Kerneels Jaars

Rapid changes in biomass burning aerosols by atmospheric oxidation

Partially funded by the Academy of Finland (132640, Finnish Centre of Excellence 141135), the Saastamoinen Foundation, and the North-West University (South Africa)

Reevaluating the contribution of sulfuric acid and the origin of organic compounds in atmospheric nanoparticle growth

Aerosol particles formed in the atmosphere are important to the Earths climate system due to their ability to affect cloud properties. At present, little is known about the atmospheric chemistry responsible for the growth of newly formed aerosol particles to climate-relevant sizes. Here combining detailed aerosol measurements with a theoretical framework we found that depending on the gaseous precursors and size of the newly formed particles, the growth was dominated by either sulfuric acid accompanied by ammonium or organic compounds originating in either biogenic emissions or savannah fires. The contribution of sulfuric acid was larger during the early phases of the growth, but in clean conditions organic compounds dominated the growth from 1.5 nm up to climatically relevant sizes. Furthermore, our analysis indicates that in polluted environments the contribution of sulfuric acid to the growth may have been underestimated by up to a factor of 10.

Chapter 20 - Ozone Concentrations and Their Potential Impacts on Vegetation in Southern Africa

Abstract The tropospheric ozone concentrations over southern Africa are relatively high due to large precursor emissions from biomass burning, vegetation and anthropogenic sources and the intensity of solar radiation. In this study, we summarize ozone concentration data from both literature and new measurements. Further, we present data on the accumulated vegetation exposure to ozone in terms of the AOT40 index, which is calculated for the sites with hourly ozone and radiation data, with an aim to assess the potential for adverse effects on vegetation. As the seasonal variation of ozone concentrations is large, we discuss the effect of growing season onset on the stomatal gas exchange and the related potential for vegetation impacts. Finally, future research needs are discussed.

Estimating the concentration of nucleation mode aerosol particles over South Africa using satellite remote sensing measurements

In this work satellite based observations were used to estimate the concentration of nucleation mode aerosols over South Africa. The nucleation mode aerosols can not be detected directly with satellite instruments since they are much smaller than the optically active aerosols, hence the concentrations were estimated using proxies introduced by Kulmala et al. (2011). Results showed enhanced values of both primary and regional scale nucleation proxies over the Mpumalanga Highveld industrial area, whereas over the Johannesburg-Pretoria megacity only the primary nucleation proxy showed elevated values. To estimate how well satellite based proxies work, the relation between satellite and in situ based quantities was studied in more detail. The correlation between aerosol optical depth (AOD) and condensation sink (CS) was 0.2-0.3 depending on the location. Boundary layer height affected the correlation somewhat, but there are other factors, such as the effect of dust on AOD, that are more likely to have a stron...