were collected at suburban and urban sites in Izmir, Turkey. Atmospheric total (particle+gas) ∑14PAHs concentrations were 36±39 and 144±163ngm−3 for suburban and urban sites, respectively. Phenanthrene was the most abundant compound at all sites, and all samples were dominated by low molecular weight PAHs. Average particulate ∑14PAH dry deposition fluxes were 8160±5024 and 4286±2782ngm−2 day−1 and overall average particulate dry deposition velocities were 1.5±2.4 and 1.0±2.3cms−1 for suburban and urban sites, respectively. Soil samples were collected at suburban site. Average soil concentration for ∑14PAH was 55.9±14.4ngg−1 dry weight. Calculated gas-phase air–soil exchange fluxes indicated that fluorene, phenanthrene, anthracene, and carbazole were deposited to soil in winter while they were volatilized in summer. Other compounds (fluoranthene-benzo[g,h,i]perylene) were deposited to soil in both periods. Annual average fluxes of PAHs representing soil to air (i.e., gas volatilization) and air to soil transfer (i.e., gas absorption, dry deposition, and wet deposition) processes were also compared. All processes were comparable for Σ14PAHs however their input was dominated by gas absorption. Gas absorption dominated for lower molecular weight PAHs, however dry deposition dominated for higher molecular weight PAHs. The results have suggested that for fluorene, soil and air may be approaching a steady state condition. For the remaining compounds, there was a net accumulation into the soil.

Seasonal atmospheric deposition variations of polychlorinated biphenyls (PCBs) and comparison of some deposition sampling techniques

Ambient air and bulk deposition samples were collected between June 2008 and June 2009. Eighty-three polychlorinated biphenyl (PCB) congeners were targeted in the samples. The average gas and particle PCB concentrations were found as 393 ± 278 and 70 ± 102pg/m(3), respectively, and 85% of the atmospheric PCBs were in the gas phase. Bulk deposition samples were collected by using a sampler made of stainless steel. The average PCB bulk deposition flux value was determined as 6,020 ± 4,350pg/m(2)day. The seasonal bulk deposition fluxes were not statistically different from each other, but the summer flux had higher values. Flux values differed depending on the precipitation levels. The average flux value in the rainy periods was 7,480 ± 4,080pg/m(2)day while the average flux value in dry periods was 5,550 ± 4,420pg/m(2)day. The obtained deposition values were lower than the reported values given for the urban and industrialized areas, yet close to the ones for the rural sites. The reported deposition values were also influenced by the type of the instruments used. The average dry deposition and total deposition velocity values calculated based on deposition and concentration values were found as 0.23 ± 0.21 and 0.13 ± 0.13cm/s, respectively.

Dry and wet particle deposition of polybrominated diphenyl ethers (PBDEs) in Guangzhou and Hong Kong, South China

PBDEs were measured in wet and dry particle deposition samples collected at the urban sites of Guangzhou and Hong Kong from December 2003 to December 2004. The depositional fluxes of BDE-209 ranged from 273 to 6000 ng m(-2) day(-1) in Guangzhou and from 29.1 to 1100 ng m(-2) day(-1) in Hong Kong. The depositional fluxes for Sigma(9)PBDEs (defined as the sum of BDE-28, -47, -66, -100, -99, 154, -153, -138 and -183) ranged from 0.96 to 604 ng m(-2) day(-1) in Guangzhou and from <LOD to 10.6 ng m(-2) day(-1) in Hong Kong. BDE-209 was the most abundant PBDE congener, showing that deca-BDE accounts for most of the total PBDE emitted in the environment. Distinct seasonal patterns were observed in the PBDE depositional fluxes in Hong Kong, with higher depositional fluxes during the winter monsoon period and lower fluxes during the summer. The air mass back trajectory analysis showed that the high concentrations of PBDEs in deposition samples in Hong Kong originated from the inland of the Pearl River Delta (PRD) region. With the exception of the highest depositional flux of BDE-209 observed during the periods of haze, the seasonal variation in the BDE-209 depositional fluxes in Guangzhou was less strong, suggesting the importance of local sources. The average dry deposition velocities of BDE-47, -99, and -209 were 0.32 +/- 0.12 cm s(-1), 0.24 +/- 0.16 cm s(-1), and 0.28 +/- 0.01 cm s(-1), respectively. The particle washout ratios (W(p)) of PBDEs decreased with increasing rainfall frequency and reached a consistent level afterwards. The median washout ratios of BDE-47, -99 and -209 were 1.1 x 10(5), 3.1 x 10(5), and 5.1 x 10(5), respectively.

