Thursday, November 28, 2013

Measuring and Characterizing Particulate Pollution in Accra, Ghana (ERL)

Cities in the developing world often suffer poor air quality, which can be hazardous to health, yet there have been relatively few studies. With that in mind, a team has assessed the particles causing air pollution in rich and poor neighbourhoods of Ghana’s capital Accra.

Link to the press release.
Link to the journal article in ERL.

"Sub-Saharan African cities are increasingly among the most polluted cities in the world," Zheng Zhou of Harvard School of Public Health, US, told environmentalresearchweb. "However, the availability of air pollution data in this region is limited. Most current studies have focused on the indoor environment in the rural area; substantially less work has been done in the urban area."

Accra, which had a population of 2.27 million in 2012, is one of Africa’s fastest growing cities. Zhou and colleagues from Brazil, the US, Ghana and the UK took particulate matter samples in four neighbourhoods of the capital between September 2007 and August 2008. The areas – James Town/Usher Town, Asylum Down, Nima and East Legon – lay on a straight line from the coast to Accra’s northern boundary.
James Town/Usher Town and Nima are densely populated, low-income areas where most people use biomass for cooking at home and for street food. Asylum Down is a middle-class area and East Legon is an upper-class district where most families live on large plots of land in modern low-rise homes, according to the researchers.

Study neighbourhoods and measurement sites. The polygons on the central panel show census enumeration areas (EAs). Each EA has approximately the same population; hence the area of an EA is inversely related to population density. EAs are categorized according to quintile in terms of per cent of household using biomass fuels. Each colour represents a different quintile. The sites were at locations that were typical of each neighbourhood's living environment, with the EL site being far from major traffic and the AD site being next to a road with moderate traffic. In NM we also had a second site next to a road with heavy traffic. The distances of measurement sites to the ocean coast were: JT 0.5 km, AD 3 km, NM 4.5 km, and EL 9 km.
Biomass combustion was responsible for between 10.6 and 21.3 µg/m3 of fine particle mass, contributing more in the poorest neighbourhood, the team found. Other particles came from sea salt, vehicle emissions, tire and brake wear, road dust, and burning of solid waste. As for biomass combustion, burning of solid waste was a greater source of pollution in poorer areas, where waste is collected less frequently. At the measurement stations near traffic routes, in Asylum Down and Nima, there were more road dust and traffic aerosols.
"We have seen large contributions from biomass burning to PM2.5 levels – particulate matter less than 2.5 micrometers in size – in urban Accra," said Zhou. "On average, biomass combustion contributed 40 to 50% of total PM2.5 mass outside the windy and dusty Harmattan period. Road dust and vehicle emission also accounted for 10 to 30% of total PM2.5 mass. We found that contributions from sea salt and crustal dust varied significantly by season."

Between December and January, the Harmattan, a dry and dusty West African trade wind, blows from the Sahara south towards the ocean in the Gulf of Guinea. "During peak Harmattan season, crustal dust was the largest contributor to PM, accounting for about 40% of total PM mass," said Zhou. The period saw about 10 times as much particle mass from crustal sources as usual, as well as an increase in resuspended road dust and particles from biomass burning.

"Our results show that urban air pollution in Accra is a complex mixture of both natural and anthropogenic sources," said Zhou. "Urban air quality in African cities can benefit from reducing dependence on solid fuels and improving road conditions. [This] requires policies related to energy, transportation and urban planning, and forestry and agriculture, with explicit attention paid to the impacts of each strategy in poor communities. Such cross-sectoral integration requires emphasis on the urban environment and urban poverty in the post-2015 development agenda."

For example, as the team writes in Environmental Research Letters (ERL), large-scale transitions to cleaner fuels such as liquefied petroleum gas (LPG) may require targeted subsidies for fuel, and financial assistance towards the initial cost of an LPG stove for poor households. "Perhaps more importantly, sustained use of clean fuels requires improving the energy delivery and distribution infrastructure so that people can have regular trouble-free access to fuel purchase, something currently not available in poor neighbourhoods," the researchers added.

There’s also a need for research on the acute and chronic health effects of exposure to crustal particles, the team believes, and whether air pollution regulations in developing countries should be based on total particle mass or specifically target combustion sources.

"We hope to pursue studies that quantify the health effects of air pollution in Accra, noting its different chemical composition and sources," said Zhou. "We would also like to continuously examine whether energy and environmental policies are influencing air pollution, either as improvement or deterioration."

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