Over the past decade it has become apparent that the atmosphere is a significant pathway for the transport of many natural and pollutant materials from the continents to the ocean. The atmospheric input of many of these species can have an impact (either positive or negative) on biological processes in the sea and on marine chemical cycling. For example, there is now evidence that the atmosphere may be an important transport path for such essential nutrients as iron and nitrogen in some regions. In this report we assess current data in this area, develop global scale estimates of the atmospheric fluxes of trace elements, mineral aerosol, nitrogen species, and synthetic organic compounds to the ocean; and compare the atmospheric input rates of these substances to their input via rivers. Trace elements considered were Pb, Cd, Zn, Cu, Ni, As, Hg, Sn, Al, Fe, Si, and P. Oxidized and reduced forms of nitrogen were considered, including nitrate and ammonium ions and the gaseous species NO, NO2, HNO3, and NH3. Synthetic organic compounds considered included polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs), DDTs, chlordane, dieldrin, and hexachlorobenzenes (HCBs). Making this assessment was difficult because there are very few actual measurements of deposition rates of these substances to the ocean. However, there are considerably more data on the atmospheric concentrations of these species in aerosol and gaseous form. Mean concentration data for 10° × 10° ocean areas were determined from the available concentration data or from extrapolation of these data into other regions. These concentration distributions were then combined with appropriate exchange coefficients and precipitation fields to obtain the global wet and dry deposition fluxes. Careful consideration was given to atmospheric transport processes as well as to removal mechanisms and the physical and physicochemical properties of aerosols and gases. Only annual values were calculated. On a global scale atmospheric inputs are generally equal to or greater than riverine inputs, and for most species atmospheric input to the ocean is significantly greater in the northern hemisphere than in the southern hemisphere. For dissolved trace metals in seawater, global atmospheric input dominates riverine input for Pb, Cd, and Zn, and the two transport paths are roughly equal for Cu, Ni, As, and Fe. Fluxes and basin‐wide deposition of trace metals are generally a factor of 5‐10 higher in the North Atlantic and North Pacific regions than in the South Atlantic and South Pacific. Global input of oxidized and reduced nitrogen species are roughly equal to each other, although the major fraction of oxidized nitrogen enters the ocean in the northern hemisphere, primarily as a result of pollution sources. Reduced nitrogen species are much more uniformly distributed, suggesting that the ocean itself may be a significant source. The global atmospheric input of such synthetic organic species as HCH,PCBs, DDT, and HCB completely dominates their input via rivers.

Abstract. Estimates of atmospheric dust deposition to five Asian/Pacific regions indicate that -800 Tg of Chinese desert dust is injected into the atmosphere annually; about 30% of this is redeposited onto the deserts, 20% is transported over regional scales, primarily within continental China. The remaining 50% of the dust is subject to long-range transport to the Pacific Ocean and beyond. Elemental tracers based on several dustderived elements (A1, Fe, Mg, and Sc) reveal high-frequency variability in the contributions of the western desert sources versus northern high-dust and low-dust desert sources to eolian deposits from the center of the Loess Plateau. Comparisons of the patterns uncovered with climate signals from the remote North Atlantic region for the last glaciation show that shifts in source areas of Asian dust were synchronous with large-scale variations in atmospheric circulation. spring of 1994 were analyzed directly using proton-induced X ray emission (PIXE). The PIXE analyses were performed using the 2.5 MeV protons with a 50 nA beam current produced by the 2 x 1.7 MV tandem accelerator at Beijing Normal University. Using these procedures, we were able to determine the concentrations of 17 elements, but in this paper we only consider the data for Al, Fe, Mg, and Sc. The concentrations of these four elements also were determined by PIXE in eight aliquots of a standard reference material from National Bureau of Chemical Exploration Analysis, China [GSS, 1984]. The results showed that the precision (<10%) and accuracy (<20%) were satisfactory. 3.Results and Discussion Atmospheric Emission of Chinese Desert DustAs a first approximation, all of the Chinese desert dust produced is assumed to deposit in regions A, B, C, D, and E (i.e., deposition equal to production, Figure 1). The total dust deposited is calculated as the sum of the dry plus the wet deposition averaged over each region (Tables 1 and 2 28,041

[1] Simulations of Asian dust emissions over the past 43 years are presented based on a size-dependent soil dust emission and transport model (NARCM) along with supporting data from a network of surface stations. The deserts in Mongolia and in western and northern China (mainly the Taklimakan and Badain Juran, respectively) contribute $70% of the total dust emissions; non-Chinese sources account for $40% of this. Several areas, especially the Onqin Daga sandy land, Horqin sandy land, and Mu Us Desert, have increased in dust emissions over the past 20 years, but efforts to reduce desertification in these areas may have little effect on Asian dust emission amount because these are not key sources. The model simulations indicate that meteorology and climate have had a greater influence on the Asian dust emissions and associated Asian dust storm occurrences than desertification.

