Stuart Piketh - Academia.edu (original) (raw)

Papers by Stuart Piketh

Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numeri... more Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numerical weather prediction models, allowing for regional and case-specific parameterisation of cloud condensation nuclei (CCN) and cloud droplet interactions. In this paper, the Thompson aerosol-aware microphysics scheme, within the Weather Research and Forecasting (WRF) model, is used for two fog cases during September 2017 over Namibia. Measurements of CCN and fog microphysics were undertaken during the AErosols, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) field campaign at Henties Bay on the coast of Namibia during September 2017. A key concept of the microphysics scheme is the conversion of water-friendly aerosols to cloud droplets (hereafter referred to as CCN activation), which could be estimated from the observations. A fog monitor 100 (FM-100) provided cloud droplet size distribution, number concentration (N t), liquid water content (LWC), and mean volumetric diameter (MVD). These measurements are used to evaluate and parameterise WRF model simulations of N t , LWC, and MVD. A sensitivity analysis was conducted through variations to the initial CCN concentration, CCN radius, and the minimum updraft speed, which are important factors that influence droplet activation in the microphysics scheme of the model. The first model scenario made use of the default settings with a constant initial CCN number concentration of 300 cm −3 and underestimated the cloud droplet number concentration, while the LWC was in good agreement with the observations. This resulted in droplet size being larger than the observations. Another scenario used modelled data as CCN initial conditions, which were an order of magnitude higher than other scenarios. However, these provided the most realistic values of N t , LWC, MVD, and droplet size distribution. From this, it was concluded that CCN activation of around 10 % in the simulations is too low, while the observed appears to be higher reaching between 20 % and 80 %, with a mean (median) of 0.55 (0.56) during fog events. To achieve this level of activation in the model, the minimum updraft speed for CCN activation was increased from 0.01 to 0.1 m s −1. This scenario provided N t , LWC, MVD, and droplet size distribution in the range of the observations, with the added benefit of a realistic initial CCN concentration. These results demonstrate the benefits of a dynamic aerosol-aware scheme when parameterised with observations.

The formation of a river of smoke crossing southern Africa was investigated during the Aerosols, ... more The formation of a river of smoke crossing southern Africa was investigated during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) campaign in September 2017. A complementary set of global and mesoscale numerical simulations as well as ground-based, airborne and space-borne observations of the dynamics, thermodynamics and composition of the atmosphere are used to characterize the river of smoke in terms of timing and vertical extent of the biomass burning aerosol (BBA) layer. The study area was under the synoptic influence of a coastal low rooted in a tropical easterly wave and a high-pressure system over the continent and westerly waves at mid latitudes, one of which had an embedded cutoff low (CoL). The coastal low interacted with the second of two approaching westerly waves and ultimately formed a mid-level tropical temperate trough (TTT). The TTT created the fast-moving air mass transported to the southwestern Indian Ocean as a river of smoke. The CoL, which developed and intensified in the upper levels associated with the first (easternmost) westerly wave, remained stationary above northern Namibia prior to the formation of the TTT and was responsible for the thickening of the BBA layer. This shows that the evolution of the river of smoke is very much tied to the evolution of the TTT, while its vertical extent is related to the presence of the CoL. The mechanisms by which the CoL, observed over Namibia in the entrance region of the river of smoke, influences the vertical structure of the BBA layer is mainly associated with the ascending motion above the BBA layer. In the presence of the CoL, the top of the BBA layer over northern Namibia reaches altitudes above 8 km. This is much higher than the average height of the top of the BBA layer over the regions where the smoke comes from (Angola, Zambia, Zimbabwe, Mozambique), which is 5 to 6 km. The results suggest that the interaction between the TTTs and the CoLs which form during the winter may have a role in promoting the transport of BBA from fire-prone regions in the tropical band to the temperate mid latitudes and the southwestern Indian Ocean.

Toxics, 2022

Emissions from residential solid fuels reduce ambient air quality and cause indoor air pollution ... more Emissions from residential solid fuels reduce ambient air quality and cause indoor air pollution resulting in adverse human health. The traditional solid fuels used for cooking include coal, straws, dung, and wood, with the latter identified as the prevalent energy source in developing countries. Emissions from such fuel sources appear to be significant hazards and risk factors for asthma and other respiratory diseases. This study aimed at reporting factors influencing the choice of dominant solid fuel for cooking and determine the emission risk from such solid fuel in three villages of Phalaborwa, Limpopo province, South Africa. The study used descriptive analysis to show the relationship between the socio-economic variables and the choice of cooking fuel at the household level. Multiple correspondence analysis (MCA) was used further to detect and represent underlying structures in the choice of dominant fuels. MCA shows the diversity and existing relationship of how variables are ...

Clean Air Journal, 2017

Satellite retrievals have highlighted the South African Highveld as a region with one of the high... more Satellite retrievals have highlighted the South African Highveld as a region with one of the highest nitrogen oxide (NOx) emission densities in the world. There are numerous sources of NOx on the Highveld, including coal-fired power stations, petrochemical and other industries, motor vehicles and lightning, but surface measurements of NOx have not indicated that there is any cause for concern. A number of research initiatives are being undertaken in an attempt to resolve the discrepancy between surface measurements and satellite retrievals of NOx. An assessment of ground-level concentrations in various environments, including industrial and urban regions, has shown that NOx levels recorded in the low-income urban area are significantly higher than those recorded downwind of industries or power stations. NO2 column densities have been remotely sensed over the Highveld using an airborne imaging Differential Optical Absorption Spectrometer (iDOAS), in order to validate the satellite re...