Characterization of Ambient Air Particulates and Particulate Mercury at Sha-Lu, Central Taiwan

Ambient air samples were collected between December 9, 2008, and January 14, 2009, at a highway traffic site located in Sha-Lu, central Taiwan. Atmospheric particulates and particulate bound mercury Hg(p) dry deposition, concentrations and dry deposition velocities were also studied. The objective of this study was to: 1) estimate the dry deposition concentrations of ambient air particulates and Hg(p) following 1- and 2-day sampling events using the total suspended particulates (TSP) sampler, and dry deposition plate (DDP) data; and 2) compare Hg(p) concentrations and dry deposition using two different media (i.e., quartz filter and projection film). The results obtained using overhead projection film as collection medium indicated that the average ambient air particulates dry deposition fluxes for the 1- and 2-day periods were 65.99 and 87.88 μ g/min m2, respectively. The corresponding fluxes using quartz filter collection medium were 67.31 and 52.53 μ g/min m2, respectively. Previous Hg related depositional studies have commonly used quartz filter as a collection media; however, in the work reported here overhead projection film was chosen due to its low cost as one of the collection medium, and the results obtained have been compared with the those estimated using quartz. Using the overhead projection collection medium, the average ambient air particulates dry deposition velocities for 1- and 2-day periods were 2.02 and 2.70 cm/sec, respectively, and the corresponding velocities with quartz film collection medium were 1.85 and 1.41 cm/sec, respectively. The overhead projection film collection medium results indicated that the average ambient air particulates bound Hg(p) dry deposition fluxes for the 1- and 2-day periods were 0.16 and 0.09 ng/min m2, respectively, and the corresponding fluxes estimated using the quartz filter collection medium were 0.21 and 0.11 ng/min m2, respectively. The average Hg(p) concentrations ranged from 0.04 to 0.86 ng/m2. The average ambient air particulates bound Hg(p) dry deposition velocities using the overhead projection collection medium for the 1- and 2-day periods were 6.79 and 3.32 cm/sec, respectively, and the corresponding velocities using quartz film collection medium were 8.94 and 4.41 cm/sec, respectively. In addition, the Hg(p) values associated with plant obtained in this study help to establish Hg(p) background concentrations in the air of specific area and also help to establish additional sources of Hg(p) link to distinct pollution events in Taiwan.

Processes affecting the movement of organochlorine pesticides (OCPs) between soil and air in an industrial site in Turkey

Soil and atmospheric concentrations, dry deposition and soil-air gas exchange of organochlorine pesticides (OCPs) were investigated at an industrial site in Aliaga, Izmir, Turkey. Current-use pesticides, endosulfan and chlorpyrifos, had the highest atmospheric levels in summer and winter. Summertime total (gas + particle) OCP concentrations in air were higher, probably due to increased volatilization at higher temperatures and seasonal local/regional applications of current-use pesticides. Particle deposition fluxes were generally higher in summer than in winter. Overall average dry particle deposition velocity for all the OCPs was 4.9 ± 4.1 cm s −1 (average ± SD). ΣDDXs (sum of p,p′-DDT, p,p′-DDD, and p,p′-DDE) were the most abundant OCPs in Aliaga soils ( n = 48), probably due to their heavy historical use and persistence. Calculated fugacity ratios and average net gas fluxes across the soil-air interface indicated volatilization for α-CHL, γ-CHL, heptachlorepoxide, cis-nonachlor, trans-nonachlor, and p,p′-DDT in summer, and for α-CHL, γ-CHL, trans-nonachlor, endosulfan sulfate, and p,p′-DDT in winter. For the remaining OCPs, soil acted as a sink during both seasons. Comparison of the determined fluxes showed that dry particle, gas-phase, and wet deposition are significant OCP input mechanisms to the soil in the study area.

Sulfur dioxide in the tropical marine boundary layer: dry deposition and heterogeneous oxidation observed during the Pacific Atmospheric Sulfur Experiment

Research flights with the National Center for Atmospheric Research (NCAR) C-130 airborne laboratory were conducted over the equatorial ocean during the Pacific Atmospheric Sulfur Experiment (PASE). The focused, repetitive flight plans provided a unique opportunity to explore the principal pathways of sulfur processing in remote marine environments in close detail. Fast airborne measurements of SO2 using the Drexel University APIMS (Atmospheric Pressure Ionization Mass Spectrometer) instrument further provided unprecedented insight into the complete budget of this important sulfur gas. In general, turbulent mixing in the marine boundary layer (MBL) continuously depletes SO2 due to the shallow convection of the tropical trade wind regime by venting the gas into the buffer layer (BuL) above. However, on nearly one-third of the flights a net import of SO2 into the MBL from the BuL was observed. Concurrent measurements of the DMS budget allowed for a heterogeneous S(IV) oxidation rate to be inferred from the SO2 budget residual. The average heterogeneous loss rate was found to be 0.05 h−1, which taken in conjunction with the observed aerosol surface area distributions and O3 levels indicates that the supermicron aerosols maintain a near neutral pH. The average dry deposition velocity of SO2 was found to be 0.4 cm s−1, about 30% lower than predicted by standard parameterizations. The yield of SO2 from DMS oxidation was found to be near unity. The mission averages indicate that approximately 57% of the SO2 in the MBL is lost to aerosols, 27% is subject to dry deposition, 7% is mixed into the BuL, and 10% is oxidized by OH.