Comprehensive Analysis of Particle Growth Rates at an Agricultural Site

ELEANOR BROWNE, Jennifer Berry, Bri Dobson, Daniel Katz, University of Colorado Boulder

     Abstract Number: 515
     Working Group: Aerosols, Clouds and Climate

Abstract
Elucidating the processes by which particles grow to sizes at which they can act as cloud condensation nuclei (CCN) is critical for constraining the global energy budget. However, the understanding of the key processes governing particle growth remains weak particularly the relative roles of condensational growth versus condensed-phase chemistry. Growth rates (GR) have typically been calculated for nucleation mode particles; however, as particles typically need to grow to 50-100 nm in diameter to act as CCN, it is necessary to understand how GR varies with particle diameter. Here, we analyze approximately six years of particle size distribution data in combination with meteorological data to investigate the processes controlling particle growth at the Department of Energy Atmospheric Radiation Measurement Southern Great Plains site. We use an automated algorithm to find regional aerosol growth events (>2 h of monotonic growth) for starting particle sizes ranging from ~20 nm to ~450 nm and calculate the growth rates. Across all starting diameters, growth rates are observed to increase with temperature. At lower temperatures, a size dependent growth rate is observed suggesting that condensed-phase chemistry may be important for particle growth. Using the change in aerosol chemical composition during growth events, we infer that growth driven by a combination of organic and inorganic compounds is typically faster than growth by either inorganic or organic compounds only. Back trajectory analysis provides insight into potential sources of the gas-phase precursors. We use these results to investigate how particle growth influences the concentration of cloud condensation nuclei at the site.