Atmospheric Washout Research Articles

Spatial distribution of iodine in the pedosphere of China and its influencing factors

The China Geochemical Baseline project (2008–2013) obtained a large amount of reliable baseline data on 76 elements, including iodine, from 3381 top (0–25 cm) and 3380 deep (>100 cm) alluvial soil or sediment samples. Iodine concentrations, ranging from 0.01 to 21.58 mg/kg in the top samples (TS) and 0.01 to 28.30 mg/kg in the deep samples (DS), were determined using colorimetry under strict quality control. The median values of iodine, which were considered geochemical baseline values in the TS and DS, were 1.10 and 0.99 mg/kg, respectively, and the mean values were 1.45 and 1.43 mg/kg, respectively. The majority of the iodine in the pedosphere is obtained from the atmosphere, which in turn is obtained from the oceans. The mobility of iodine in different media was determined by its geochemical behavior. Iodine distribution maps indicated that low iodine concentrations below Q25 (<0.65 and 0.56 mg/kg in TS and DS, respectively) are primarily distributed in Northwest China, Tibet, and Sichuan, which could be mainly attributed to significant atmospheric washout and/or distance from the sea and low iodine fixing capacity of inland deserts. High concentrations are scattered throughout the country and are influenced by various factors, including atmospheric precipitation, soil composition, and mineral distribution, exploitation, and utilization. After the advent of salt iodization in 1995, iodine deficiency disorders have been largely eliminated from China. Although the heavily diseased areas correspond to some low iodine concentration areas, the distribution of the overall iodine deficiency disease areas from before salt iodization, compared using geochemical maps, is not correlated to the distribution of iodine concentration in the soil. These new TS and DS data and iodine geochemical maps provide a deep insight into the factors controlling the distribution of iodine in the pedosphere of China and significantly improve the global database of iodine in soils.

Chemical Composition and Source Apportionment of Total Suspended Particulate in the Central Himalayan Region

The present study analyzes data from total suspended particulate (TSP) samples collected during 3 years (2005–2008) at Nainital, central Himalayas, India and analyzed for carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)) and inorganic species, focusing on the assessment of primary and secondary organic carbon contributions (POC, SOC, respectively) and on source apportionment by positive matrix factorization (PMF). An average TSP concentration of 69.6 ± 51.8 µg m−3 was found, exhibiting a pre-monsoon (March–May) maximum (92.9 ± 48.5 µg m−3) due to dust transport and forest fires and a monsoon (June–August) minimum due to atmospheric washout, while carbonaceous aerosols and inorganic species expressed a similar seasonality. The mean OC/EC ratio (8.0 ± 3.3) and the good correlations between OC, EC, and nss-K+ suggested that biomass burning (BB) was one of the major contributing factors to aerosols in Nainital. Using the EC tracer method, along with several approaches for the determination of the (OC/EC)pri ratio, the estimated SOC component accounted for ~25% (19.3–29.7%). Furthermore, TSP source apportionment via PMF allowed for a better understanding of the aerosol sources in the Central Himalayan region. The key aerosol sources over Nainital were BB (27%), secondary sulfate (20%), secondary nitrate (9%), mineral dust (34%), and long-range transported mixed marine aerosol (10%). The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analyses were also used to identify the probable regional source areas of resolved aerosol sources. The main source regions for aerosols in Nainital were the plains in northwest India and Pakistan, polluted cities like Delhi, the Thar Desert, and the Arabian Sea area. The outcomes of the present study are expected to elucidate the atmospheric chemistry, emission source origins, and transport pathways of aerosols over the central Himalayan region.

Atmospheric washout of 35S during single rain events – Implications for 35S sampling schemes

Cosmogenic radiosulfur (35S; half-life: 87.4 days) is transferred with the rain to the groundwater (as 35SO42−) and can be used as residence time tracer for the detection of sub-yearly groundwater residence times. Due to the distinct but non-regular annual 35S pattern in precipitation, related data evaluation requires consideration of a35S input function that is based on representative rain samples. While minor rain events can easily be sampled quantitatively and hence representatively, a long-lasting rain event may get documented by a sample that represents only a certain sequence of the event, thus potentially resulting in a35S activity concentration that might not be representative. With the aim to examine the magnitude of temporal variations of the 35S activity concentration in rain during long-lasting rain events, we present and discuss two related exemplary 35S time series. Furthermore, we evaluate the applicability of the parameters total sulfate and electrical conductivity (EC), both detected in rainwater as easily attainable 35S proxies. The results of the study show (i) that the 35S activity concentration may vary substantially during long-lasting rain events due to atmospheric migration processes and aerosol washout and (ii) that neither sulfate nor EC are suitable as 35S proxies due to the different origin of 35S on the one hand and sulfate/EC on the other. Hence, for the determination of a35S activity concentration that is representative for a long-lasting rain event 35S analyses of an adequate number of sub-samples cannot be avoided.