Atmosphere, 2021

Emissions from residential solid fuel burning in densely populated low-income settlements is a si... more Emissions from residential solid fuel burning in densely populated low-income settlements is a significant source of air pollution over the South African Highveld. The area is densely populated and highly industrialized, resulting in high concentrations of pollutants over the area. Although emissions from industrial sources are much larger, exposure to household emissions poses the most significant risk to human health. Interventions aimed at reducing solid fuel burning in low-income settlements on the Highveld have the potential to reduce exposure, but quantifying their true impact remains a challenge. We aimed to estimate the health and associated economic benefits of the regional implementation of thermal insulation as intervention measure in low-income settlements to predict the potential impact on the regional scale. We used a land use type regression model to estimate pre-intervention PM2.5 concentrations over the Highveld and then used sampled post-intervention air quality da...

Clean Air Journal, 2021

Understanding how exposure to particulate matter impacts human health is complex. Personal exposu... more Understanding how exposure to particulate matter impacts human health is complex. Personal exposure is a function of the pollution concentrations measured at any given place and time. The health impacts of this exposure are, amongst other factors, determined by how high pollutant concentrations are and what enters the body. This study considered data gathered in the winter of 2013 in a low-income community on the Mpumalanga Highveld, South Africa, which is a geographical area known for its high air pollution levels. Time-activity data collected by GPS monitors worn by individuals in the community were used to understand in which microenvironments people spend most of their time. Eight days’ worth of ambient, indoor and personal particulate matter measurements were paired with individual GPS positioning data for one study participant. We identified pollutant concentrations where the person spent time and how much particulate matter was potentially inhaled in specific micro-environmen...

We currently have a limited understanding of the spatial and temporal variability in vertically s... more We currently have a limited understanding of the spatial and temporal variability in vertically stratified atmospheric layers over Namibia and the southeast Atlantic (SEA) Ocean. Stratified layers are relevant to the transport and dilution of local and long-range transported atmospheric constituents. This study used eleven years of global positioning system radio occultation (GPS-RO) signal refractivity data (2007-2017) over Namibia and the adjacent ocean surfaces, and three years of radiosonde data from Walvis Bay, Namibia, to study the character and variability in stratified layers. From the GPS-RO data and up to a height of 10 km, we studied the spatial and temporal variability in the point of minimum gradient in refractivity, and the temperature inversion height, depth and strength. We also present the temporal variability of temperature inversions and the boundary layer height (BLH) from radiosondes. The BLH was estimated by the parcel method, the top of a surface-based inversion, the top of a stable layer identified by the bulk Richardson number (RN), and the point of minimum gradient in the refractivity (for comparison with GPS-RO data). A comparison between co-located GPS-RO to radiosonde temperature profiles found good agreement between the two, and an average underestimation of GPS-RO to radiosonde temperatures of-0.45 ± 1.25°C, with smaller differences further from the surface and with decreasing atmospheric moisture content. The minimum gradient (MG) of refractivity, calculated from these two datasets were generally in good agreement (230 ± 180 m), with an exeption of a few cases when differences exceeded 1000 m. The surface of MG across the region of interest was largely affected by macroscale circulation and changes in atmospheric moisture and cloud, and was not consistent with BLH(RN). We found correlations in the character of low-level inversions with macroscale circulation, radiation interactions with the surface, cloud cover over the ocean and the seasonal maximum in biomass burning over southern Africa. Radiative cooling on diurnal scales also affected elevated inversions between 2.5 and 10km, with more co-occurring inversions observed at night and in the morning. Elevated inversions formed most frequently over the subcontinent and under subsidence by highpressure systems in the colder months. Despite this macroscale influence peaking in the winter, the springtime inversions, like those at low levels, were strongest.

Clean Air Journal, 2014

Domestic burning activities, specifically in informal settlements, contribute greatly to the air ... more Domestic burning activities, specifically in informal settlements, contribute greatly to the air quality problems experienced by most developing urban centres. Low-income households that exist within townships in South Africa house a large portion of the South African population. These households burn vast quantities of coal, wood and other substances to provide for their energy needs. Pollutants emitted as a result of domestic burning are estimated to be one of the leading causes of respiratory illnesses in inhabitants of townships. To better understand the relationship that exists between domestic burning and the resultant pollutants, a method of quantifying these pollutants has been developed for a completely un-electrified settlement, near Johannesburg, using the quantities and type of fuel consumed. Seasonality, availability, price and cultural aspects all have a bearing on the fuel source choice and the quantity consumed. The most significant temporal observations identified f...

Clean Air Journal, 2020

The quality of air breathed in South Africa is of great concern, especially in industrialised reg... more The quality of air breathed in South Africa is of great concern, especially in industrialised regions where PM2.5 concentrations are high. Long term exposure to PM2.5 is associated with serious adverse health impacts. Traditionally, PM2.5 is monitored by a network of ground-based instruments. However, the coverage of monitoring networks in South Africa is not dense enough to fully capture the spatial variability of PM2.5 concentrations. This study explored whether satellite remote sensing could offer a viable alternative to ground-based monitoring. Using an eight-year record (2009 to 2016) of satellite retrievals (MODIS, MISR and SeaWIFS) for PM2.5 concentrations, spatial variations and temporal trends for PM2.5 are evaluated for the Vaal Triangle Airshed Priority Area (VTAPA). Results are compared to corresponding measurements from the VTAPA surface monitoring stations. High PM2.5 concentrations were clustered around the centre and towards the south-west of the VTAPA over the highl...

