Contribution of gaseous and particulate species to droplet solute composition at the Puy de Dôme, France

[摘要] Chemical reactions of dissolved gases in the liquid phase play a key role in atmosphericprocesses both in the formation of secondary atmospheric compounds and their wet removalrate but also in the regulation of the oxidizing capacity of the troposphere. The behavior ofgaseous species and their chemical transformation in clouds are difficult to observeexperimentally given the complex nature of clouds.

During a winter field campaign at the summit of the Puy de Dôme (central France,1465 m a.s.l), we have deployed an experimental set-up to provide a quantification of phasepartitioning of both organic (CH₃COOH, HCOOH, H₂C₂O₄) and inorganic(NH₃, HNO₃, SO₂, HCl) species in clouds.

We found that nitric and hydrochloric acids can be considered close to Henry's lawequilibrium, within analytical uncertainty and instrumental errors. On another hand, forNH₃ and carboxylic acids, dissolution of material from the gas phase is kinetically limited andnever reaches the equilibrium predicted by thermodynamics, resulting in significantsub-saturation of the liquid phase. On the contrary, S^IV is supersaturated in the liquid phase, inaddition to the presence of significant aerosol-derived S^VI transferred through nucleationscavenging.

Upon droplet evaporation, a significant part of most species, including S^IV, tends toefficiently return back into the gas phase. Overall, gas contribution to the droplet soluteconcentration ranges from at least 48.5 to 98% depending on the chemical species. This isparticularly important considering that aerosol scavenging efficiencies are often calculatedassuming a negligible gas-phase contribution to the solute concentration. Our studyemphasizes the need to account for the in-cloud interaction between particles and gases toprovide an adequate modeling of multiphase chemistry systems and its impact on theatmospheric aerosol and gas phases.

[学科分类] 大气科学