Estimated Timescales for Wet Deposition of Organic Compounds as a Function of Henry’s Law Constants
CHENYANG BI, Gabriel Isaacman-VanWertz,
Virginia Tech Abstract Number: 162
Working Group: Aerosol Chemistry
AbstractAtmospheric organic compounds may deposit to Earth’s surfaces via dry deposition, driven by gravity and/or concentration gradients, and wet deposition, driven by the washouts of compounds in rain or snow. Their removal by deposition has downstream impacts on concentrations of secondary organic aerosol (SOA) by preempting their atmospheric oxidation, which can form SOA. The impact of deposition processes can consequently be considered as competition between rates of oxidation and deposition, but timescales for deposition are not well constrained. While dry deposition timescale has been estimated and experimentally validated in the past, understanding of wet deposition is still very limited. In this work, we estimate the wet deposition timescale of gas-phase organic compounds in the atmosphere as a function of Henry’s law constants, H
eff. Real-world precipitation frequency and size distributions at three sites provide a globally distributed estimate of this timescale. The wet deposition timescale decreased significantly with the increase of H
eff and became constant for compounds with H
eff >10
5 M/atm. We estimate that the median wet deposition timescale for compounds with H
eff >10
5 M/atm is approximately 5 hours during a continuous rain event for all three sites. However, median estimated timescales ranged from 80 to 200 hours, depending on location, and depend more on the frequency and duration of precipitation events rather than their intensity or size characteristics. We present to estimate timescales at any location for which basic precipitation information is available, use this approach to examine potential global distributions of timescales for wet deposition, and discuss them in the context of competition with other loss processes.