Citation:

Xu, L., H. Pye, J. He, Y. Chen, B. Murphy, AND N. Ng. Experimental and model estimates of the contributions from biogenic monoterpenes and sesquiterpenes to secondary organic aerosol in the southeastern United States. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 18(17):12613-12637, (2018). https://doi.org/10.5194/acp-18-12613-2018

Impact/Purpose:

Experiments observing the formation of secondary organic aerosol were conducted on the roof facility at Georgia Tech campus. These experiments found substantial production of SOA from the oxidation of monoterpenes. The CMAQ model was improved to describe this formation pathway with data from North Carolina State University that was consistent with the observations from the experiments. With this approach in place, the model reproduced the observations in the ambient environment extremely well and was able to predict the majority of biogenic SOA mass, a goal that had not yet been accomplished with a chemical transport model.

Description:

Atmospheric organic aerosol (OA) has important impacts on climate and human health but its sources remain poorly understood. Biogenic monoterpenes and sesquiterpenes are important precursors of secondary organic aerosol (SOA), but the amounts and pathways of SOA generation from these precursors are not well constrained by observations. We propose that the less-oxidized oxygenated organic aerosol (LO-OOA) factor resolved from positive matrix factorization (PMF) analysis on aerosol mass spectrometry (AMS) data can be used as a surrogate for fresh SOA from monoterpenes and sesquiterpenes in the southeastern US. This hypothesis is supported by multiple lines of evidence, including lab-in-the-field perturbation experiments, extensive ambient ground-level measurements, and state-of-the-art modeling. We performed lab-in-the-field experiments in which the ambient air is perturbed by the injection of selected monoterpenes and sesquiterpenes, and the subsequent SOA formation is investigated. PMF analysis on the perturbation experiments provides an objective link between LO-OOA and fresh SOA from monoterpenes and sesquiterpenes as well as insights into the sources of other OA factors. Further, we use an upgraded atmospheric model and show that modeled SOA concentrations from monoterpenes and sesquiterpenes could reproduce both the magnitude and diurnal variation of LO-OOA at multiple sites in the southeastern US, building confidence in our hypothesis. We estimate the annual average concentration of SOA from monoterpenes and sesquiterpenes in the southeastern US to be roughly 2µgm−3.

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