Vertical Gradients in New Particle Formation and Growth: Influence of Agricultural Emissions
Bri Dobson, Daniel Katz, Mitchell Alton, Harald Stark, Tamanna Subba, Douglas Worsnop, Chongai Kuang, Manjula Canagaratna, ELEANOR BROWNE, University of Colorado Boulder & CIRES
Abstract Number: 539
Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene
Abstract
Agricultural activities ranging from changing land and water use to the application of fertilizer have been a defining characteristic of the Anthropocene. Increased demands for food and biofuel as well as changes in environmental factors will alter agricultural emissions in the coming decades. How aerosol processes respond to such changes remains an open question with implications for future agricultural productivity and ecosystem and human health. To address these knowledge limitations, we have been investigating new particle formation and growth across multiple seasons at the United States Department of Energy Southern Great Plains research facility in Lamont, Oklahoma, an agriculturally intensive region. We use measurements of particle formation precursors (e.g., NH3, amines, H2SO4, oxygenated organic molecules (OOMs)) at the surface, vertically resolved measurements of 1-3 nm aerosol-cluster concentration from the tethered ballon system, and WRF-Chem modeling. We have found that agricultural emissions of reactive nitrogen compounds, namely NH3, amines, and nitrogen oxides play a central role in nucleation and growth processes. Due to the relatively high surface temperatures and low sulfuric acid concentrations, new particle formation is generally favored aloft. A notable exception occurs when amines are present, and cluster growth is observed at the surface. WRF-Chem results suggest that vertical mixing of NH3 may play a defining role in determining the variability in boundary layer profiles of nucleation. High NO mixing ratios affect the formation of OOMs, specifically by depressing the formation of “dimer” molecules formed from peroxy radical cross reactions. As a result, sesquiterpene oxidation products rather than monoterpene oxidation products dominate the extremely low volatility compounds that contribute to growth, a finding consistent with emission factors from crops in the area. Overall, these findings highlight that future prediction of aerosol processes in agricultural regions requires improved understanding of agricultural emissions.