Observational Evidence for the Convective Transport of Dust Over the Central United States

Bulk aerosol composition and aerosol volume size distributions measured aboard the DC-8 aircraft during DC3 (Deep Convective Clouds and Chemistry Experiment) in May/June 2012 were used to investigate the transport of mineral dust through nine storms encountered over Colorado and Oklahoma. Measurements made at low altitudes (< 5 km ASL) in the storm inflow region were compared to those made in storm cirrus anvils (altitude > 9 km ASL). Storm mean outflow calcium mass concentrations and total coarse (1 micron < diameter < 5 micron) aerosol volume were comparable to mean inflow values, suggesting these particles are not efficiently removed by warm or cold cloud scavenging. A positive relationship between calcium, aerosol volume, ice water content (IWC), and large (diameter > 50 micron) ice particle number concentrations was not evident thus the influence of ice shatter on these measurements was assumed small. Mean inflow aerosol number concentrations calculated over a diameter range (0.5 micron < diameter < 5.0 micron) relevant for potential ice nuclei (PIN) were ~10-200 times higher than ice particle concentrations for all storms. Ratios of predicted interstitial PIN (calculated as the difference between inflow PIN and ice particle concentrations) and inflow PIN were consistent with those calculated for calcium and aerosol volume and indicated that, on average, less than 10% of the ingested PIN were activated as ice nuclei during anvil formation.