Modeling studies of atmospheric aerosols in remote marine regions.

摘要

Global oceans are a predominant natural source of atmospheric aerosols, which play an important role in both atmospheric chemistry and climate. The role of aerosols is in turn dependent upon the complex particle properties, which are closely coupled with ambient gas concentrations and remain poorly quantified. In this work, state-of-the-art computer models are applied to study the chemical composition and optical properties of aerosols in remote marine regions. Studies are performed using extensive data gathered on ship, aircraft, and land platforms during two recent international field experiments: (i) the First Aerosol Characterization Experiment (ACE 1) conducted over the Southern Ocean during 1995 and (ii) the European Arctic Aerosol Study (EAAS) conducted on the coast of northern Finland during 1997. Field data used include size-resolved aerosol ionic composition (sodium, chloride, magnesium, calcium, potassium, sulfate, methanesulfonate, nitrate, and ammonium), ambient gas concentrations (ammonia, nitric acid, hydrochloric acid, formic acid, and acetic acid), meteorological variables, and point and profile measurements of aerosol scattering coefficient and optical depth spectra spanning the visible wavelengths. The EQUISOLV II gas-aerosol thermodynamic equilibrium model is applied to study aerosol composition and a Mie scattering model is further applied to study aerosol optical properties. Results of aerosol composition studies during ACE 1 and EAAS indicate that: (i) all submicron aerosols are in equilibrium with all inorganic gases; (ii) supermicron marine aerosols are undersaturated with nitric acid; (iii) the known thermodynamics of formic and acetic acids cannot explain their observed gas-aerosol partitioning; (iv) the pH of submicron marine aerosols is 0–2, controlled by the amount of secondary sulfate present; and (v) the equilibrium pH of supermicron marine aerosols is 2–5, controlled by the effect of relative humidity on the gas-aerosol partitioning of hydrochloric acid. Results of aerosol optical property studies during ACE 1 indicate that: (i) optical properties are dominated by sea spray; (ii) total scattering can be adequately modeled when dried sea spray is assumed to be spherical but modeling backscattering requires a parameterization for particle nonsphericity; and (iii) free tropospheric and stratospheric aerosols may contribute significantly to mid-visible aerosol optical depth in remote marine regions.