Impacts of Precipitation Events on Concentrations of Oxygenated Gas- and Particle-Phase Compounds Observed in the Amazon

Removal of gases and particles by precipitation (wet
deposition)
is a critical process that significantly influences the transport
and chemical transformation of atmospheric compounds. However, there
are few studies that directly measure or constrain the rates of this
process under real-world conditions. This work quantifies the net
change in ambient concentrations during precipitation events (removal
rates) of gas- and particle-phase organic compounds at a surface site
near Manaus, Brazil, during the GoAmazon2014/5 campaign. Removal rates
of identified and unknown compounds that have been previously classified
into source-based clusters are measured during rain events and categorized
based on estimated properties of compounds and clusters. Highly oxygenated
gases, such as isoprene oxidation products, are removed during precipitation
events with a median removal rate of 0.09 h–1 and
the fastest analyte is removed at a rate of 0.22 h–1. Removal rates of particle-phase compounds are observed at roughly
this median rate, while less soluble gases, such as terpenes, exhibit
low removal rates. These results are roughly in agreement with prior
theoretical estimates of wet deposition rates for comparable compounds,
providing an empirical point of comparison while noting that our metric
reflects the net influence of precipitation events rather than wet
deposition alone.