Influence of vertical transport on free tropospheric aerosols over the central USA in springtime

Abstract

Measurements of the atmospheric aerosol chemical composition during the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) indicate substantial vertical transport of boundary layer aerosol to the free troposphere over the south‐central United States during springtime. Mixing ratios of water‐soluble aerosol Ca 2+ at 6–12 km altitude exhibited a median mixing ratio of 20 pptv, with 15% of the measurements ≥ 100 pptv and a maximum of 1235 pptv. In air parcels with enhanced Ca 2+ , the ratios K + /Ca 2+ , Mg 2+ /Ca 2+ , and Na + /Ca 2+ in the bulk aerosol were distinctly characteristic of those in limestone and/or cement. Significantly enhanced mixing ratios of aerosol SO 4 2− , NO 3 − , and NH 4 + were also concomitant with the elevated Ca 2+ , suggesting transport of both crustal and anthropogenic aerosols to the upper troposphere. The mass concentration of water‐soluble aerosol material was in the range 0.1–6 µg m −3 STP, and estimated crustal dust levels were 7–160 µg m −3 STP.