Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic on Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions

Gaston, Cassandra J.; Prospero, Joseph M.; Foley, Kristen; Pye, Havala O. T.; Custals, Lillian; Blades, Edmund; Sealy, Peter; Christie, James A.

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect critical biogeochemical cycles, yet their global cycles are poorly understood. To address this issue, we examined trends in 21 years of aerosol measurements made at Ragged Point, Barbados—the easternmost promontory on the island located in the eastern Caribbean Basin. Though the site has historically been used to characterize African dust transport, here we focused on changes in nitrate and non-sea salt (nss) sulfate aerosol from 1990–2011. Nitrate aerosol concentrations are stable at 0.59 ug/m 3 ± 0.04 ug/m 3. Elevated nitrate concentrations in the spring of 2010 as well as during the summer and fall of 2008 are due to transported biomass burning emissions from both northern and southern Africa to our site. In contrast, nss-sulfate decreased 30 % at a rate of 0.02 ug/m 3/yr in the 1990s, which we attribute to air quality policies enacted in the U.S. and Europe. Starting in 2000, sulfate began to increase to pre-1990s levels of 0.90 ug/m 3. We used the Community Multiscale Air Quality (CMAQ) model simulations from the EPA’s Air QUAlity TimE Series (EQUATES) to better understand the changes in nss-sulfate after 2000. The model simulations estimate that increases in anthropogenic emissions, likely from Northern Africa, and increased oxidation efficiency of sulfur dioxide (SO 2) explain the increase in nss-sulfate observed in Barbados. Our results serve as an incentive to better constrain emissions from developing countries and their impact on aerosol burdens in remote regions.

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Gaston, Cassandra J. / Prospero, Joseph M. / Foley, Kristen / et al: Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic on Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions. 2024. Copernicus Publications.

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