Deep Convection Leads to Ultrafine Particle Formation and Growth in the Upper Troposphere at Continental Mid-Latitudes
MADELINE COOKE, John Ortega, James Smith, University of California, Irvine
Abstract Number: 129
Working Group: Remote and Regional Atmospheric Aerosol
Abstract
Ultrafine aerosol particles impact climate and weather as a main source of cloud condensation nuclei in the upper troposphere. A wide body of research has demonstrated that the vertical transport of boundary layer pollutants to the upper troposphere during atmospheric convection drives new particle formation in the tropics. Less attention has been paid to continental midlatitudes. During the summertime in the United States, atmospheric convection occurs daily in many regions, particularly in the Southeast. However, the extent to which convection influences upper tropospheric ultrafine particle formation in this region remains unclear. Herein, we report on measurements of ultrafine particles in the upper troposphere during the Deep Convective Clouds and Chemistry (DC3) campaign in May to June of 2012. Across twenty-one flights tracking convective outflow plumes, ultrafine particles were frequently observed. For the majority of flights (~70%), the average number concentrations (N100nm) of particles with diameters between 8 – 100 nm were 10 – 500 cm-3. Several flights exhibited elevated N100nm, with concentrations exceeding 1000 cm-3. Gas-phase measurements were compared for six flights, with three representing elevated N100nm and three, low N100nm, revealing that sulfuric acid and oxidized organic vapors likely contribute to ultrafine particle formation in this region. One particular flight followed a plume and intersected it several times showing that ultrafine particles grew due to photochemical aging at a rate of 2.4 ± 0.1 nm hr-1. Condensation of sulfuric acid can only explain a small fraction of this measured growth. Future measurements are needed to constrain these processes in atmospheric models, particularly of the molecular speciation of both gas-phase precursors and ultrafine composition. Upper tropospheric ultrafine particles in this region may become more important as climate models project increasing frequency and intensity of atmospheric convection in the future.