Abstracts of Other Papers 2075

(S~REX)~.~nningin 1981,wctlriylPlnpla~~~r~~oolkctedinaSEARW: network of seven island stations in the North Pacific Since early 1983, weekly samples have been collected in a similar SEAREX network of seven island stations in the South Pacific. In addition, samples have been collected aboard ships during seven separate research cruises.

This extensive data set reveals a number of sign&ant trends in the areai dist~bution of the notations of particulate nitrate and NSS sulfate and in the tempoml variability of these conccnlrations. Over a vast region of the North Pacific. signi!Icant quantities of these two constituents appear to be derived from Asia. It has previously been shown that a massive transport of A&n Dust occurs over this region from February to June of each year. During this same period mean NSS sulfate concentrations range from 0.49 to 0.78 pg m _ 3 (STP) and mean nitrate concentrations range from 0.3 1 to 0.40 pg m -‘. In contrast, from August to January the mean NSS sulfate concentrations are nearly a factor of two lower than during the high dust season, 0.28431 w m-‘; the mean nitrate concentrations arc also somewhat lower, 0.25432 pg mmJ.

Continental sources ckarfy have a major impact on the concentrations of aerosof nitmte and NSS sulfate in the eastern Pacific off the coast of southwest United States and Central America; mean nitrate concentrations in these areas range from 0.7 to 2 erg m- 3 and NSS sulfate from 2 to 9 pg m-‘. There appear to be major sources of sulfate precursors in southern Peru and northern Chilt; concentrations of NSS sulfate in areas off the northwest coast of South America can exceed 20 ~8 m-‘.

The equatorial Pacific and the tropical and sub-tropical areas of the South Pacific constitute a major region in which natural marine and/or global atmospheric sources appear to supply the majority of the nitrate and NSS sulfate. ~roughout this region mean nitrate inactions are about 0.09 pg m- ‘; mean NSS sulfate concentrations vary from 0.15 to 0.50 ~cg m -3. Estimated fluxes of nitrate to the equatorial Pacific and tropical South Pacific (390 and 14Opg mm2 per day, respectively) are consistent with the estimated production rate of NO, from lightning and from the stratosphere. The fluxes of NSS sulfate (1300 and 610 pg mW2 per day) are consislent with recent estimates of the fluxes of dimethyl sulfide from the ocean.

EXCHANGE OF TRACE ELEMENTS BETWEEN THE ATMOSPHERE AND THE TROPICAL PACIFIC OCEAN

R. ARIMOTO, R. A. DUCE and B. J. RAY Center for Atmospheric Chemistry Oceanography, University of Rhode Island, Kingston, RI 02881, U.S.A.

The rates of trace element air-sea exchange are estimated from samples of precipitation and dry deposition collected during the SEAREX (Sea/Air Exchange) studies at Encwetak Atoll and American Samoa in the tropical North and South Pacific, respectively. In samples from Enewetak the con~ntrations of Al, SC, Mn, Fe, Co and Tb are dominated by weathered crustal material which originates in the deserts of Asia. During the spring and early summer, the atmospheric deposition of these elements is higher than in the remainder of the year due to the scasonality of dust storms in Asia and changes in the long-range transport pathways. The atmospheric deposition of the crustally derived elements is dominated by wet removal, and the present deposition rates are similar lo the rates ofaccumulation in sediments, suggesting thal the air-sea exchange of particles is tied to the marine sedimentary cycle. The fluxes ofcrustally derived elements at Samoa are lower than those in the tropical North Pacific owing to the weaker sources ofcrustal material for the atmosphere of the southern hemispheres.

The concentrations of Pb, Zn, 0.1 Se and Cd in deposition samples from both sites are higher than those expected from mineral aerosol or the injection of bulk seawater into theatmosphere. Theseenrichments may be due to natural processes, but anthropogenic emissions clearly are responsible for the enrichments of Pb, for example. The deposition of the enriched ekments al Samoa generally is lower than at Enewetak, and this may reflect the lower anthropogcnic emissions in the sounhem hemisphere. Estimates of the atmospheric deposition due to recycled sea spray are made from the observed traceelemmt enrichments in sea salt aerosol particles and the measured deposition of Na The recycled component of the gross deposition varies markedly between samples and often amounts to more than 50% of the total input. Estimated fluxes of ckments such as Cu and Zn from the atmosphere to the surface waters of the tropical N Pacific are similar to the estimated inputs due to vertical mixing in the ocean, but the net deposition of Pb clearly exceeds the input from upwclling. At Enewctak the current net atmospheric deposition of certain enriched elements is greater than or equal to their marine sedimentation rates, which is another indication that air-sea exchange processes affect the chemistry of trace elements in the ocean.