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, ye... more Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a 5-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three intensive observation periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June-October), aerosol particles reaching 3-5 km in altitude are transported westward over the southeast Atlantic, where they interact with one of the largest subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, as well as due to the parameterized treatment of physical processes.

South African Journal of Science, 2020

Biomass burning in Africa provides a prolific source of aerosols that are transported from the so... more Biomass burning in Africa provides a prolific source of aerosols that are transported from the source region to distant areas, as far away as South America and Australia. Models have long predicted the primary outflow and transport routes. Over time, field studies have validated the basic production and dynamics that underlie these transport patterns. In more recent years, the advancement of spaceborne active remote-sensing techniques has allowed for more detailed verification of the models and, importantly, verification of the vertical distribution of the aerosols in the transport regions, particularly with respect to westerly transport over the Atlantic Ocean. The Cloud-Aerosol Transport System (CATS) lidar on the International Space Station has detection sensitivity that provides observations that support long-held theories of aerosol transport from the African subcontinent over the remote Indian Ocean and as far downstream as Australia. Significance: Biomass burning in Africa ca...

Atmosphere, 2018

There is still a pressing concern regarding the causes of poor indoor air quality and the consequ... more There is still a pressing concern regarding the causes of poor indoor air quality and the consequent effects on health, because people spend a considerable amount of time indoors. Information about seasonal variation and the determinants of particulate matter (PM) concentrations could guide the design and implementation of intervention strategies. This study was conducted in Giyani, Limpopo province, South Africa. The main aim was to assess indoor air quality. Indoor PM and temperature were monitored to describe seasonal and diurnal patterns of indoor PM 4 concentration and to estimate the association between PM concentrations and indoor as well as ambient conditions. Indoor PM 4 was monitored hourly in kitchens for the duration of spring (September), summer (February) and winter (July). Indoor temperatures were monitored hourly in kitchens, living rooms and bedrooms. Outdoor temperature and outdoor relative humidity were also monitored for the same period. Indoor temperatures showed a large range in the three sampled seasons, with the maximum values raising the largest cause for concern. Maximum indoor temperatures in summer exceeded the threshold of 35 • C, which has been shown to have adverse health effects. Occupants of the sampled households were exposed to indoor PM 4 concentrations that exceeded national and international guidelines. Hourly indoor temperature was statistically significantly correlated to PM 4 concentrations in the summer and spring (r = 0.22 and 0.24 respectively, p < 0.001 for both) and negatively correlated to outdoor relative humidity (r = −0.27, p < 0.001). Diurnal PM 4 variations showed pronounced patterns with morning and evening peaks. PM 4 was consistently higher throughout the day in summer compared to spring and winter. Community-based intervention strategies should consider these seasonal differences in PM 4 exposure and tailor awareness messages for exposure prevention accordingly.

Clean Air Journal, 2018

Residential burning of solid fuels is a major source of fine particulate matter (PM2.5), which de... more Residential burning of solid fuels is a major source of fine particulate matter (PM2.5), which degrades indoor and ambient air quality in low-income settlements. The adverse impact of fine particulate emissions on the environment and human health is well-documented in other countries such as China and India; however, there is need for local studies to report on emission factors from residential burning of solid fuels. An emission factor quantifies the total mass of a pollutant emitted per amount of fuel burned. Emission factor is an input parameter in air quality modelling to forecast a pollutant concentrations over time and when calculating total emissions from a specific source. Local emission factors are central to managing air quality for they give results that are representative of the source compared with international emission factors. Quantifying emissions, understanding household fuel use patterns and interaction with the stove (stove operation behaviour) during a burning e...

Clean Air Journal, 2019

Coal-fired power plants are considered a major source of criteria air pollutants. The existence o... more Coal-fired power plants are considered a major source of criteria air pollutants. The existence of such activities close to densely populated areas has an impact on human health and more generally on the environment. The impact of a pollutant typically depends on its residence time and the existence of background concentration levels. This study evaluates the dispersion of PM2.5, SO2 and NOX emissions from Eskom power plants (Arnot, Hendrina, and Komati) located close to KwaZamokuhle Township. AERMOD was used to assess the contribution of each plant to the air quality of the township. This steady-state dispersion model was used to simulate surface concentrations (1-hour, 24-hour and annual average concentrations) on a 50km domain for 2015-2017. The modelled results together with data obtained from Eskom’s KwaZamokuhle monitoring site were used to estimate the extent to which these power plants contribute to the ambient air quality of KwaZamokuhle Township. The results confirm that t...

