Temporal variations, transport, and regional impacts of atmospheric aerosol and acid gases close to an oil and gas trading hub

Direct quantification of changes in pH within single levitated microdroplets and the kinetics of nitrate and chloride depletion

“…The kinetics of depletion have been theoretically derived by Chen et al 38 In that analysis, it was assumed that the depleting species (HNO 3 or HCl) instantly formed at the air/water interface and then the rate of evaporation from a diffusion-limited mass-transfer model was calculated. 42 The characteristic time, t*, and an associated constant, k, are given in eqn (7) and (8),…”

“…7 3 Depletion of chloride and nitrate in aqueous droplets has been observed in various field and laboratory studies, and occurs to a great enough extent to impact hygroscopicity and source apportionment considerations. 2,[8][9][10][11] However, several fundamental aspects of the depletion process remain unclear. Since HNO3 or HCl must form at or diffuse to the surface in order to partition into the gas phase, one might assume that depletion would be greatest for smaller aqueous droplets with higher surface area to volume ratios.…”

“…For field studies, coalescence and agglutination of droplets add yet another degree of complexity to tracking chloride or nitrate depletion. 8 For laboratory-generated microdroplets and aerosols that are deposited for days before analysis, the volatilization of different components or the action of dehydration could convolute the analysis of these processes.…”