PNNL

Abstract

The GoAmazon 2014/5 field campaign took place in Manaus (Brazil) and allowed to investigate the interaction between background level biogenic air masses and anthropogenic plumes. We present in this work a box model built to simulate the impact of the urban chemistry on the biogenic Secondary Organic Aerosol (SOA) formation and composition. An organic chemistry mechanism is generated with the Generator for Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to simulate the explicit oxidation of biogenic and anthropogenic compounds. A parameterization is also included to account for the reactive uptake of isoprene oxidation products on aqueous particles. After adjusting biogenic emissions because the existing emission inventory overestimates them, the model is able to reproduce measured primary compounds, ozone and NOx for clean or polluted situations. The explicit model is able reproduce background case SOA mass concentrations but is underestimating the enhancement observed in the urban plume. Oxidation of biogenic compounds is the major contributor to SOA mass. A Volatility Basis Set parameterization (VBS) applied to the same cases obtains better results for predicting SOA mass in the box model. The explicit mechanism may be missing SOA formation processes related to the oxidation of monoterpenes that could be implicitly accounted for in the VBS parameterization.