Clean Air Journal, 2019

The South African Highveld is a portion on the inland plateau characterized by low winter ambient... more The South African Highveld is a portion on the inland plateau characterized by low winter ambient temperatures. Studies done in several climatic regions around the world have found a positive relationship between inadequate housing and low indoor temperatures during the winter season. Prolonged exposure to low indoor temperature is a threat to human physical health. This study characterizes indoor human thermal comfort conditions in typical low-income residential dwellings during the winter season. Mapping indoor human thermal comfort can assist in exploring the potential for domestic thermal insulation retrofits interventions. In-situ temperature measurements were done in 2014, 2016 and 2017 across three Highveld settlements of kwaZamokuhle, kwaDela, and Jouberton. The sample included a mixture of old (pre-1994), post 1994 Reconstruction and Development Programme (RDP) as well as non-RDP structures. Findings were that 88% of sampled dwellings in Jouberton 2016, 86% in Jouberton 201...

Journal of Geophysical Research: Atmospheres, 2014

Surface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NO x = ... more Surface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NO x = NO + NO 2) and volatile organic compounds in the presence of sunlight. In this work we examine effects of the climate pattern known as the El Niño-Southern Oscillation (ENSO) and NO x variability on surface ozone from 1990 to 2007 over the South African Highveld, a heavily populated region in South Africa with numerous industrial facilities. Over summer and autumn (December-May) on the Highveld, El Niño, as signified by positive sea surface temperature (SST) anomalies over the central Pacific Ocean, is typically associated with drier and warmer than normal conditions favoring ozone formation. Conversely, La Niña, or negative SST anomalies over the central Pacific Ocean, is typically associated with cloudier and above normal rainfall conditions, hindering ozone production. We use a generalized regression model to identify any linear dependence that the Highveld ozone, measured at five air quality monitoring stations, may have on ENSO and NO x. Our results indicate that four out of the five stations exhibit a statistically significant sensitivity to ENSO at some point over the December-May period where El Niño amplifies ozone formation and La Niña reduces ozone formation. Three out of the five stations reveal statistically significant sensitivity to NO x variability, primarily in winter and spring. Accounting for ENSO and NO x effects throughout the study period of 18 years, two stations exhibit statistically significant negative ozone trends in spring, one station displays a statistically significant positive trend in August, and two stations show no statistically significant change in surface ozone. BALASHOV ET AL.

South African Journal of Science, 2011

We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South... more We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South African central industrial area, poses an environmental threat across a larger region within the dispersal footprint. A network of 37 passive monitoring sites to measure SO 2 and NO 2 was operated from August 2005 to September 2007. The area extended over the entire northern and eastern interior of South Africa. Monitoring locations were chosen to avoid direct impacts from local sources such as towns, mines and highways. Dry deposition rates of SO 2 and NO 2 were calculated from the measured concentrations. Concentrations of sulphur and nitrogen species in wet deposition from a previous study were used in conjunction with measured rainfall for the years 2006 and 2007 to estimate the wet deposition over the region. The calculated total (non-organic) acidic deposition formed the basis for an assessment of exceedance of critical loads based on sensitivity of the regional soils. Regional soil sensitivity was determined by combining two major soil attributes available in the World Inventory of Soil Emission Potentials (International Soil Reference and Information Centre). Results indicate that certain parts of the central pollution source area on the South African Highveld have the potential for critical load exceedance, while limited areas downwind show lower levels of exceedance. Areas upwind and remote areas up and downwind, including forested areas of the Drakensberg escarpment, do not show any exceedance of the critical loads.

South African Journal of Science, 2010

Atmospheric reactive nitrogen concentrations on the South African Highveld have become a growing ... more Atmospheric reactive nitrogen concentrations on the South African Highveld have become a growing concern, with satellite images indicating very high nitrogen dioxide (NO 2) concentrations in the region. This study investigated the nitrogen budget on the Highveld through the analysis of the concentration of the atmospheric nitrogen species on a temporal scale as well as the atmospheric conversion, transport and removal of these species. Data were collected at Eskom's Elandsfontein ambient air quality monitoring site, which is centrally located on the industrialised Highveld. A year's dataset from 2005 and 2006 was analysed and it was found that nitrogen oxide (NO x) concentrations were higher in winter as a result of stable atmospheric conditions, as well as prevalent westerly and north-westerly airflow, which transported emissions directly from the nearby power station sources to the monitoring site. Nitrate (NO 3) concentrations also peaked during winter, with a distinct biomass burning peak during August 2005. Diurnally, NO x concentrations indicated a tall-stack industrial source, where concentrations peaked at midday. The NO 3 concentrations were higher at night than during the day; during the day the NO 3 radical is rapidly photolysed and nitrates cannot be produced. Case studies indicated that the conversion rate of nitric oxide (NO) to NO 2 was highly variable as a result of varying atmospheric factors, which include time of day, dispersion, stability and regional atmospheric chemistry. These rates ranged from 11% to 59% per hour. Rates of dry deposition of NO, NO 2 and NO 3 were generally higher during winter as a result of higher atmospheric concentrations and increased atmospheric stability. Nitrogen was predominantly deposited as NO 2 throughout the year, except during spring when NO 3 deposition dominated. The total annual amount of nitrogen that was deposited to the Mpumalanga Highveld region was in the range of 6.7 kg/ha-13.1 kg/ha per year, which is well below the stipulated critical load value. Such deposition, therefore, should not pose significant threats to the natural environment on the Highveld. Between 4% and 15% of the total emitted nitrogen from power generation on the Highveld was deposited to the surface via wet and dry deposition. The remainder was advected out of the region. http://www.sajs.co.za

Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numeri... more Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numerical weather prediction models, allowing for regional and case-specific parameterisation of cloud condensation nuclei (CCN) and cloud droplet interactions. In this paper, the Thompson aerosol-aware microphysics scheme, within the Weather Research and Forecasting (WRF) model, is used for two fog cases during September 2017 over Namibia. Measurements of CCN and fog microphysics were undertaken during the AErosols, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) field campaign at Henties Bay on the coast of Namibia during September 2017. A key concept of the microphysics scheme is the conversion of water-friendly aerosols to cloud droplets (hereafter referred to as CCN activation), which could be estimated from the observations. A fog monitor 100 (FM-100) provided cloud droplet size distribution, number concentration (N t), liquid water content (LWC), and mean volumetric diameter (MVD). These measurements are used to evaluate and parameterise WRF model simulations of N t , LWC, and MVD. A sensitivity analysis was conducted through variations to the initial CCN concentration, CCN radius, and the minimum updraft speed, which are important factors that influence droplet activation in the microphysics scheme of the model. The first model scenario made use of the default settings with a constant initial CCN number concentration of 300 cm −3 and underestimated the cloud droplet number concentration, while the LWC was in good agreement with the observations. This resulted in droplet size being larger than the observations. Another scenario used modelled data as CCN initial conditions, which were an order of magnitude higher than other scenarios. However, these provided the most realistic values of N t , LWC, MVD, and droplet size distribution. From this, it was concluded that CCN activation of around 10 % in the simulations is too low, while the observed appears to be higher reaching between 20 % and 80 %, with a mean (median) of 0.55 (0.56) during fog events. To achieve this level of activation in the model, the minimum updraft speed for CCN activation was increased from 0.01 to 0.1 m s −1. This scenario provided N t , LWC, MVD, and droplet size distribution in the range of the observations, with the added benefit of a realistic initial CCN concentration. These results demonstrate the benefits of a dynamic aerosol-aware scheme when parameterised with observations.

The formation of a river of smoke crossing southern Africa was investigated during the Aerosols, ... more The formation of a river of smoke crossing southern Africa was investigated during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) campaign in September 2017. A complementary set of global and mesoscale numerical simulations as well as ground-based, airborne and space-borne observations of the dynamics, thermodynamics and composition of the atmosphere are used to characterize the river of smoke in terms of timing and vertical extent of the biomass burning aerosol (BBA) layer. The study area was under the synoptic influence of a coastal low rooted in a tropical easterly wave and a high-pressure system over the continent and westerly waves at mid latitudes, one of which had an embedded cutoff low (CoL). The coastal low interacted with the second of two approaching westerly waves and ultimately formed a mid-level tropical temperate trough (TTT). The TTT created the fast-moving air mass transported to the southwestern Indian Ocean as a river of smoke. The CoL, which developed and intensified in the upper levels associated with the first (easternmost) westerly wave, remained stationary above northern Namibia prior to the formation of the TTT and was responsible for the thickening of the BBA layer. This shows that the evolution of the river of smoke is very much tied to the evolution of the TTT, while its vertical extent is related to the presence of the CoL. The mechanisms by which the CoL, observed over Namibia in the entrance region of the river of smoke, influences the vertical structure of the BBA layer is mainly associated with the ascending motion above the BBA layer. In the presence of the CoL, the top of the BBA layer over northern Namibia reaches altitudes above 8 km. This is much higher than the average height of the top of the BBA layer over the regions where the smoke comes from (Angola, Zambia, Zimbabwe, Mozambique), which is 5 to 6 km. The results suggest that the interaction between the TTTs and the CoLs which form during the winter may have a role in promoting the transport of BBA from fire-prone regions in the tropical band to the temperate mid latitudes and the southwestern Indian Ocean.

Toxics, 2022

Emissions from residential solid fuels reduce ambient air quality and cause indoor air pollution ... more Emissions from residential solid fuels reduce ambient air quality and cause indoor air pollution resulting in adverse human health. The traditional solid fuels used for cooking include coal, straws, dung, and wood, with the latter identified as the prevalent energy source in developing countries. Emissions from such fuel sources appear to be significant hazards and risk factors for asthma and other respiratory diseases. This study aimed at reporting factors influencing the choice of dominant solid fuel for cooking and determine the emission risk from such solid fuel in three villages of Phalaborwa, Limpopo province, South Africa. The study used descriptive analysis to show the relationship between the socio-economic variables and the choice of cooking fuel at the household level. Multiple correspondence analysis (MCA) was used further to detect and represent underlying structures in the choice of dominant fuels. MCA shows the diversity and existing relationship of how variables are ...

Clean Air Journal, 2017

Satellite retrievals have highlighted the South African Highveld as a region with one of the high... more Satellite retrievals have highlighted the South African Highveld as a region with one of the highest nitrogen oxide (NOx) emission densities in the world. There are numerous sources of NOx on the Highveld, including coal-fired power stations, petrochemical and other industries, motor vehicles and lightning, but surface measurements of NOx have not indicated that there is any cause for concern. A number of research initiatives are being undertaken in an attempt to resolve the discrepancy between surface measurements and satellite retrievals of NOx. An assessment of ground-level concentrations in various environments, including industrial and urban regions, has shown that NOx levels recorded in the low-income urban area are significantly higher than those recorded downwind of industries or power stations. NO2 column densities have been remotely sensed over the Highveld using an airborne imaging Differential Optical Absorption Spectrometer (iDOAS), in order to validate the satellite re...

