Aerosol composition and size versus altitude measured from the C-130 during ACE-Asia



[1] During the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) intensive experiment in the spring of 2001 we used a total aerosol sampler (TAS) and a micro-orifice impactor (MOI) to collect dust and pollution aerosols for ion chromatographic analysis. An aerodynamic particle sizer (APS) was used to estimate the total coarse-mode volume. We conducted postexperiment passing efficiency measurements on the APS, the MOI, and their delivery tubing to constrain the inevitable (and sometimes large) artifacts associated with sampling supermicron particles from an aircraft. We have combined TAS and corrected MOI data to estimate ambient coarse and fine sulfate, ammonium, nitrate, calcium, sodium, chloride, potassium, magnesium, and oxalate. We found significant differences between aerosol composition in the free troposphere (FT) and boundary layer (BL). The molar ratio of nitrate to soluble calcium averaged 1.8 in the BL, but only 0.2 in the FT. Nitrate and calcium frequently had identical coarse size distributions, while sulfate and ammonium often had identical fine distributions. Dust clearly directs NOy toward coarse-mode nitrate. Sulfate in the FT was closest to ammonium bisulfate (half neutralized), while non-sea-salt sulfate (NSS) in the BL was usually completely neutralized to ammonium sulfate. In the presence of dust, up to half the NSS was found in the coarse mode, probably the result of SO2 uptake by CaCO3 in the dust. Soluble calcium averaged 5–8% of the coarse dust mass inferred from the APS. BL aerosol chemistry was seldom a good indicator of ionic composition in the FT.