Johan P. Beukes

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.

Submicrometer aerosols and excess CO as tracers for biomass burning air mass transport over southern Africa

This paper links surface measurements of biomass burning aerosols and trace gases with trajectory analysis to determine transport pathways for air masses with high and low concentrations. We interpret the long-term atmospheric monitoring record from a remote monitoring station in central southern Africa (North West Province, South Africa). Trace gas analyzers and a Differential Mobility Particle Sizer were used to measure ground level trace gas and submicron aerosol concentrations. Fire signatures were identified based on excess CO above average tropospheric levels, and episodes of enhanced particulate matter concentrations in the 10 to 840 nm size range. Thirty-six biomass burning plumes were reported; 7 had strong signals of excess CO, with ratios between 0.41 and 0.64, while 29 had weak signals ranging between 0.07 and 0.32. Pathways identified for the long-range transport of biomass burning aerosols were as follows: easterly (39% frequency), southwesterly (31%), recirculation (22%), and northerly (8%) flow patterns. CO and Aitken-mode aerosol number strengths were larger for fire emissions arriving in the easterly and southwesterly air masses than for recirculation and northerly air masses. Easterly and southwesterly flows were dominated by Aitken-mode aerosol, whereas accumulation-mode particles dominated in the recirculation and northerly flows. Findings identify biomass burning as a major source of Aitken-mode aerosols. Enhanced CO concentrations, combined with Aitken- and accumulation-mode particle number size distributions, are shown to provide a useful signature of plumes originating over regional biomass combustion events.

Comparison of physical properties of oxidative sintered pellets produced with UG2 or metallurgical-grade South African chromite: A case study

Synopsis The physical properties of oxidative sintered pellets produced from typical South African UG2 ore are compared with the physical properties of pellets produced with conventional South African metallurgical-grade chromite ore (from the Lower Group 6 or the Middle Group 1 and 2 seams). A statistical evaluation of the cured (sintered) compressive strengths proved that pellets prepared from UG2 ore are likely to have the same, or better, compressive strength than pellets prepared from metallurgical-grade chromite ore. The cured abrasion strength of the UG2 pellets was also superior to that of the metallurgical-grade pellets. Scanning electron microscopy (SEM) backscatter, secondary electron, and elemental X-ray mapping were used to determine the reasons for the general superior strength of the UG2 pellets. The case study UG2 ore also required 13 kWh/t less energy for milling to attain the required particle size distribution prior to pelletization, which can lead to substantial cost savings. Results presented in this paper can be utilized by ferrochromium (FeCr) producers to better quantify the advantages and disadvantages associated with the use of UG2 ore for FeCr production.

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...

Major secondary aerosol formation in southern African open biomass burning plumes

Open biomass burning contributes significantly to air quality degradation and associated human health impacts over large areas. It is one of the largest sources of reactive trace gases and fine particles to Earth’s atmosphere and consequently a major source of cloud condensation nuclei on a global scale. However, there is a large uncertainty in the climate effect of open biomass burning aerosols due to the complexity of their constituents. Here, we present an exceptionally large dataset on southern African savannah and grassland fire plumes and their atmospheric evolution, based on 5.5 years of continuous measurements from 2010 to 2015. We find that the mass of submicrometre aerosols more than doubles on average, in only three hours of daytime ageing. We also evaluate biomass burning aerosol particle size distributions and find a large discrepancy between the observations and current model parameterizations, especially in the 30–100 nm range. We conclude that accounting for near-source secondary organic aerosol formation and using measurement-based size distribution parameterizations in smoke plumes is essential to better constrain the climate and air quality effects of savannah and grassland fires.A substantial amount of secondary aerosols form within hours of biomass burning in southern African savannah and grassland fires, according to analyses of 5.5 years of continuous field measurements.

The use of satellite observations of fire radiative power to estimate the availabilities (activity patterns) of pyrometallurgical smelters

emission inventories (how much of what pollutant species are emitted, where and when) are poorly developed in many countries. South Africa, which is the largest industrialized economy in southern Africa, can be considered as an example. At present South African environmental legislation requires significant atmospheric emitters to supply emission data to the government, but this information is protected by some legal safeguards and this has thus far prevented a comprehensive peer-reviewed emission inventory from becoming available in the public domain. Applications can be made to the Air Pollution Control Officer to access some information on the atmospheric emission licences of the aforementioned emitters, but this process is lengthy and does not yield all the required information. Therefore, atmospheric modelling studies undertaken for this region have to a large extent depended on global emission inventory databases (e.g. Kuik et al., 2015; Lourens et al., 2016) that might not contain sufficient detail. Also, it is almost impossible for atmospheric scientists to account for fluctuations in the temporal activity patterns (if a source emits or not) of large point sources so as to provide temporally resolved emission inventories. In this paper we demonstrate how satellitederived fire data can be used to locate and reflect the activity patterns of large point sources. Open biomass burning, both natural (e.g. lighting-induced fires) and anthropogenic (e.g. intentional or accidental grassland, savannah, or forest fires), has long been recognized as one of the most significant sources of atmospheric pollutant species such as carbon dioxide (CO2), carbon monoxide (CO), particulate matter (PM), black carbon (BC), and precursors for secondary pollutants (e.g. Vakkari et al., 2014; Chiloane et al., 2017). This has led to a multitude of studies using satellite-derived fire and/or burned area detection data to improve fire emission estimates and explain pollutant observations (e.g. Mafusire et al., 2016). However, comparatively little attention has been given to alternative uses of these satellite-derived fire data-sets.

The sensitivity of Afromontane tarns in the Maloti-Drakensberg region of South Africa and Lesotho to acidic deposition

Despite their remoteness from sources of atmospheric pollutant emissions, the Afromontane tarns in the Maloti-Drakensberg region are perfect candidates to study the negative effects of acidifying atmospheric pollution, because mountain lakes are widely recognised as sentinel ecosystems, unimpacted by direct human disturbance within their catchments. Thirty-four tarns were sampled in the Maloti-Drakensberg region and most were found to be extremely sensitive to acidic deposition, as indicated by their low acid neutralising capacity. There are very few studies of freshwater critical loads for any region within South Africa. The steady-state water chemistry model (SSWC) was adapted and used to determine critical loads, whereas exceedance was estimated relative to modelled regional deposition data, in order to understand the risk of harmful effects to aquatic ecosystems. Seventy-six percent of sampled sites across the Maloti-Drakensberg would exceed critical loads even at the lowest modelled deposition levels, but there are no current measured deposition data for the region. The sensitivity of the Maloti-Drakensberg tarns needs to be considered in future policy formulation regarding acceptable levels of acidifying atmospheric pollution from South Africa’s energy sector and indicates the need for assessing aquatic ecosystem impacts in other regions of South Africa.