Atmosphere, 2021

Emissions from residential solid fuel burning in densely populated low-income settlements is a si... more Emissions from residential solid fuel burning in densely populated low-income settlements is a significant source of air pollution over the South African Highveld. The area is densely populated and highly industrialized, resulting in high concentrations of pollutants over the area. Although emissions from industrial sources are much larger, exposure to household emissions poses the most significant risk to human health. Interventions aimed at reducing solid fuel burning in low-income settlements on the Highveld have the potential to reduce exposure, but quantifying their true impact remains a challenge. We aimed to estimate the health and associated economic benefits of the regional implementation of thermal insulation as intervention measure in low-income settlements to predict the potential impact on the regional scale. We used a land use type regression model to estimate pre-intervention PM2.5 concentrations over the Highveld and then used sampled post-intervention air quality da...

Clean Air Journal, 2021

Understanding how exposure to particulate matter impacts human health is complex. Personal exposu... more Understanding how exposure to particulate matter impacts human health is complex. Personal exposure is a function of the pollution concentrations measured at any given place and time. The health impacts of this exposure are, amongst other factors, determined by how high pollutant concentrations are and what enters the body. This study considered data gathered in the winter of 2013 in a low-income community on the Mpumalanga Highveld, South Africa, which is a geographical area known for its high air pollution levels. Time-activity data collected by GPS monitors worn by individuals in the community were used to understand in which microenvironments people spend most of their time. Eight days’ worth of ambient, indoor and personal particulate matter measurements were paired with individual GPS positioning data for one study participant. We identified pollutant concentrations where the person spent time and how much particulate matter was potentially inhaled in specific micro-environmen...

We currently have a limited understanding of the spatial and temporal variability in vertically s... more We currently have a limited understanding of the spatial and temporal variability in vertically stratified atmospheric layers over Namibia and the southeast Atlantic (SEA) Ocean. Stratified layers are relevant to the transport and dilution of local and long-range transported atmospheric constituents. This study used eleven years of global positioning system radio occultation (GPS-RO) signal refractivity data (2007-2017) over Namibia and the adjacent ocean surfaces, and three years of radiosonde data from Walvis Bay, Namibia, to study the character and variability in stratified layers. From the GPS-RO data and up to a height of 10 km, we studied the spatial and temporal variability in the point of minimum gradient in refractivity, and the temperature inversion height, depth and strength. We also present the temporal variability of temperature inversions and the boundary layer height (BLH) from radiosondes. The BLH was estimated by the parcel method, the top of a surface-based inversion, the top of a stable layer identified by the bulk Richardson number (RN), and the point of minimum gradient in the refractivity (for comparison with GPS-RO data). A comparison between co-located GPS-RO to radiosonde temperature profiles found good agreement between the two, and an average underestimation of GPS-RO to radiosonde temperatures of-0.45 ± 1.25°C, with smaller differences further from the surface and with decreasing atmospheric moisture content. The minimum gradient (MG) of refractivity, calculated from these two datasets were generally in good agreement (230 ± 180 m), with an exeption of a few cases when differences exceeded 1000 m. The surface of MG across the region of interest was largely affected by macroscale circulation and changes in atmospheric moisture and cloud, and was not consistent with BLH(RN). We found correlations in the character of low-level inversions with macroscale circulation, radiation interactions with the surface, cloud cover over the ocean and the seasonal maximum in biomass burning over southern Africa. Radiative cooling on diurnal scales also affected elevated inversions between 2.5 and 10km, with more co-occurring inversions observed at night and in the morning. Elevated inversions formed most frequently over the subcontinent and under subsidence by highpressure systems in the colder months. Despite this macroscale influence peaking in the winter, the springtime inversions, like those at low levels, were strongest.

Clean Air Journal, 2014

Domestic burning activities, specifically in informal settlements, contribute greatly to the air ... more Domestic burning activities, specifically in informal settlements, contribute greatly to the air quality problems experienced by most developing urban centres. Low-income households that exist within townships in South Africa house a large portion of the South African population. These households burn vast quantities of coal, wood and other substances to provide for their energy needs. Pollutants emitted as a result of domestic burning are estimated to be one of the leading causes of respiratory illnesses in inhabitants of townships. To better understand the relationship that exists between domestic burning and the resultant pollutants, a method of quantifying these pollutants has been developed for a completely un-electrified settlement, near Johannesburg, using the quantities and type of fuel consumed. Seasonality, availability, price and cultural aspects all have a bearing on the fuel source choice and the quantity consumed. The most significant temporal observations identified f...

Clean Air Journal, 2020

The quality of air breathed in South Africa is of great concern, especially in industrialised reg... more The quality of air breathed in South Africa is of great concern, especially in industrialised regions where PM2.5 concentrations are high. Long term exposure to PM2.5 is associated with serious adverse health impacts. Traditionally, PM2.5 is monitored by a network of ground-based instruments. However, the coverage of monitoring networks in South Africa is not dense enough to fully capture the spatial variability of PM2.5 concentrations. This study explored whether satellite remote sensing could offer a viable alternative to ground-based monitoring. Using an eight-year record (2009 to 2016) of satellite retrievals (MODIS, MISR and SeaWIFS) for PM2.5 concentrations, spatial variations and temporal trends for PM2.5 are evaluated for the Vaal Triangle Airshed Priority Area (VTAPA). Results are compared to corresponding measurements from the VTAPA surface monitoring stations. High PM2.5 concentrations were clustered around the centre and towards the south-west of the VTAPA over the highl...