Phenomenology and geographical gradients of atmospheric deposition in southwestern Europe: Results from a multi-site monitoring network

This article presents the results of atmospheric deposition from a 15-sites network which cover remote, agricultural, urban and industrial areas in the Iberian Peninsula and the Balearic Islands, with the aim of exploring geographical, climatic and natural vs anthropogenic gradients. Annual average fluxes of global deposition, discriminating insoluble (3,5–20,7 g m−2 year−1) and soluble-inorganic (7,1–45,5 g m−2 year−1) aerosols are discussed, seasonal patterns are regarded, and an attempt to estimate the impact of the main sources is presented. The wide range of atmospheric deposition fluxes (DF) regarding soluble (DFSOL) and insoluble (DFINS) has been investigated taking into consideration the contribution from nearby to long-distance sources, such as African dust, or regional-to-nearby ones, which include agricultural dust in the Ebro Valley, industrial emissions at different parts, urban dust at all cities, or saline dust resuspension from a dissicated lake bed.DFSOL is made up of marine aerosols, prevailing in coastal areas, with few exceptions in the Ebro Valley; nitrogen-species, homogeneously distributed across the network, with few exceptions due to agricultural sources; mineral dust, enhanced in the Ebro Valley owing to regional and agricultural emissions; and phospathe, displaying comparable values to other studies in general, but three hotspots at regional background environments have been identified.DFINS particles followed the aridity pattern, especially where anthropogenic emissions take place. Our estimates indicate that the regional dust to DFINS in the Ebro Valley represented 23–30%, overpassing 50% at intensive agricultural areas. Similarly, urban-metropolitan contributions accounted for 37–45% at the four cities, and 55% at the industrial one. African dust deposition was enhanced in the Central Pyrenees (75–80%) as a result of the magnification of atmospheric washout processes, and in south-eastern Iberia (69%) owing to the higher frequency of dust outbreaks.

Influence of electric charges on the washout efficiency of atmospheric aerosols by raindrops

Latest investigation completed at IRSN has revealed the substantial influence of flow morphology around the drops, in atmospheric washout of fine aerosol particles by precipitations, in complement to classical mechanisms. Moreover, several authors have claimed that rain drops during stormy rainfall carry millions of elementary electric charges which could increase by couple orders of magnitude the collection efficiency as a consequence of electrostatic forces. In non-thunderstorm clouds, model calculations indicate that the image charge effect resulting from aerosol charging can significantly affect their washout, even by uncharged raindrops.However, investigations on the influence of electric charges on aerosol washout (or collection efficiency) by simulated raindrops are very fragmented and contradictory.In this article, we report results of self-charged water drop generated by hypodermic needle over charge values comparable to those reported in the literature during stormy rainfall. We also controllably charged aerosol particles by corona discharge and evaluate how it affects their collection efficiency. Electric charges on drops and aerosols are precisely monitored by high resolution electrometers. Our preliminary results tend to accredit the impact of electric charges in collection efficiency.

Assessment of 7Be content in precipitation in a South American semi-arid environment

There are two naturally occurring radiogenic isotopes of beryllium, 7Be and 10Be. These are produced when cosmic radiation interacts with oxygen and nitrogen in the atmosphere. After production, these radionuclides are input to ecosystems through wet and dry deposition. In recent years 7Be and 10Be have proved to be powerful tools for studying dynamic processes that occur on the surface of the earth. We measured the 7Be content in precipitation at a semiarid location in central Argentina. From November 2006 to March 2009, 68 precipitation events were collected. Measured 7Be content ranged from 0.7±0.4BqL−1 to 3.2±0.7BqL−1, with a mean of 1.7BqL−1±0.6BqL−1. Beryllium-7 content of rainfall did not show clear relationships with amount of rainfall (mm), mean intensity (mmh−1) or duration (h−1), or elapsed time between events (day). The general results indicate that for the typical range of precipitation there was no atmospheric washout and that the reload of the atmosphere is not a relevant factor, but when the amount of precipitation is very high washout may occur. On the other hand, when the 7Be content was measured during single rain events, a high content of this radionuclide was found to be associated with very low rainfall intensity (≈3mmh−1), this suggests that rain intensity could affect the 7Be content. Using all data, a good linear relationship between 7Be deposition and rain magnitude was obtained (r2=0.82, p<0.0001). Because of this, the slope of this linear regression equation may be applied as a tool for tracing environmental processes that affect the surface of the earth. We can do this by directly estimating erosion/sedimentation processes using 7Be or by estimating the input of 10Be in the environment with the aim to evaluate land degradation phenomena.

