Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Dadashazar, Hossein, Alipanah, Majid, Hilario, Miguel Ricardo A., Crosbie, Ewan, Kirschler, Simon, Liu, Hongyu, Moore, Richard H., Peters, Andrew J., Scarino, Amy Jo, Shook, Michael, Thornhill, K. Lee, Voigt, Christiane, Wang, Hailong, Winstead, Edward, Zhang, Bo, Ziemba, Luke, Sorooshian, Armin
• Format: Text
• Language: English
• Published: 2021
• Subjects: Article; Aerosol Robotic Network; North Atlantic
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8609468/; http://www.ncbi.nlm.nih.gov/pubmed/34819950; https://doi.org/10.5194/acp-21-16121-2021

North American pollution outflow is ubiquitous over the western North Atlantic Ocean, especially in winter, making this location a suitable natural laboratory for investigating the impact of precipitation on aerosol particles along air mass trajectories. We take advantage of observational data collected at Bermuda to seasonally assess the sensitivity of aerosol mass concentrations and volume size distributions to accumulated precipitation along trajectories (APT). The mass concentration of particulate matter with aerodynamic diameter less than 2.5 μm normalized by the enhancement of carbon monoxide above background (PM(2.5)/ΔCO) at Bermuda was used to estimate the degree of aerosol loss during transport to Bermuda. Results for December–February (DJF) show that most trajectories come from North America and have the highest APTs, resulting in a significant reduction (by 53 %) in PM(2.5)/ΔCO under high-APT conditions (> 13.5 mm) relative to low-APT conditions (< 0.9 mm). Moreover, PM(2.5)/ΔCO was most sensitive to increases in APT up to 5 mm (−0.044 μg m(−3) ppbv(−1) mm(−1)) and less sensitive to increases in APT over 5 mm. While anthropogenic PM(2.5) constituents (e.g., black carbon, sulfate, organic carbon) decrease with high APT, sea salt, in contrast, was comparable between high- and low-APT conditions owing to enhanced local wind and sea salt emissions in high-APT conditions. The greater sensitivity of the fine-mode volume concentrations (versus coarse mode) to wet scavenging is evident from AErosol RObotic NETwork (AERONET) volume size distribution data. A combination of GEOS-Chem model simulations of the (210)Pb submicron aerosol tracer and its gaseous precursor (222)Rn reveals that (i) surface aerosol particles at Bermuda are most impacted by wet scavenging in winter and spring (due to large-scale precipitation) with a maximum in March, whereas convective scavenging plays a substantial role in summer; and (ii) North American (222)Rn tracer emissions contribute most to surface (210)Pb concentrations at ...