Aerosol mass spectrometer constraint on the global secondary organic aerosol budget

D V Spracklen,G W Mann,G Mcfiggans,K S Carslaw,M J Evans,D R Worsnop,Q Zhang,A Rap,M R Canagaratna,P Forster,J L Jimenez,H Coe,J Allan

doi:10.5194/acp-11-12109-2011

Abstract

Abstract. The budget of atmospheric secondary organic aerosol (SOA) is very uncertain, with recent estimates suggesting a global source of between 12 and 1820 Tg (SOA) a−1. We used a dataset of aerosol mass spectrometer (AMS) observations from 34 different surface locations to evaluate the GLOMAP global chemical transport model. The standard model simulation (which included SOA from monoterpenes only) underpredicted organic aerosol (OA) observed by the AMS and had little skill reproducing the variability in the dataset. We simulated SOA formation from biogenic (monoterpenes and isoprene), lumped anthropogenic and lumped biomass burning volatile organic compounds (VOCs) and varied the SOA yield from each precursor source to produce the best overall match between model and observations. We assumed that SOA is essentially non-volatile and condenses irreversibly onto existing aerosol. Our best estimate of the SOA source is 140 Tg (SOA) a−1 but with a large uncertainty range which we estimate to be 50–380 Tg (SOA) a−1. We found the minimum in normalised mean error (NME) between model and the AMS dataset when we assumed a large SOA source (100 Tg (SOA) a−1) from sources that spatially matched anthropogenic pollution (which we term antropogenically controlled SOA). We used organic carbon observations compiled by Bahadur et al. (2009) to evaluate our estimated SOA sources. We found that the model with a large anthropogenic SOA source was the most consistent with these observations, however improvement over the model with a large biogenic SOA source (250 Tg (SOA) a−1) was small. We used a dataset of 14C observations from rural locations to evaluate our estimated SOA sources. We estimated a maximum of 10 Tg (SOA) a−1 (10 %) of the anthropogenically controlled SOA source could be from fossil (urban/industrial) sources. We suggest that an additional anthropogenic source is most likely due to an anthropogenic pollution enhancement of SOA formation from biogenic VOCs. Such an anthropogenically controlled SOA source would result in substantial climate forcing. We estimated a global mean aerosol direct effect of −0.26 ± 0.15 Wm−2 and indirect (cloud albedo) effect of −0.6+0.24−0.14 Wm−2 from anthropogenically controlled SOA. The biogenic and biomass SOA sources are not well constrained with this analysis due to the limited number of OA observations in regions and periods strongly impacted by these sources. To further improve the constraints by this method, additional OA observations are needed in the tropics and the Southern Hemisphere.

Highlights

Organic aerosol (OA) contributes about 50 % of dry tropospheric submicron aerosol mass (Putaud et al, 2004; Murphy et al, 2006; Zhang et al, 2007) with important impacts on climate (Forster et al, 2007) and air quality
We have used a global dataset of organic aerosol (OA) and oxygenated organic aerosol (OOA) observed by the aerosol mass spectrometer (AMS) to evaluate the Global Model of Aerosol Processes (GLOMAP) global aerosol model
The standard GLOMAP model (Mann et al, 2010) which has secondary organic aerosol (SOA) from monoterpenes only (32 Tg (SOA) a−1), underpredicts OA (normalised mean bias (NMB)=−68 %) and OOA (NMB = −85 %) observed by the AMS and has little skill simulating the variability in the dataset (OA, normalised mean error (NME) = 74 %, root mean square error (RMSE) = 5.1 μg m−3; OOA, NME = 87 %, RMSE = 4.3 μg m−3)

Summary

Introduction

Organic aerosol (OA) contributes about 50 % of dry tropospheric submicron aerosol mass (Putaud et al, 2004; Murphy et al, 2006; Zhang et al, 2007) with important impacts on climate (Forster et al, 2007) and air quality. OA sources can be split into primary organic aerosol (POA) that is emitted directly to the atmosphere as particles, and secondary organic aerosol (SOA) that forms in the atmosphere from gasto-particle conversion. The global budget of SOA is very. Spracklen et al.: Aerosol mass spectrometer constraint on the global SOA budget uncertain. Recent top-down estimates, based either on the mass balance of volatile organic carbon (VOC) or on scaling of the sulfate budget, suggest a global source ranging from 120–1820 Tg (SOA) a−1 (Goldstein and Galbally, 2007, Hallquist et al, 2009). Atmospheric models typically use bottom-up estimates which combine emission inventories for VOCs with laboratory based SOA yields to give a global SOA formation of 12–70 Tg (SOA) a−1 (Kanakidou et al, 2005). The current uncertainty in the global SOA source (12–1820 Tg (SOA) a−1) is very substantial

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