AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Fast Secondary Aerosol Formation in Biomass Burning Plumes in Southern Africa
VILLE VAKKARI, Johan Paul Beukes, Kerneels Jaars, Miroslav Josipovic, Andrew D. Venter, Pieter G. van Zyl, Finnish Meteorological Institute, Helsinki, Finland
Abstract Number: 279 Working Group: Combustion
Abstract Biomass burning (BB) is one of the largest sources of reactive trace gases and fine particles in the Earth’s atmosphere. However, there is large uncertainty in the climate effect of the BB emissions, mostly because of the reactive species co-emitted with black carbon (BC) particles. We investigated the temporal evolution of BB smoke in southern Africa utilizing continuous in-situ aerosol measurements at Welgegund, South Africa (26.57S, 26.94E, 1480 m above sea level) from 20 May 2010 to 31 December 2014. Of the measurements performed at Welgegund (welgegund.org), we used aerosol particle number size distribution, carbon monoxide (CO), BC with a MAAP, local wind and solar radiation. Submicron particulate mass (PM1) was estimated from the number size distribution; the ratio of excess BC to excess CO was used to characterize the flaming to smoldering ratio of the fire.
During the nearly five year period we were able to identify 118 BB plumes. For 83 plumes the location of the fire could be identified from MODIS burnt area and/or SEVIRI fire radiative power observations. For these episodes – a total of 250 hours of in-plume sampling – we could estimate the plume age. We observed fast secondary aerosol formation in nearly all plumes transported under daylight conditions: in smoldering cases up to a factor of 4 increase in excess PM1 to excess CO ratio occurred in less than 5 hours. Only the flaming-dominated BB plumes did not exhibit significant secondary aerosol formation during daytime. In night-time plumes the secondary aerosol formation was much slower and during very calm nights a decrease in the excess PM1 to excess CO ratio was frequently observed. In conclusion, our observations indicate that secondary aerosol formation in BB plumes depends strongly on both the emission (flaming vs. smoldering fire) and the oxidizing capacity of the atmosphere during plume transport.