AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Observations of Strong Secondary Aerosol and Ozone Formation in Biomass Burning Plumes in Southern Africa
VILLE VAKKARI, Johan Paul Beukes, Miroslav Josipovic, Pieter G. van Zyl, Finnish Meteorological Institute, Helsinki, Finland
Abstract Number: 449 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Biomass burning (BB) is a major source of aerosol particles and trace gases globally with significant implications for air quality and climate. Particulate matter (PM) emissions and ozone (O3) formation during plume transport can degrade air quality hundreds of kilometers away from the fire. Simultaneously, the large variability in BB emissions exerts significant uncertainty in climate predictions. Globally, one of the largest sources of BB aerosols is southern Africa, where savanna and grassland fires are frequent during the dry season from June to October. Here, we utilize continuous measurements of submicron aerosol size distribution, black carbon (BC) and trace gases at Welgegund, South Africa (26.57S, 26.94E) from May 2010 to January 2016. During this period we identified 130 smoke episodes totalling >400h of in-plume measurements. We observed strong secondary aerosol formation in smoldering daytime plumes with >3x PM enhancement in less than 4h of ageing. Also O3 formation was substantial during daytime ageing, with excess O3 to excess CO ratio reaching 0.25 for >3h old smoldering plumes. In flaming cases no net PM increase occurred, resulting in an average increase in PM by a factor of 2. This suggests that a major fraction of the discrepancy between top-down and bottom-up BB emission estimates may be due to missing near-fire secondary aerosol formation. Furthermore, secondary aerosol formation during ageing affects strongly the submicron size distribution: during the first 3h we observed modal mean diameter grow from 70nm to 120nm.