Determining Air−Water Exchange, Spatial and Temporal Trends of Freely Dissolved PAHs in an Urban Estuary Using Passive Polyethylene Samplers

Passive polyethylene (PE) samplers were deployed at six locations within Narragansett Bay (RI, USA) to determine sources and trends of freely dissolved and gas-phase polycyclic aromatic hydrocarbons (PAHs) from May to November 2006. Freely dissolved aqueous concentrations of PAHs were dominated by fluoranthene, pyrene, and phenanthrene, at concentrations ranging from tens to thousands of pg/L. These were also the dominant PAHs in the gas phase, at hundreds to thousands of pg/m3. All stations mostly followed the same temporal trends, with highest concentrations (up to 7300 pg/L for sum PAHs) during the second of 11 deployments, coinciding with a major rainstorm. Strong correlations of sum PAHs with river flows and wastewater treatment plant discharges highlighted the importance of rainfall in mobilizing PAHs from a combination of runoff and atmospheric washout. PAH concentrations declined through consecutive deployments III to V, which could be explained by an exponential decay due to flushing with cleaner ocean water during tides. The estimated residence time (tres) of the PAH pulse was 24 days, close to an earlier estimate of tres of 26 days for freshwater in the Bay. Air-water exchange gradients indicated net volatilization of most PAHs closest to Providence. Further south in the Bay, gradients had changed to mostly net uptake of the more volatile PAHs, but net volatilization for the less volatile PAHs. Based on characteristic PAH ratios, freely dissolved PAHs at most sites originated from the combustion of fossil fuels; only two sites were at times affected by fuel spill-derived PAHs.

Wet deposition of polychlorinated biphenyls in urban and background areas of the Mid-Atlantic States.

Spatial and temporal trends of polychlorinated biphenyl (PCB) concentrations in precipitation were measured at urban and background sites as part of the New Jersey Atmospheric Deposition Network (NJADN). The volume weighted mean concentration (VWM) of sigmaPCBs (sum of PCBs) based on precipitation measurements at three background sites was in the range of 0.30-0.50 ng/L. Concentrations in precipitation at two urban-industrial sites were on average 7-43 times higher than background concentrations. Wet deposition fluxes of sigmaPCBs at the two urbanized sites were 16 +/- 3.4 and 3.9 +/- 0.72 microg/m2-yr, while the background flux was approximately 0.30 microg/m2-yr. On average, 97% of the total atmospheric washout (WT) of PCBs resulted from particle scavenging. The fraction of atmospheric PCBs on particles was the best predictor of atmospheric washout in both urban (log WT = 0.71 (+/- 0.049) log psi + 4.9 (+/- 0.11); r2 = 0.81) and nonurban areas (log W(T) = 0.77 (+/- 0.083) log psi + 5.6 (+/- 0.16); r2 = 0.64). Wet deposition fluxes of sigmaPCBs are of the same order of magnitude as dry-particle deposition fluxes in all land-use regimes.

Mercury in dated Greenland marine sediments

Twenty marine sediment cores from Greenland were analysed for mercury, and dated by the lead-210 method. In general the cores exhibit a mercury profile with higher mercury concentrations in the upper centimetres of the core. The cores were studied by linear regression of ln Hg vs. age of the sediment for the youngest 100 years. As a rule the mercury decreased with depth in the sediment with various degrees of significance. The increase of the mercury flux during the last 100 years is roughly a doubling. The increase may be of anthropogenic origin as it is restricted to the last 100 years. In four cores the concentration of manganese was found also to increase in the top layers indicating diagenesis. In the other cases the higher concentrations were not accompanied by higher manganese concentrations. The mercury flux to the sediment surface was generally proportional to the Pb-210 flux indicating that the mercury mainly originates from atmospheric washout. But the large variability indicates that other processes also influence the mercury flux to Arctic marine sediments.