ATMOSPHERIC CYCLING OF MERCURY OVER THE PACIFIC OCEAN

WILLIAM F. FITZGERALD, JONATHAN P. KIM, GARY A. GILL and ALAN D. HEWITT Marine Sciences Department and Marine %ences Institute, Tbe University of Connecticut, Groton,

Connecticut 06340, U.S.A.

The atmospheric cycle of Hg over the oceans is being investigated as part of a more general effort concerned with the global cycling of Hg and its behavior and fate in the marine ~vi~n~t. Much of this work has been

2076 Abstracts of Other Papers

conducted with the SEAREX (Sea-Air Exchange) Programand many new data for Hg have been acquired in remote tradewind regions of the Pacific Ocean (e.g. at Enewetak Atoll and American Samoa), in the NW Atlantic Ocean, in the nearshore environs of Long Island Sound and the Peru Upwelling, and most recently in the S Pacific westerlies regime at New Zealand. This oceanic coverage has been broad and includes measurements of Hg in the atmosphere, in precipitation and in seawater from both hemispheres.

These studies of the air-sea exchange of Hg and anciRary investigations concerned with Hg sources and source strengths are yielding unique. critically needed geochemical information which is well constrained and amenabk tomodelling. M&t of ihe Hg in the atmosphere over the oceans is in the vapor phase. At Enewetak Atoll. for exam&. the averaxe total xaseous Ha concentration (TGM) was 1.7 f 0.5 rut/SCM while the particulate com.ponent was a&t lG times s&lkr (0.62 pg/SCM). Similar atmosphe& levels of TGM were found over other N Hemisphere open ocean regions while smalkrconcentrations ( _ 1.0 ng/SCM) were observed for comparable Pacific Ocean regions of the S Hemisphere. Ekvated TGM concentrations in the atmosphere, suggestive of Hg evasion from the sea surface, were found over the central equatorial Pacific Ocean and at American Samoa. Substantial increases in TGM and particulate Hg concentrations occur in coastal regions such as Long Island Sound and organic gaseous forms of Hg as determined by Ag/Au partitioningareevident. The hemisphereand interhemisphericatmospheric Hgdistribution patterns indicate that (1) continental sources predominate over oceanic sources, and (2) continental emissions of Hg are primarily gaseous and include elemental Hg, organo-Hg species and. perhaps, other volatile inorganic Hg compounds. Mercury transfer and exchange with the oceans is analogous to a trace gas whose primary sources are continental and include natural and anthropogenic processes. Geochcmical mass balanceanalysis yields a tropospheric residence time for TGM that is of the order of one year and indicates that anthropogenic fluxes of Hg through the atmosphere are comparable to natural fluxes.

SEVERAL STUDIES RELATED TO ACID PRECIPITATION IN JAPAN

T. OKITA

National Institute for Environmental Studies, Yatabe-machi, Ibaraki-ken 305. Japan

S. OHTA

Department of Environmental Engineering, Hokkaido University, Sapporo 060, Japan

T. KOMEIJI

Tokyo Metropolitan Research Institute for Environmental Protection, Toyo-cho, Koto-ku, Tokyo 135, Japan

and

H. HARA

National Institute of Public Health, Shirokane-dai, Minato-ku, Tokyo 108. Japan

Several studies have been made in relation to acid precipitation. They are the measurement and modeling of acidic cloud, the comparison of deposition ofacidicand alkaline species in 1962-1963 and 1980-1981 in the Tokyo area, the measurement of vertical distributions of SOi- and other species over the Kanto area, a summary of volcanic emission of SO,, and the laboratory studies of the oxidation of sulfite by O2 in aqueous phase such as precipitation water.

SPATIAL AND HISTORICAL TRENDS IN ACIDIC DEPOSITION: A GRAPHICAL INTERSITE COMPARISON

ELMAR R. ALTWICKER

Department of Chemical Engineering and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, New York 12810, U.S.A.

In this contribution a graphical approach is preaented to the analysis of intersite comparison with respect to the composition of precipitation. The composition is expressed as the (base cations), i.e. NH,, Ca, Mg, K and N&and the Z(acid anions), i.e. SOa, NOa and Cl. Non-acidic site-s are those that receive precipitation whose composition places them near or above a 1: I line on a plot of Z(base cations) vs Z(acid anions). The composition ofacidic sites @H < 4.5) are such that they will fall near or below a 1:2 (or 1: 3) line of the same plot. If a site is assumed to be non-acidic it could become acidic by a decrease in I: (basecations), an increase in X(acid anions) or a combination of such changes.