The composition and variability of atmospheric aerosol over Southeast Asia during 2008

Abstract

Abstract. We use a nested version of the GEOS-Chem global 3-D chemistry transport model to better understand the composition and variation of aerosol over Borneo and the broader Southeast Asian region in conjunction with aircraft and satellite observations. Our focus on Southeast Asia reflects the importance of this region as a source of reactive organic gases and aerosols from natural forests, biomass burning, and food and fuel crops. We particularly focus on July 2008 when the UK BAe-146 research aircraft was deployed over northern Malaysian Borneo as part of the ACES/OP3 measurement campaign. During July 2008 we find using the model that Borneo (defined as Borneo Island and the surrounding Indonesian islands) was a net exporter of primary organic aerosol (42 kT) and black carbon aerosol (11 kT). We find only 13 % of volatile organic compound oxidation products partition to secondary organic aerosol (SOA), with Borneo being a net exporter of SOA (15 kT). SOA represents approximately 19 % of the total organic aerosol over the region. Sulphate is mainly from aqueous-phase oxidation (68 %), with smaller contributions from gas-phase oxidation (15 %) and advection into the regions (14 %). We find that there is a large source of sea salt, as expected, but this largely deposits within the region; we find that dust aerosol plays only a relatively small role in the aerosol burden. In contrast to coincident surface measurements over Northern Borneo that find a pristine environment with evidence for substantial biogenic SOA formation we find that the free troposphere is influenced by biomass burning aerosol transported from the northwest of the Island and further afield. We find several transport events during July 2008 over Borneo associated with elevated aerosol concentrations, none of which coincide with the aircraft flights. We use MODIS aerosol optical depths (AOD) data and the model to put the July campaign into a longer temporal perspective. We find that Borneo is where the model has the least skill at reproducing the data, where the model has a negative bias of 76 % and only captures 14 % of the observed variability. This model performance reflects the small-scale island-marine environment and the mix of aerosol species, with the model showing more skill at reproducing observed AOD over larger continental regions such as China where AOD is dominated by one aerosol type. The model shows that AOD over Borneo is approximately evenly split between organic and sulphate aerosol with sea salt representing 10-20 % during May-September; we find a similar breakdown over continental Southeast Asia but with less sea salt aerosol and more dust aerosol. In contrast, East China AOD is determined mainly by sulphate aerosol and a seasonal source of dust aerosol, as expected. Realistic sensitivity runs, designed to test our underlying assumptions about emissions and chemistry over Borneo, show that model AOD is most sensitive to isoprene emissions and organic gas-phase partitioning but all fail to improve significantly upon the co...

Burden of Disease from Rising Coal-Fired Power Plant Emissions in Southeast Asia

“…The GEOS-Chem simulation is conducted at the native resolution over East Asia and adjacent oceans (11S-55 N, 70–150 E), , nested within a global simulation at 2° × 2.5° resolution that provides dynamic boundary conditions. This East Asian nested version of GEOS-Chem has been extensively evaluated for China with observations of aerosols − and ozone. − Evaluations have also been performed for Southeast Asia, , but observations are more limited in that region.…”

Application of spectral analysis techniques to the intercomparison of aerosol data – Part 4: Synthesized analysis of multisensor satellite and ground-based AOD measurements using combined maximum covariance analysis

“…Therefore, places where retrieval skills are low often correspond to those where model fields are inaccurate. For example, Trivitayanurak et al (2012) found poor agreement between the GEOS (Goddard Earth Observing System)-Chem simulated AOD and MODIS AOD for the southeastern Asia region due to the uncertainties in satellite retrieval. The CMCA technique will identify these regions, and thus provide insights into the problems in either the satellite, the model or both.…”

“…Again no qualified AERONET station is available here. As this region is a major biomass-burning source region (Generoso et al, 2003;van der Werf et al, 2006), it should also be the focus of future AERONET instrumentation deployment. A few AERONET stations have already been established and have begun acquiring data in recent years, and a more complete study of the seasonal and interannual variability of this region will become possible in the future.…”

Impacts of current and projected oil palm plantation expansion on air quality over Southeast Asia

“…Global emissions from aviation are based on the AEIC inventory (Stettler et al, 2011;Simone et al, 2012). Biomass burning emissions for 2006 follow the GFED3 inventory (van der Werf et al, 2010). We note that the GFED3 emissions indicate that 2006 was a higher than average fire year in the region.…”

“…Trivitayanurak et al (2012) use the nested model to better understand the distribution and sources of atmospheric trace constituents over Asia. They find that the model captures the vertical and spatial variability of trace constituents such as CO, isoprene, and sulfate to within 30 % of observations from several aircraft campaigns.…”