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, ye... more Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a 5-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three intensive observation periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June-October), aerosol particles reaching 3-5 km in altitude are transported westward over the southeast Atlantic, where they interact with one of the largest subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, as well as due to the parameterized treatment of physical processes.

South African Journal of Science, 2020

Biomass burning in Africa provides a prolific source of aerosols that are transported from the so... more Biomass burning in Africa provides a prolific source of aerosols that are transported from the source region to distant areas, as far away as South America and Australia. Models have long predicted the primary outflow and transport routes. Over time, field studies have validated the basic production and dynamics that underlie these transport patterns. In more recent years, the advancement of spaceborne active remote-sensing techniques has allowed for more detailed verification of the models and, importantly, verification of the vertical distribution of the aerosols in the transport regions, particularly with respect to westerly transport over the Atlantic Ocean. The Cloud-Aerosol Transport System (CATS) lidar on the International Space Station has detection sensitivity that provides observations that support long-held theories of aerosol transport from the African subcontinent over the remote Indian Ocean and as far downstream as Australia. Significance: Biomass burning in Africa ca...

Atmosphere, 2018

There is still a pressing concern regarding the causes of poor indoor air quality and the consequ... more There is still a pressing concern regarding the causes of poor indoor air quality and the consequent effects on health, because people spend a considerable amount of time indoors. Information about seasonal variation and the determinants of particulate matter (PM) concentrations could guide the design and implementation of intervention strategies. This study was conducted in Giyani, Limpopo province, South Africa. The main aim was to assess indoor air quality. Indoor PM and temperature were monitored to describe seasonal and diurnal patterns of indoor PM 4 concentration and to estimate the association between PM concentrations and indoor as well as ambient conditions. Indoor PM 4 was monitored hourly in kitchens for the duration of spring (September), summer (February) and winter (July). Indoor temperatures were monitored hourly in kitchens, living rooms and bedrooms. Outdoor temperature and outdoor relative humidity were also monitored for the same period. Indoor temperatures showed a large range in the three sampled seasons, with the maximum values raising the largest cause for concern. Maximum indoor temperatures in summer exceeded the threshold of 35 • C, which has been shown to have adverse health effects. Occupants of the sampled households were exposed to indoor PM 4 concentrations that exceeded national and international guidelines. Hourly indoor temperature was statistically significantly correlated to PM 4 concentrations in the summer and spring (r = 0.22 and 0.24 respectively, p < 0.001 for both) and negatively correlated to outdoor relative humidity (r = −0.27, p < 0.001). Diurnal PM 4 variations showed pronounced patterns with morning and evening peaks. PM 4 was consistently higher throughout the day in summer compared to spring and winter. Community-based intervention strategies should consider these seasonal differences in PM 4 exposure and tailor awareness messages for exposure prevention accordingly.

Clean Air Journal, 2018

Residential burning of solid fuels is a major source of fine particulate matter (PM2.5), which de... more Residential burning of solid fuels is a major source of fine particulate matter (PM2.5), which degrades indoor and ambient air quality in low-income settlements. The adverse impact of fine particulate emissions on the environment and human health is well-documented in other countries such as China and India; however, there is need for local studies to report on emission factors from residential burning of solid fuels. An emission factor quantifies the total mass of a pollutant emitted per amount of fuel burned. Emission factor is an input parameter in air quality modelling to forecast a pollutant concentrations over time and when calculating total emissions from a specific source. Local emission factors are central to managing air quality for they give results that are representative of the source compared with international emission factors. Quantifying emissions, understanding household fuel use patterns and interaction with the stove (stove operation behaviour) during a burning e...

Clean Air Journal, 2019

Coal-fired power plants are considered a major source of criteria air pollutants. The existence o... more Coal-fired power plants are considered a major source of criteria air pollutants. The existence of such activities close to densely populated areas has an impact on human health and more generally on the environment. The impact of a pollutant typically depends on its residence time and the existence of background concentration levels. This study evaluates the dispersion of PM2.5, SO2 and NOX emissions from Eskom power plants (Arnot, Hendrina, and Komati) located close to KwaZamokuhle Township. AERMOD was used to assess the contribution of each plant to the air quality of the township. This steady-state dispersion model was used to simulate surface concentrations (1-hour, 24-hour and annual average concentrations) on a 50km domain for 2015-2017. The modelled results together with data obtained from Eskom’s KwaZamokuhle monitoring site were used to estimate the extent to which these power plants contribute to the ambient air quality of KwaZamokuhle Township. The results confirm that t...

