NITRATE AND NON-SEA-SALT SULFATE AEROSOLS OVER MAJOR REGIONS OF THE WORLD OCEAN: CONCENTRATIONS, SOURCES, AND FLUXES.

摘要

Over 1000 bulk aerosol samples were analyzed to determine the geographical and temporal distributions of the concentrations of nitrate and NSS sulfate in the tropospheric boundary layer over major regions of the world ocean. These data were used in combination with several hundred previously published results to estimate the fluxes of nitrate and NSS sulfate to the world ocean.;In many areas, the concentrations of nitrate and NSS sulfate exhibit well-defined seasonal trends. The most dramatic seasonal change occurs over the Arabian Sea where the concentrations during the summer monsoon season are factors of five to six lower than during the remainder of the year. Seasonal variations of factors of two to three are evident for both constituents at Bermuda; Broome, Australia; and Miami, Florida; and for NSS sulfate over the North Pacific Ocean.;The total deposition fluxes of nitrate and NSS sulfate to the world ocean are estimated to be 39 and 73 Tg/yr, respectively. The fluxes to the ocean are far from uniform, ranging over a factor of 20 from one region to another. Much of this variation simply reflects the wide variations in the mean concentrations. However, because wet deposition accounts for an average of 80% of the nitrate flux and 95% of the NSS sulfate flux, geographical variations in total rainfall are also important. Over the relatively pristine areas of the ocean, the nitrate fluxes are compatible with lightning and downmixing from the stratosphere as the major sources of NO(,x). The NSS sulfate fluxes in the same regions are consistent with the homogeneous oxidation of marine background levels of SO(,2).;The area weighted average nitrate and NSS sulfate concentrations over the world ocean are .29 and .67 (mu)g/SCM, respectively. However, the mean concentrations vary substantially (factors of 30 to 50) from one region to another. Mean nitrate and NSS sulfate concentrations range from .09 and .20 (mu)g/SCM, respectively, over the pristine regions of the southern oceans to 3 and 9 (mu)g/SCM, respectively, over the Mediterranean Sea. These substantial geographical variations are primarily a consequence of the regional variations in the quantities derived from continental sources. However, over the relatively pristine areas of the ocean, much of the variation may result from the natural variability of the oceanic and/or atmospheric sources.