Aerosol mass spectrometer constraint on the global secondary organic aerosol budget

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 observaCorrespondence to: D. V. Spracklen (dominick@env.leeds.ac.uk) tions, however improvement over the model with a large biogenic SOA source (250 Tg (SOA) a −1 ) was small. We used a dataset of 14 C 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.

Semi-empirical parameterization of size-dependent atmospheric nanoparticle growth in continental environments

“…The aerosol constituents formed through these oxidation reactions and their subsequent condensation to the particulate phase are called secondary organic aerosol (SOA). Traditionally biogenic VOCs (BVOC), such as monoterpenes (MT) and isoprene, are thought to be the dominant source of atmospheric SOA (e.g., Kanakidou et al, 2005;Hallquist et al, 2009), but recent studies suggest also a notable anthropogenic contribution to SOA formation (Volkamer et al, 2006;Zhang et al, 2007;Heald et al, 2011;Hoyle et a., 2011;Spracklen et al, 2011).…”

“…Schematic of processes leading to nanoparticle growth from the perspective of the parameterization: formation of SORG MT , SORG bg and sulfuric acid from biogenic volatile organic compounds (BVOCs) and anthropogenic pollution via atmospheric oxidation and condensation of these vapors onto nanoparticles. Model simulations with GEOS-Chem-TOMAS (Pierce et al, 2013) show that SORG bg can be linked to the products of oxidation of biogenic organics in the presence of anthropogenic pollutants (Hoyle et al, 2011;Spracklen et al, 2011). particle growth. The parameterization is aimed to be simple and thus easily applicable in large-scale atmospheric models.…”

Ideas and perspectives: on the emission of amines from terrestrial vegetation in the context of new atmospheric particle formation

“…Estimates of the global secondary aerosol budget are highly uncertain due to uncertainties in gas-phase precursor contributions to NPF and limited mechanistic comprehension (Spracklen et al, 2011). While NPF rates observed in the field do not comply with the classical process understanding involving sulfuric acid (SA) and water (Kirkby et al, 2011;Chen et al, 2012), it has recently become increasingly clear that the ternary system of SA and water, together with neutralising compounds like ammonia (NH 3 ) or amines, is a key system in NPF (Chen et al, 2012;Almeida et al, 2013;Kurten et al, 2014).…”

Improving the simulation of global aerosol with size-segregated anthropogenic number emissions

“…Aerosol particles and their precursor vapors are being emitted from both biogenic and anthropogenic sources, in addition to which they may also result from interactions between biogenic and anthropogenic emissions (Spracklen et al, 2011;Shilling et al, 2013). The increasing number concentration of accumulation mode particles decreases the formation and growth of smaller particles by increasing the sink for condensing vapor molecules, termed the condensation sink (CS, Kulmala et al, 2001), and by increasing the coagulation sink for small freshly-formed particles.…”