Average Dry Deposition Fluxes Research Articles

Atmospheric (Dry + Wet) Deposition of PCDD/Fs in Taiwan

Air pollution was getting worse and worse with the development of economic, and atmospheric deposition was an important mechanic for the removal of air pollutants. During 2017, the average dry deposition fluxes of total-PCDD/Fs-WHO2005-TEQ in various areas in Taiwan range between 57 (Lienchiang County in autumn) and 589 pg WHO2005-TEQ m–2 month–1 (Keelung City in winter), with an average of 221 pg WHO2005-TEQ m–2 month–1. The average total deposition fluxes of total-PCDD/Fs-WHO2005-TEQ in various areas in Taiwan range between 65 (Lienchiang County in autumn) and 681 pg WHO2005-TEQ m–2 month–1 (Keelung City in winter), with an average of 263 pg WHO2005-TEQ m–2 month–1. The fractions of dry deposition fluxes contribute to the total deposition fluxes range between 37.8% (Yilan County in winter) and 99.9% (Kaohsiung City in winter), with an average of 82.1%.

Seasonal Patterns of Dry Deposition at a High‐Elevation Site in the Colorado Rocky Mountains

AbstractIn the Colorado Rocky Mountains, high‐elevation barren soils are deficient in carbon (C) and phosphorus (P) and enriched in nitrogen (N). The seasonal variability of dry deposition and its contributions to alpine elemental budgets is critical to understanding how dry deposition influences biogeochemical cycling in high‐elevation environments. In this 2 year study, we evaluated dry and wet deposition inputs to the Niwot Ridge Long Term Ecological Research (NWT LTER) site in the Colorado Rocky Mountains. The total organic C flux in wet + dry (including soluble and particulate C) deposition was >30 kg C ha−1 yr−1 and represents a substantial input for this C‐limited environment. Our side‐by‐side comparison of dry deposition collectors with and without marble insert indicated that the insert improved retention of dry deposition by ~28%. Annual average dry deposition fluxes of water‐soluble organic carbon (4.25 kg C ha−1 yr−1) and other water‐soluble constituents, including ammonium (0.16 kg NH4+ha−1 yr−1), nitrate (1.99 kg NO3− ha−1 yr−1), phosphate (0.08 kg PO43− ha−1 yr−1), and sulfate (1.20 kg SO42− ha−1 yr−1), were comparable to those in wet deposition, with highest values measured in the summer. Backward trajectory analyses implicate air masses passing through the arid west and Four Corners, USA, as dominant source areas for dry deposition, especially in spring months. Synchronous temporal patterns of deposition observed at the NWT LTER site and a distant Rocky Mountain National Park Clean Air Status and Trends Network site indicate that seasonal dry deposition patterns are regional phenomena with important implications for the larger Rocky Mountain region.

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.

The sources of trace element pollution of dry depositions nearby a drinking water source.

Miyun Reservoir is one of the most important drinking water sources for Beijing. Thirteen atmospheric PM sampling sites were established around this reservoir to analyze the mineral composition, morphological characteristics, element concentration, and sources of atmospheric PM pollution, using transmission electron microscope, X-ray diffraction, and inductively coupled plasma mass spectrometry analyses. The average monthly dry deposition flux of aerosols was 15.18g/m2, with a range of 5.78-47.56g/m2. The maximum flux season was winter, followed by summer, autumn, and spring. Zn and Pb pollution in this area was serious, and some of the sample sites had Cr, Co, Ni, and Cu pollution. Deposition fluxes of Zn/Pb in winter and summer reached 99.77/143.63 and 17.04/33.23g/(hm2 month), respectively. Principal component analysis showed two main components in the dry deposition; the first was Cr, Co, Ni, Cu, and Zn, and the other was Pb and Cd. Principal sources of the trace elements were iron mining and other anthropogenic activities in the surrounding areas and mountainous area north of the reservoir. Mineralogy analysis and microscopic conformation results showed many iron minerals and some unweathered minerals in dry deposition and atmospheric particulate matter, which came from an iron ore yard in the northern mountainous area of Miyun County. There was possible iron-rich dry deposition into Miyun Reservoir, affecting its water quality and harming the health of people living in areas around the reservoir and Beijing.

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).

