Vertical distribution of aerosol particles, water vapor, and insoluble trace gases in convectively mixed air

Abstract

Vertical distributions of submicrometer size aerosol particles, water vapor, and the insoluble gases (O3, CO, and NOy) were determined from measurements made during 12 aircraft flights conducted in June 1987 near Columbus, Ohio. Measurements extended from the surface to 290 mbar (∼9.5 km) and were made primarily in the vicinity of convective storms. The mixing ratio of aerosol particles decreased strongly with altitude, from an average value of 1800 scm−3 (SCM, standard centimeter) (at 20°C, 1 atm) near the surface to a value in the upper troposphere (30 scm−3, above 300 mbar) that was, on average, less than 2% of the near‐surface mixing ratio. This decrease was similar to that exhibited by water vapor. CO and NOy, in contrast, were more uniformly distributed. Average upper tropospheric mixing ratios were 128 and 0.8 ppb, 51 and 35%, respectively, of boundary layer values. Compact plumelike features were observed at high altitude in which concentrations of boundary layer constituents increased by 50% or more over a distance of several kilometers. These features are attributed to boundary layer air that had been transported upward in convective storms. Such boundary layer air encountered aloft could contain higher mixing ratios of water vapor and aerosol particles than found in adjacent regions, but on an absolute basis these soluble substances were always severely depleted relative to the insoluble gases, CO and NOy. We ascribe the qualitative difference between the vertical distributions of soluble and insoluble substances as being due to in‐cloud processes occurring during upward transport. The upward transport of soluble material is limited by dissolution in cloud water and subsequent conversion of cloud water to downward moving precipitation, whereas insoluble pollutants are not affected by this process.