“Between 2004 and 2009, fires in southern Sumatra contributed more to particulate pollution in Singapore than fires in central Sumatra, which are located much closer,” Carly Reddington of the University of Leeds, UK, told environmentalresearchweb. “This highlights the importance of our analysis: the impact of fires on air quality depends both on the location of fires and the atmospheric transport of the smoke under the prevailing weather condition.”

Reddington believes policymakers can use the results to target fire-reduction efforts in areas that will yield the greatest benefit to air quality. Vegetation and peat fires in the region occur as a result of El Niño-induced droughts and land-use change.

“Future land-use change, under business-as-usual scenarios, involves continued expansion of oil palm plantations in…southern Kalimantan and central to southern Sumatra,” said Reddington. “Thus it is crucial to formulate sustainable land-use policy to restrict the use of fire to prepare lands for agriculture in these regions to improve air quality across southeast Asia.”

To come up with the results, Reddington and colleagues from the University of Leeds, National University of Singapore, Massachusetts Institute of Technology, US, and Malaysian Meteorological Department used observations alongside two computer models – one that simulates the whole atmosphere (GLOMAP) and one that follows the path of parcels of air arriving in Singapore (ROTRAJ).

“The locations of fires can be obtained from satellite observations, but the degree to which these fires impact air quality also depends on the amount of smoke emitted from the fires, the subsequent transport of the smoke downwind of the fire, and the eventual removal of the smoke from the atmosphere (e.g. via precipitation),” said Reddington. “A complex atmospheric model is required to simulate these processes.”

The models showed that fires in southern Sumatra account for 42–62% of fire-related PM2.5 concentrations in Singapore, with 21–35% coming from central Sumatra and 14–15% from Kalimantan.

Average 24 hour PM2.5 concentrations in Singapore vary from roughly 10 µg per cubic m up to 300 µg per cubic m on polluted days. Emissions from industry and transport also contribute; fires can add around 10 µg per cubic m to the monthly mean, the team's simulations showed.

The team’s work builds on earlier studies by using a combination of atmospheric models and observations to identify the specific fire regions in southeast Asia most responsible for air-quality degradation in Singapore and other major cities, Reddington says. “Our work also extends the time period studied to six years to give a greater understanding of the long-term average contributions of fires in southeast Asia to air-quality degradation.”

Now the team plans to investigate the impact of tropical biomass burning emissions in South America, southeast Asia and Africa on global air quality and climate. “We will continue to use a combination of atmospheric models, field and satellite observations,” said Reddington.

The team reported the findings in Environmental Research Letters (ERL).

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