Effects of Asian dust on the atmospheric input of trace elements to the East China Sea

The long-range transport of Asian dust (AD) can carry large quantities of trace elements to the marginal seas of the Northwest Pacific, and the deposition of soluble fractions of aerosol elements may significantly impact the primary productivity and ecosystem structure. Samples of total suspended particulates (TSP) and size-segregated aerosols were collected synchronously at Huaniao Island in the East China Sea (ECS) between April 2010 and March 2011 and then analyzed for the total and soluble fractions of 14 trace elements. Twelve AD events were identified in the spring and autumn of the sampling year based on official records of AD storms from the China Meteorological Administration and verified by the high Al concentration in the aerosol samples. The dry deposition flux of the total or soluble fraction of each analyzed aerosol element was estimated using its concentration in the TSP samples and dry deposition velocity derived from the size-segregated samples. The dry deposition velocity varied from 0.7cms−1 for total Pb to 1.5cms−1 for total Al based on the mass median diameters (MMD) of 1.6 and 4.9μm, respectively, of associated particles. During AD events, the mean concentrations of the total and soluble fractions of Al, Fe, Mn, P and Ba increased significantly and led to enhanced dry deposition fluxes of these elements to the ECS (over a factor of 3 for the total and over 30% for the soluble fraction). The concentrations of the soluble fractions of anthropogenically derived elements (As, Cd, Cu, Pb, V and Zn) during AD events were lower than at other times and resulted in lower dry deposition fluxes. Asian dust events were associated with higher than average dry deposition fluxes of soluble Fe and P and lower fluxes of soluble Cu and Zn.

Measuring metallic elements of total suspended particulates (TSPs), dry deposition flux, and dry deposition velocity for seasonal variation in central Taiwan

The purposes of this study were to investigate and characterize ambient air particulate concentrations and dry deposition fluxes and those metallic elements associated with them in central Taiwan during 2009–2010. At the Bei-Shi (suburban/coastal) sampling site, the average TSP concentrations, flux, and deposition velocity were 92.3 (μgm−3), 165.92 (μgm−2min−1), and 3 (cms−1), respectively. In addition, at the Quan-Xin (industrial) sampling site, the highest average TSP concentrations of As, ambient air particulate bound mercury (Hg(p)), Mn, Fe, Zn, Cr, Cu and Pb were 3.56, 0.07, 82.21, 2769.82, 109.33, 31.93, 109.76 and 39.15ngm−3, respectively. The highest average dry deposition flux of elements As, Hg(p), Mn, Fe, Zn, Cr, Cu and Pb were 2.36, 0.15, 18.11, 303.8, 35.59, 18.66, 45.47 and 42.6 (ngm−2min−1), respectively in Quan-Xin (industrial). The median deposition velocity (Vd) of metallic elements was present at the five characteristic sampling sites, respectively. However, the median dry deposition velocity (Vd) of Hg(p) was 2.73–4.78cms−1, higher than all other elements in the five characteristic sampling sites during 2009–2010. The median dry deposition velocity (Vd) of Fe was 0.17–0.27cms−1, lower than all other elements in the five characteristic sampling sites during 2009–2010.

Atmospheric Deposition Modeling of Polychlorinated Dibenzo-p-dioxins, Dibenzofurans and Polychlorinated Biphenyls in the Ambient Air of Southern Taiwan. Part I. Dry Depositions

Atmospheric deposition, including dry and wet deposition, is a primary pathway for the transfer of POPs to terrestrial and aquatic ecosystems. In this study (that is, the part I.), the characteristics of PCDD/Fs and PCBs in the ambient air of Tainan City were simulated by the PM_(10) versus PCDD/Fs concentration regression analysis, gas-particle partition modeling, and the simulation of dry deposition. Dry deposition fluxes are obtained from the combination of the PCDD/F and PCB concentrations, meteorological information, dry deposition velocities, and scavenging ratios. The dry deposition fluxes of PCDD/F-TEQ2005 increase with decreasing temperature, while increase with a higher degree of chlorine numbers on PCDD/F homologues. In this study (that is, the part I.), the average PCDD/F dry deposition fluxes in spring, summer, fall and winter were 69.3, 28.2, 129 and 246 pg WHO-TEQ/m^2-month during 2012, respectively. As for 2013, the average PCDD/F dry deposition fluxes in spring, summer, fall and winter were 67.0, 29.8, 102 and 377 pg WHO-TEQ/m^2-month, respectively. The average PCB dry deposition fluxes in spring, summer, fall and winter were 2.16, 1.99, 5.70 and 11.9 pg WHO-TEQ/m^2-month during 2012, respectively. As for 2013, the average PCB dry deposition fluxes in spring, summer, fall and winter were 2.11, 1.27, 4.49 and 8.88 pg WHO-TEQ/m^2-month, respectively. The minimum simulated value occurred in summer, while the maximum dry deposition fluxes, which were about 4-5 times higher than the minimum values, occurred in winter. The lower values observed in summer may be caused by the atmospheric diffusion of SVOCs and high rainfall intensity.