Settling Removal Rates of PCBs into the Northwestern Atlantic Derived from 238U−234Th Disequilibria

Surface ocean export fluxes of polychlorinated biphenyls (PCBs) were deduced utilizing 234Th as an indicator of the removal rates of particle-bound species from coastal, continental shelf, and pelagic surface waters. The fraction of the PCB settling flux that reaches the sediments (the ratio of bottom sediment import flux to 234Th-derived surface ocean export flux) decreased with both water column depth and with aqueous solubility of the congeners, presumably as a result of particle decomposition and/or compound desorption. A sharper decrease in 234Th-derived surface ocean fluxes away from the continental source was seen for congeners with increasing chlorination. This suggests that atmospheric washout followed by particle-mediated settling out of the surface ocean are the predominant processes affecting the PCBs, as opposed to atmospheric hydroxyl radical-mediated decomposition. Based on this limited data set, the largest fraction of each PCB is removed into the open ocean, although higher areal fluxes a...

Atmospheric Washout of Polycyclic Aromatic Hydrocarbons in the Southern Chesapeake Bay Region

Vapor washout of selected polycyclic aromatic hydrocarbons (PAHs), determined from discrete atmospheric and integrated precipitation samples collected every two weeks throughout 1991, was observed to be controlled by the Henry's law constant for the compound at the temperature of deposition (5-29 °C). Particle washout was found to be relatively constant for the various PAHs but to vary seasonally, with higher particle scavenging occurring in the spring and summer compared to the fall/winter. Vapor washout coefficients were negatively correlated with rainfall intensity, with stronger dependencies on precipitation rate for high molecular weight PAHs relative to low molecular weight, volatile compounds. This observation indicates that gases of the less volatile PAHs may not achieve equilibrium between air and raindrops during extremely intense precipitation events. Particle washout coefficients for PAHs were positively correlated with rainfall intensity, indicating an increased efficiency for particle scavenging from the atmosphere with precipitation rate.

Atmospheric Washout of Polycyclic Aromatic Hydrocarbons in the Southern Chesapeake Bay Region

Vapor washout of selected polycyclic aromatic hydrocarbons (PAHs), determined from discrete atmospheric and integrated precipitation samples collected every two weeks throughout 1991, was observed to be controlled by the Henry's law constant for the compound at the temperature of deposition (5-29 °C). Particle washout was found to be relatively constant for the various PAHs but to vary seasonally, with higher particle scavenging occurring in the spring and summer compared to the fall/winter. Vapor washout coefficients were negatively correlated with rainfall intensity, with stronger dependencies on precipitation rate for high molecular weight PAHs relative to low molecular weight, volatile compounds. This observation indicates that gases of the less volatile PAHs may not achieve equilibrium between air and raindrops during extremely intense precipitation events. Particle washout coefficients for PAHs were positively correlated with rainfall intensity, indicating an increased efficiency for particle scavenging from the atmosphere with precipitation rate.

An analytical model for air pollutant washout and transport Due to emissions from an elevated source

An analytic treatment of an atmospheric washout and transport model is presented for pollutants released from an elevated source over fiat terrain. The rate of pollutant absorption by falling raindrops is calculated. Results show that the pollutants can be absorbed by the rain drops over distances as large as hundreds of kilometres from the source. The nature of the mean ambient concentration and the vertical profiles of the ambient concentration are also studied. Effects of multiple reflections from the non-absorbing upper and lower boundaries are evident from the nature of the solution.

Foliar retention, transport and leaching of polonium-210 and lead-210

Polonium-210 and lead-210, the long-lived daughter radionuclides of gaseous radon-222, are deposited on plant surfaces under conditions of atmospheric washout. Foliar retention, transport and leaching of these radionuclides in Red Kidney beans were investigated in nutrient culture experiments. Under identical conditions, over 90 per cent of foliar applied radiolead was retained by the plant while only about 30 per cent of polonium was retained. Over a 48-hr period small quantities of polonium were translocated from the treated leaflet to other parts of the plant. By comparison, radiolead was totally immobilized at the site of retention. Leachability of root absorbed radiolead from bean leaves was 20-fold greater than that of polonium. The marked differences in the extent of foliar retention, translocation and leaching of polonium and radiolead could significantly affect the levels of these long-lived radionuclides attained in plants.

Study of atmospheric washout processes by means of radon decay products

A measurement of the departure from radioactive equilibrium between Po/ sup 218/, Pb/sup 214/, and Bi/sup 214/ in a rain cloud or i n fresh rain water can provide an insight into the washout process occurring in the cloud. A convenient and easy method for estimating this departure was developed. The method consists in measuring the rate of change of the resultant activity of Bi/ sup 214/ in the rain sample as a function of time without separating the parent nuclides Po/sup 218/ and Pb/sup 214/. Several rain samples collected at Bombay were analyzed using this method. The results give upper limits for the rate of removal of activity from an air mass by condensation processes on the basis of the simplified continuous washout model discussed.