Understanding particle growth events response to changes in hydrocarbons and sulfur dioxide for a rural/urban site in Beltsville, Maryland

Abstract:

Aerosol formation events have been studied in depth over the past few decades, yet large uncertainties remain on the mechanisms responsible for the generation of new particles. At a rural/urban research facility in Beltsville, MD ultrafine and fine mode aerosol number and size distributions were collected during July 2011 along with volatile organic compounds canister samples. Multiple particle growth events (PGEs) were detected during the summer and occurred on days following strong synoptic cold frontal passages. Though these events occurred in clean air masses, moderate sulfur dioxide (SO₂) mixing ratios were observed during the PGEs. A chemical-box with the Regional Atmospheric Chemistry Mechanism, version 2 (RACM2) was used to simulate the gas-phased chemical species concentrations during the PGEs. Simulated chemical mixing ratios from the RACM2 box model were used as input to an equilibrium aerosol model, the Simulating Composition of Atmospheric Particle at Equilibrium, version 2 (SCAPE2) that was used to estimate the state and composition of the aerosols. The goal of this research was to determine whether SO₂ was contributing to the growth of the PGEs and to have a better understanding of the mechanism responsible for the formation of the PGEs. This research is significant because some of the largest uncertainties in observations and model results are determining the mechanisms that create and grow new particles throughout the lower atmosphere and their role on air quality, cloud formation, and climate.