Atmospheric Arsenic Deposition in Chiayi County in Southern Taiwan

Although arsenic contamination of underground water in southern Taiwan is well known, few studies examine atmospheric arsenic deposition in this area, which might be the major source of such pollution to the soil, water, and even underground water. This research focused on the atmospheric arsenic concentration, dry and wet depositions, and the As distribution around Chiayi County, located in the south of Taiwan. Eight sampling sites are used, both upwind and downwind of an area with heavy industrial and human activities. All samples were collected by a PS-1 high volume sampler at each site, pretreated by a digestion process, and further analyzed with an ICP-MS. The results show that the arsenic deposition flux ranged from 65.0 to 473 μg/m2-month in Chiayi County. This deposition flux has no significant seasonal variation, based on the multiple trend results obtained from pooling the dry and wet deposition data. The average dry deposition flux of As ranged from 34 to 161 μg/m2-month during the sampling year, and had the opposite trend to the wind speed. Additionally, the correlations between atmospheric arsenic concentration and PM levels were significant, supported by the low p-value (< 0.01) at a 99% confidence level. Meanwhile, the highly linear correlation between As and PM concentrations was also evaluated. The amount of precipitation was statistically correlated to the wet deposition flux (11.3–414 μg/m2-month with a p-value = 2 × 10–7 and r-value = 0.9306. Furthermore, the composition of the As mass concentrations in ambient air were dominated by As (V) in both fall (66.4%) and winter (68.9%). According to the GIS spatial analysis of the As concentration in the dry season, from October to March, the As contribution of local emissions were not significant. Consequently, this study indicates that the atmospheric As around Chiayi County might be sourced from the upwind northern area, and mainly deposited through wet scavenging.

Size-Dependent Dry Deposition of Airborne Polybrominated Diphenyl Ethers in Urban Guangzhou, China

Gaseous and size-segregated particulate PBDEs (specifically BDE-47, -99, -183, -207, and -209) in the air were measured in urban Guangzhou at 100 and 150 m above the ground in daytime and at night in August and December 2010, to assess dry deposition of these contaminants accurately with regards to influences of meteorological factors but without confounding surface effects. Particulate PBDEs were more abundant at night than in daytime, and slightly higher in winter than in summer, likely from varying meteorological conditions and atmospheric boundary layers. More than 60% of particulate-phase PBDEs was contained in particles with an aerodynamic diameter (D(p)) below 1.8 μm, indicating long-range transport potential. The average daily particle dry deposition fluxes of PBDEs in August ranged from 2.6 (BDE-47) to 88.6 (BDE-209) ng m(-2) d(-1), while those in winter ranged from 2.0 (BDE-47) to 122 (BDE-209) ng m(-2) d(-1). Deposition fluxes of all PBDE congeners were significantly higher in daytime than at night for both months, due to the effect of diurnal variability of meteorological factors. In addition, mean overall particle deposition velocities of individual BDE congeners ranged from 0.11 to 0.28 cm s(-1). These values were within a factor of 2 of assumed values previously used in southern China and the Laurentian Great Lakes, suggesting that such assumptions were reasonable for sites with similar particulate size distributions and PBDE sources. Dry deposition velocities of PBDEs were lower at night than those in the daytime, probably reflecting higher mechanical and thermal turbulence during daytime. Dry deposition of particulate-bound PBDEs is influenced by short-term temporal variability from meteorological factors, and also by particulate size fractions.

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.

