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

• Published in: Atmospheric chemistry and physics Vol. 24; no. 13; pp. 8049 - 8066
• Main Authors: Gaston, Cassandra J, Prospero, Joseph M, Foley, Kristen, Pye, Havala O. T, Custals, Lillian, Blades, Edmund, Sealy, Peter, Christie, James A
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 16.07.2024; Copernicus Publications
• Subjects: Aerosol concentrations; Aerosol effects; Aerosol measurements; Aerosols; Air; Air pollution; Air quality; Air quality measurements; Air quality models; Analysis; Anthropogenic factors; Atmospheric chemistry; Atmospheric particulates; Biogeochemical cycle; Biogeochemical cycles; Biomass burning; Developing countries; Dust; Dust transport; Economic growth; Emissions; Environmental aspects; Environmental policy; Human influences; Hydrologic cycle; Hydrological cycle; Laboratories; LDCs; Nitrates; Observatories; Outdoor air quality; Policies; Prescribed fire; Radiative forcing; Sulfate aerosols; Sulfates; Time series; Trends; Barbados; Africa; United States > US; North America; Europe; India
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-24-8049-2024

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect biogeochemical cycles, yet their global cycles are poorly understood. Here, 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 aerosols from 1990–2011. Nitrate aerosol concentrations averaged over the entire period were stable at 0.59 µg m−3 ± 0.04 µg m−3, except for elevated nitrate concentrations in the spring of 2010 and during the summer and fall of 2008 due to the transport of biomass burning emissions from both northern and southern Africa to our site. In contrast, from 1990 to 2000, nss-sulfate decreased 30 % at a rate of 0.023 µg m−3 yr−1, a trend which we attribute to air quality policies enacted in the United States (US) and Europe. From 2000–2011, sulfate gradually increased at a rate of 0.021 µg m−3 yr−1 to pre-1990s levels of 0.90 µg 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 from Africa explain the increase in nss-sulfate observed in Barbados. Our results highlight the need to better constrain emissions from developing countries and to assess their impact on aerosol burdens in remote source regions.