Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

/pdf/bounding-the-role-of-black-carbon-in-the-climate-system-a-1fc3novd9r.pdf

Bounding the role of black carbon in the climate system: A scientific assessment

Africa is blessed with natural and mineral resources, but exploitation of these resources has led to extreme pollution of the environment. Population growth and urbanization due to developments have also contributed immensely to the current pollution in Africa. Traffic emissions, transported dust and open burning are all significant contributors to air pollution in Africa. The Sahara desert is a major source of transported dust, especially during the harmattan season in West Africa. Mercury emissions are very high in South Africa due to coal combustion and gold mining. Air pollutants may contaminate water and soil through atmospheric deposition. However, the major pollution sources for surface waters are the urban and industrial discharges of untreated effluents into the water. A few African countries have standards for effluent discharge into surface waters, but it is unknown whether these standards are being enforced. Though groundwater sources in wells and boreholes are the major sources of drinking water for the African populace, the biological water quality of these groundwater sources is mostly low in the region due to close proximity to sanitary facilities. Identified sources of soil pollution in Africa include agricultural activities, mining, roadside emissions, auto-mechanic workshops, refuse dumps and e-waste. Oil spills are a major problem in oil-rich African countries such as Nigeria and Angola. Agricultural activities are the lowest impacting the soil in Africa, while e-waste recycling was the highest with Pb, Cu and Zn at extremely high concentrations (>1%). There is a need for proper regulation of environmental pollutants in Africa.

Environmental pollution in Africa

Rapid urban population growth, air pollution emissions, and changing patterns of disease in African cities may increase the burden of air pollution-related morbidity and mortality in coming decades. Yet, air monitoring is limited across the continent and many countries lack air quality standards. This paper focuses on particulate matter (PM) pollution, one of the most relevant and widely used indicators of urban air quality. We provide an overview of published PM monitoring studies in Africa, outline major themes, point out data gaps, and discuss strategies for addressing particulate air pollution in rapidly growing African cities. Our review reveals that, although few studies have reported annual mean levels of coarse and fine particles, collective evidence from short- and long-term air monitoring studies across urban Africa demonstrates that pollution levels often exceed international guidelines. Furthermore, pollution levels may be rising as a result of increased motor vehicle traffic building on already high background concentrations of PM in many locations due to climatic and geographic conditions. Biomass burning and industrial activities, often located in cities, further exacerbate levels of PM. Despite the health risks this situation presents, air quality programs, particularly in sub-Saharan Africa, have been stalled or discontinued in recent years. Implementation of systematic PM data collection would enable air pollution-related health impact assessments, the development of strategies to reduce the air pollution health burden, and facilitate urban planning and transportation policy as it relates to air quality and health.

/pdf/particulate-matter-pollution-in-african-cities-4iagedckde.pdf

Particulate matter pollution in African cities

Epidemiologic studies have consistently reported associations between outdoor fine particulate matter (PM2.5) air pollution and adverse health effects. Although Asia bears the majority of the public health burden from air pollution, few epidemiologic studies have been conducted outside of North America and Europe due in part to challenges in population exposure assessment. We assessed the feasibility of two current exposure assessment techniques, land use regression (LUR) modeling and mobile monitoring, and estimated the mortality attributable to air pollution in Ulaanbaatar, Mongolia. We developed LUR models for predicting wintertime spatial patterns of NO2 and SO2 based on 2-week passive Ogawa measurements at 37 locations and freely available geographic predictors. The models explained 74% and 78% of the variance in NO2 and SO2, respectively. Land cover characteristics derived from satellite images were useful predictors of both pollutants. Mobile PM2.5 monitoring with an integrating nephelometer also showed promise, capturing substantial spatial variation in PM2.5 concentrations. The spatial patterns in SO2 and PM, seasonal and diurnal patterns in PM2.5, and high wintertime PM2.5/PM10 ratios were consistent with a major impact from coal and wood combustion in the city’s low-income traditional housing (ger) areas. The annual average concentration of PM2.5 measured at a centrally located government monitoring site was 75 μg/m3 or more than seven times the World Health Organization’s PM2.5 air quality guideline, driven by a wintertime average concentration of 148 μg/m3. PM2.5 concentrations measured in a traditional housing area were higher, with a wintertime mean PM2.5 concentration of 250 μg/m3. We conservatively estimated that 29% (95% CI, 12–43%) of cardiopulmonary deaths and 40% (95% CI, 17–56%) of lung cancer deaths in the city are attributable to outdoor air pollution. These deaths correspond to nearly 10% of the city’s total mortality, with estimates ranging to more than 13% of mortality under less conservative model assumptions. LUR models and mobile monitoring can be successfully implemented in developing country cities, thus cost-effectively improving exposure assessment for epidemiology and risk assessment. Air pollution represents a major threat to public health in Ulaanbaatar, Mongolia, and reducing home heating emissions in traditional housing areas should be the primary focus of air pollution control efforts.

/pdf/an-assessment-of-air-pollution-and-its-attributable-3r3h34etod.pdf

An assessment of air pollution and its attributable mortality in Ulaanbaatar, Mongolia.

https://core.ac.uk/download/pdf/6776674.pdf

Clean fuel-saving technology adoption in urban Ethiopia

Results from a pilot-scale air quality study in Addis Ababa, Ethiopia

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Results from a pilot-scale air quality study in Addis Ababa, Ethiopia