Atmospheric Dry Deposition of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans (PCDD/Fs) and Polychlorinated Biphenyls (PCBs) in Southern Taiwan

Dry deposition is one of the major routes by which air pollutants enter the ecosystem, and thus this study investigated the dry deposition characteristics of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and biphenyls (PCBs) in the ambient air of industrial, urban, and rural areas in southern Taiwan from November 2010 to May 2011. Average dry deposition fluxes of total PCDD/Fs and PCBs in the ambient air of four sites were 157-544 pg/m2-day (8.30-27.5 pg ITEQ/ m^2-day) and 289-1010 pg/m^2-day (0.540-1.94 pg WHO-TEQ/m^2-day), respectively. The results showed that particle phase depositions dominated the dry deposition processes for the removal of PCDD/Fs and PCBs from the atmosphere, and the atmospheric deposition flux in the cold season tended to be higher than that during the warm season. The dry deposition velocity of individual PCDD/Fs (0.031-0.546 cm/s) increased as the number of chlorinated substitutes increased, which were similar to those measured or predicted in other Asian countries. Similar patterns of dry deposition velocities were observed for individual PCBs (0.069-3.38 cm/s), due to the fact that low chlorinated PCBs are predominant in gas phase and have lower deposition velocities.

Determination of the Sampler Type and Rainfall Effect on the Deposition Fluxes of the Polychlorinated Biphenyls

Atmospheric concentration and deposition samples were collected between June 2008 and June 2009 in an urban sampling site Yavuzselim, Turkey. Eighty-three polychlorinated biphenyl (PCB) congeners were targeted in the collected samples. It was found that 90% of the total PCB concentration was in the gas phase. Deposition samples were collected by a wet-dry deposition sampler (WDDS) and a bulk deposition sampler (BDS). Average total deposition fluxes measured with the BDS in dry periods was 5500 ± 2400 pg/(m2day); average dry deposition fluxes measured by the WDDS in the same period were 6400 ± 3300 pg/(m2day). The results indicated that the sampler type affected the measured flux values. Bulk deposition samples were also collected in rainy periods by using the BDS and the average flux value was 8700 ± 3100 pg/(m2day). The measured flux values were lower than the values reported for the urban and industrial areas. Dry deposition velocities for the WDDS and BDS samples were calculated 0.48 ± 0.35 cm/s and 0.13 ± 0.15 cm/s, 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.

Evaluation of SO&lt;SUB align=right&gt;2 dry deposition over a cassava plantation in Rayong, Thailand

SO2 emissions have become a significant problem in the East Asian region. Long term exposure to high SO2 concentration can affect human health and the environment. Approximately half of the SO2 is delivered to the earth by the dry deposition process; the other half is deposited by wet deposition. Thus, an assessment of SO2 dry deposition is necessary for understanding its qualitative and quantitative effects. In the research program described here, SO2 dry deposition was studied in terms of SO2 dry deposition flux and deposition velocity using the Bowen ratio technique. All necessary parameters were measured above a cassava plantation at a site in Rayong, Thailand during the period from June to September 2004. The Bowen ratio technique was most applicable during the 8:00 to 17:00 time period of each day. The results yield an average transfer coefficient of 10.6 cm/s, relevant to the height interval across which differences were measured. The average dry deposition flux was 0.17 mg/m²/hr and the average dry deposition velocity was 0.14 cm/s.

Measurement of atmospheric deposition of polychlorinated biphenyls and their dry deposition velocities in an urban/industrial site in Turkey

Dry deposition fluxes and total (gas+particle) concentrations of polychlorinated biphenyls (PCBs) were measured between August 2004 and May 2005. Samples were collected from an urban-industrial site of Bursa, Turkey. A stainless steel pot and a high volume air sampler (HVAS) were employed to collect deposition and ambient air samples, respectively. The dry deposition fluxes of PCBs ranged from 3600 to 56,000 pg m−2 d−1 while the total PCB concentrations collected simultaneously were between 35 and 348 pg m−3. The average dry deposition flux value was in line with the previously reported values. Possible variations in PCB fluxes were likely due to PCB and total suspended particle (TSP) concentrations, and meteorological conditions. No seasonal trends were observed for the bulk deposition samples. The 3- and 4- chlorobiphenyls (CBs) were abundant homolog groups in bulk and concentration samples with ratios of 67% and 90%, respectively. Apparent bulk deposition velocities were calculated by dividing the dry deposition flux value by particle phase air concentration values of PCBs measured with HVAS. The calculated apparent dry deposition velocities ranged from 0.23 cm s−1 to 3.09 cm s−1 (aver ± SD, 0.74 ± 0.23 cm s−1).