Clean Air Journal, 2019

The South African Highveld is a portion on the inland plateau characterized by low winter ambient... more The South African Highveld is a portion on the inland plateau characterized by low winter ambient temperatures. Studies done in several climatic regions around the world have found a positive relationship between inadequate housing and low indoor temperatures during the winter season. Prolonged exposure to low indoor temperature is a threat to human physical health. This study characterizes indoor human thermal comfort conditions in typical low-income residential dwellings during the winter season. Mapping indoor human thermal comfort can assist in exploring the potential for domestic thermal insulation retrofits interventions. In-situ temperature measurements were done in 2014, 2016 and 2017 across three Highveld settlements of kwaZamokuhle, kwaDela, and Jouberton. The sample included a mixture of old (pre-1994), post 1994 Reconstruction and Development Programme (RDP) as well as non-RDP structures. Findings were that 88% of sampled dwellings in Jouberton 2016, 86% in Jouberton 201...

Journal of Geophysical Research: Atmospheres, 2014

Surface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NO x = ... more Surface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NO x = NO + NO 2) and volatile organic compounds in the presence of sunlight. In this work we examine effects of the climate pattern known as the El Niño-Southern Oscillation (ENSO) and NO x variability on surface ozone from 1990 to 2007 over the South African Highveld, a heavily populated region in South Africa with numerous industrial facilities. Over summer and autumn (December-May) on the Highveld, El Niño, as signified by positive sea surface temperature (SST) anomalies over the central Pacific Ocean, is typically associated with drier and warmer than normal conditions favoring ozone formation. Conversely, La Niña, or negative SST anomalies over the central Pacific Ocean, is typically associated with cloudier and above normal rainfall conditions, hindering ozone production. We use a generalized regression model to identify any linear dependence that the Highveld ozone, measured at five air quality monitoring stations, may have on ENSO and NO x. Our results indicate that four out of the five stations exhibit a statistically significant sensitivity to ENSO at some point over the December-May period where El Niño amplifies ozone formation and La Niña reduces ozone formation. Three out of the five stations reveal statistically significant sensitivity to NO x variability, primarily in winter and spring. Accounting for ENSO and NO x effects throughout the study period of 18 years, two stations exhibit statistically significant negative ozone trends in spring, one station displays a statistically significant positive trend in August, and two stations show no statistically significant change in surface ozone. BALASHOV ET AL.

South African Journal of Science, 2011

We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South... more We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South African central industrial area, poses an environmental threat across a larger region within the dispersal footprint. A network of 37 passive monitoring sites to measure SO 2 and NO 2 was operated from August 2005 to September 2007. The area extended over the entire northern and eastern interior of South Africa. Monitoring locations were chosen to avoid direct impacts from local sources such as towns, mines and highways. Dry deposition rates of SO 2 and NO 2 were calculated from the measured concentrations. Concentrations of sulphur and nitrogen species in wet deposition from a previous study were used in conjunction with measured rainfall for the years 2006 and 2007 to estimate the wet deposition over the region. The calculated total (non-organic) acidic deposition formed the basis for an assessment of exceedance of critical loads based on sensitivity of the regional soils. Regional soil sensitivity was determined by combining two major soil attributes available in the World Inventory of Soil Emission Potentials (International Soil Reference and Information Centre). Results indicate that certain parts of the central pollution source area on the South African Highveld have the potential for critical load exceedance, while limited areas downwind show lower levels of exceedance. Areas upwind and remote areas up and downwind, including forested areas of the Drakensberg escarpment, do not show any exceedance of the critical loads.

South African Journal of Science, 2010

Atmospheric reactive nitrogen concentrations on the South African Highveld have become a growing ... more Atmospheric reactive nitrogen concentrations on the South African Highveld have become a growing concern, with satellite images indicating very high nitrogen dioxide (NO 2) concentrations in the region. This study investigated the nitrogen budget on the Highveld through the analysis of the concentration of the atmospheric nitrogen species on a temporal scale as well as the atmospheric conversion, transport and removal of these species. Data were collected at Eskom's Elandsfontein ambient air quality monitoring site, which is centrally located on the industrialised Highveld. A year's dataset from 2005 and 2006 was analysed and it was found that nitrogen oxide (NO x) concentrations were higher in winter as a result of stable atmospheric conditions, as well as prevalent westerly and north-westerly airflow, which transported emissions directly from the nearby power station sources to the monitoring site. Nitrate (NO 3) concentrations also peaked during winter, with a distinct biomass burning peak during August 2005. Diurnally, NO x concentrations indicated a tall-stack industrial source, where concentrations peaked at midday. The NO 3 concentrations were higher at night than during the day; during the day the NO 3 radical is rapidly photolysed and nitrates cannot be produced. Case studies indicated that the conversion rate of nitric oxide (NO) to NO 2 was highly variable as a result of varying atmospheric factors, which include time of day, dispersion, stability and regional atmospheric chemistry. These rates ranged from 11% to 59% per hour. Rates of dry deposition of NO, NO 2 and NO 3 were generally higher during winter as a result of higher atmospheric concentrations and increased atmospheric stability. Nitrogen was predominantly deposited as NO 2 throughout the year, except during spring when NO 3 deposition dominated. The total annual amount of nitrogen that was deposited to the Mpumalanga Highveld region was in the range of 6.7 kg/ha-13.1 kg/ha per year, which is well below the stipulated critical load value. Such deposition, therefore, should not pose significant threats to the natural environment on the Highveld. Between 4% and 15% of the total emitted nitrogen from power generation on the Highveld was deposited to the surface via wet and dry deposition. The remainder was advected out of the region. http://www.sajs.co.za