Volume 16, No. 3, March 2016, Pages 665-673 PDF(528 KB)
Dependence of Daily Aerosol Wet Deposition on Precipitation at Appalachian Mountains Site in the United States
Boston College, Chestnut Hill, Massachusetts, USA
- We examine aerosol wet deposition at mountain site in Eastern United States.
- The wet deposition flux has significant seasonal variation.
- High wet deposition during summer is favored by intense precipitation events.
- Wet deposition is influenced by the origin of air masses and meteorology.
The wet removal of airborne particulates is a significant component of atmospheric deposition in the Eastern United States. This study analyzed the daily wet deposition of major ions at the Canaan Valley site in Appalachian Mountains in Eastern US, for the time interval 2000–2014. The site is part of the Atmospheric Integrated Research Monitoring Network (AIRMoN), and is significantly impacted by acid precipitation, caused largely by anthropogenic sources of SO2 and NOx. Results show that the precipitation rate, R, varies mainly in the interval [0.01–100] mm day–1, and the daily wet deposition flux, F, varies about two orders of magnitude for most ions. The largest daily wet depositions are for SO42– and NO3– with extreme values over 30 mg m–2 day–1. In the case of NH4+, the largest daily wet depositions are over 10 mg m–2 day–1. Seasonal variations are illustrated by contrasting the winter and summer. In general, there are much larger daily wet deposition fluxes in summer than in winter. For SO42– there is more conversion of SO2 to SO42– in the gas phase and in cloud droplets during summer. Similarly, NH4+ has a distinct seasonal variation with a maximum in summer, consistent with larger sources of NH3 during the growth season. NO3– has a maximum concentration in precipitation during winter, and a maximum daily wet deposition flux during summer, especially during the most intense rain events. The Na+ and Cl– ions have the highest wet deposition in winter due to storms that bring air masses from Atlantic. Analysis shows that precipitation events are more frequent and more intense in summer than in winter. For the Canaan Valley, the summer precipitation events are effective in wet removal of aerosols providing episodes with some of the highest rates of acid deposition.
Wet deposition; Air pollution; Aerosol-cloud interactions; Precipitation; Acid rain.