Abstract. The cycling of inorganic bromine in the marine boundary layer (mbl) has received increased attention in recent years. Bromide, a constituent of sea water, is injected into the atmosphere in association with sea-salt aerosol by breaking waves on the ocean surface. Measurements reveal that supermicrometer sea-salt aerosol is substantially depleted in bromine (often exceeding 50%) relative to conservative tracers, whereas marine submicrometer aerosol is often enriched in bromine. Model calculations, laboratory studies, and field observations strongly suggest that the supermicrometer depletions reflect the chemical transformation of particulate bromide to reactive inorganic gases that influence the processing of ozone and other important constituents of marine air. Mechanisms for the submicrometer enrichments are not well understood. Currently available techniques cannot reliably quantify many Br-containing compounds at ambient concentrations and, consequently, our understanding of inorganic Br cycling over the oceans and its global significance are uncertain. To provide a more coherCorrespondence to: R. Sander (sander@mpch-mainz.mpg.de) ent framework for future research, we have reviewed measurements in marine aerosol, the gas phase, and in rain. We also summarize sources and sinks, as well as model and laboratory studies of chemical transformations. The focus is on inorganic bromine over the open oceans outside the polar regions. The generation of sea-salt aerosol at the ocean surface is the major tropospheric source producing about 6.2 Tg/a of bromide. The transport of Br from continents (as mineral aerosol, and as products from biomass-burning and fossil-fuel combustion) can be of local importance. Transport of degradation products of long-lived Br-containing compounds from the stratosphere and other sources contribute lesser amounts. Available evidence suggests that, following aerosol acidification, sea-salt bromide reacts to form Br 2 and BrCl that volatilize to the gas phase and photolyze in daylight to produce atomic Br and Cl. Subsequent transformations can destroy tropospheric ozone, oxidize dimethylsulfide (DMS) and hydrocarbons in the gas phase and S(IV) in aerosol solutions, and thereby potentially influence climate. Inorganic bromine in the mbl gas phase during daytime are consistent with expectations based on photochemistry. We expect that the importance of inorganic Br cycling will vary in the future as a function of both increasing acidification of the atmosphere (through anthropogenic emissions) and climate changes. The latter affects bromine cycling via meteorological factors including global wind fields (and the associated production of sea-salt aerosol), temperature, and relative humidity.

A large international field experiment and use of transport modeling has yielded physical, chemical, and radiative properties of the abundant aerosols originating from Asia.

Trends in Chinese global radiation, direct horizontal radiation, diffuse radiation, clearness index, diffuse fraction and percentage of possible sunshine duration for the period 1961–2000 were evaluated based on data for daily surface solar radiation and monthly sunshine duration. Annual means for all six variables were calculated for each station and for China as a whole. Linear regression analysis was used to characterize long‐term annual trends in these variables. Over the latter half of the 20th century, there have been significant decreases in global radiation (−4.5 W/m2 per decade), direct radiation (−6.6 W/m2 per decade), clearness index (−1.1% per decade), and the percentage of possible sunshine duration (−1.28% per decade), but diffuse fraction has increased (1.73% per decade). Although there is some evidence that conditions have improved in the last decade, the consistent spatial and temporal variations of these variables support the theory that increased aerosol loadings were at least partially responsible for the observed decreases in global radiation and direct radiation, the clearness index, and the monthly percentage of possible sunshine duration over much of China.

Aerosol particle samples collected from Asia and the North Pacific were analyzed to investigate the relationships among atmospheric sea salt, mineral aerosol, biogenic emissions (methanesulfonate (MSA)), and several anthropogenic substances (sulfate, nitrate, and various trace elements). These studies specifically focused on the sources for aerosol SO• and on the long-range transport of continental materials to the North Pacific. Ground-based aerosol sampling was conducted at four coastal-continental sites: Hong Kong, Taiwan, Okinawa, and Cheju; and at three remote Pacific islands, Shemya, Midway, and Oahu. Non-sea-salt (riss) SO• and MSA were uncorrelated at the East Asian sites presumably because pollution sources overwhelm the biogenic emissions of nss SO•. At the coastal-continental sites, marine biogenic emissions accounted for only 10 to <5% of the total nss SOj. In contrast, over the ocean the concentrations of riss SO2 and MSA were correlated (Midway r -0.70; Oahu r = 0.59), and higher percentages of biogenic riss SO• occurred, 55 and 70% at Oahu and Midway, respectively. The concentrations of riss SO• and NO•-were correlated at Cheju, Hong Kong, Taiwan, Okinawa, Midway, and Oahu, indicating some similarities in their sources and the processes governing their transport; however, differences in the riss SO•/NO•-ratios among sites suggest regional differences in the pollution component of the aerosol. At Shemya the concentrations of MSA during the summer (100 ng m -3 or more) are about 2 orders of magnitude higher than those in winter. The dimethylsulfide-derived fraction of the riss SO2 is highest in the summer when the monthly median riss SO2/MSA ratios range from 2.7 to 4.5, i.e., comparable to the ratios observed over Antarctica and other high-latitude locations. However, the monthly median riss SO•/MSA ratios increase, reaching 50 to 200 in the winter as productivity nearly ceases, and the biogenic fraction of nss SO• at Shemya decreases dramatically; this suggests a strong seasonal pollution component to the sulfate aerosol. The meteorological conditions favoring the long-range transport of Asian dust to the North Pacific also lead to transport of anthropogenic materials. At Oahu the correlation between NO• and A1 (dust) was highly significant (r = 0.75; p < 0.001), while the correlations between nitrate and A1 at the continental sites were low. These differences indicate that the composition of the air sampled at the coastalcontinental stations may be quite different from the air transported to the remote ocean. This phenomenon also appeared to affect the relationship between riss SO• and antimony. The correlations between riss SO• and Sb were weak at the Asian sites but strong at the open ocean sites where the riss SO•/Sb ratios were higher than those over the continent. Introduction The rapid industrial development in Asia is responsible for the high and increasing concentrations of a variety of air pollutants in the region. While the atmosphere over the remote North Pacific Ocean is thought to be ...

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