Atmospheric Dry Deposition Fluxes of Metallic Pollutants in Asia During 1997–2006

Numerous studies have monitored deposition velocity and dry deposition fluxes in Asia throughout the recent decade. This study compares different sample collections, pretreatments, and analytical methods utilized throughout the past decade in Asia. Analytical results suggest that the primary dry deposition sources are traffic and soil exhaust. This study also elucidates the sources, analytical tools, and the average concentrations in the Asian region for dry deposition and related metallic elements during 1997–2006. The order of metallic elements in average dry deposition fluxes in Asia was established as: Na > K > Mg > Fe > Ca > Zn > Pb > Mn > Cl > Cu > Cd > Cr, and in average atmospheric concentrations the order was observed as: Ca > Cl > Na > Fe > Mg > K > Zn > Cu > Pb > Mn > Cr > Cd. The order of metallic elements in average deposition velocity in Asia was Fe > Zn > Cd > Ca > Mn > Pb > Cr > Cu > Mg > Na > Cl > K.

Ambient air dry deposition and ionic species analysis by using various deposition collectors in Shalu, central Taiwan

This study describes the chemical composition of dry deposition collected at a highway traffic site in central Taiwan during daytime and nighttime periods by using a dry deposition plate (DDP) and water surface sampler (WSS). In addition, the characterization for mass and water-soluble species of total suspended particulate (TSP), both PM 2.5 and PM 10, was studied at the study site from August 22 to November 30, 2006. Dry deposition fluxes of ambient air particulates and inorganic species (Na +, NH 4 +, K +, Mg 2+, Ca 2+, Cl −, NO 3 − and SO 4 2−) were analyzed by Ion Chromatography (DIONEX-100). Results of the particulate dry deposition fluxes and mass concentrations are higher in the water surface sampler with respect to the dry deposition plate used in this study. Statistical results also showed the average dry deposition flux of the ionic species (Na +, NH 4 +, K +, Cl −, NO 3 − and SO 4 2−) obtained by the DDP and WSS displayed significant differences. Also, the average concentrations of Mg 2+ and, Ca 2+ were statistically the same at this study site.

A modified technique for field measurements of dry deposition fluxes of polychlorinated biphenyls in tropical regions

This report focused on the development of a technique to measure dry deposition fluxes of PCBs in tropical environments. Temperature resistant double-adhesive tape has been used as a new surrogate surface for collection of deposited PCBs. The new technique includes the measurement of field blanks for the entire sampling period. A sonication-assisted extraction procedure has been validated for the extraction of PCBs from the tape. The new technique has been used in the field for a period of 4 months in the tropical region of Singapore. The average dry deposition flux measured for total PCBs was 15.3 ng m(-2) day(-1) and, on a global scale, this can be considered to be low.

Particle-Phase Dry Deposition and Air−Soil Gas-Exchange of Polybrominated Diphenyl Ethers (PBDEs) in Izmir, Turkey

The particle-phase dry deposition and soil-air gas-exchange of polybrominated diphenyl ethers (PBDEs) were measured in Izmir, Turkey. Relative contributions of different deposition mechanisms (dry particle, dry gas, and wet deposition) were also determined. BDE-209 was the dominating congener in all types of samples (air, deposition, and soil). Average dry deposition fluxes of total PBDEs (sigma7PBDE) for suburban and urban sites were 67.6 and 128.8 ng m(-2) day(-1), respectively. Particulate dry deposition velocities ranged from 11.5 (BDE-28) to 3.9 cm s(-1) (BDE-209) for suburban sites and 7.8 (BDE-28) to 2.8 cm s(-1) (BDE-154) for urban sites with an overall average of 5.8 +/- 3.7 cm s(-1). The highest sigma7PBDE concentration (2.84 x 10(6) ng kg(-1) dry wt) was found around an electronic factory among the 13 soil samples collected from different sites. The concentration in a bag filter dust from a steel plant was also high (2.05 x 10(5) ng kg(-1)), indicating that these industries are significant PBDE sources. Calculated net soil-air gas exchange flux of sigma7PBDE ranged from 11.8 (urban) to 23.4 (industrial) ng m(-2) day(-1) in summer, while in winter it ranged from 3.2 (urban) to 11.6 (suburban) ng m(-2) day(-1). All congeners were deposited at all three sites in winter and summer. It was estimated that the wet deposition also contributes significantly to the total PBDE deposition to soil. Dry particle, wet, and gas deposition contribute 60, 32, and 8%, respectively, to annual PBDE flux to the suburban soil.