The influence of semi-volatile and reactive primary emissions on the abundance and properties of global organic aerosol

Abstract

Abstract.Semi-volatile and reactive primary organic aerosols are modeled on a global scale using the GISS GCM II' "unified" climate model. We employ the volatility basis set framework to simulate emissions, chemical reactions and phase partitioning of primary and secondary organic aerosol (POA and SOA). The model also incorporates the emissions and reactions of intermediate volatility organic compounds (IVOCs) as a source of organic aerosol (OA), one that has been missing in most prior work. Model predictions are evaluated against a broad set of observational constraints including mass concentrations, degree of oxygenation, volatility and isotopic composition. A traditional model that treats POA as non-volatile and non-reactive is also compared to the same set of observations to highlight the progress made in this effort. The revised model predicts a global dominance of SOA and brings the POA/SOA split into better agreement with ambient measurements. This change is due to traditionally defined POA evaporating and the evaporated vapors oxidizing to form non-traditional SOA. IVOCs (traditionally not included in chemical transport models) oxidize to form condensable products that account for a third of total OA, suggesting that global models have been missing a large source of OA. Predictions of the revised model for the SOA fraction at 17 different locations compared much better to observations than predictions from the traditional model. Modelpredicted volatility is compared with thermodenuder data collected at three different different field campaigns: FAME-2008, MILAGRO-2006 and SOAR-2005. The revised model predicts the OA volatility much more closely than the traditional model. When compared against monthly averaged OA Correspondence to: P. J. Adams (peter.adams@cmu.edu) mass concentrations measured by the IMPROVE network, predictions of the revised model lie within a factor of two in summer and mostly within a factor of five during winter. A sensitivity analysis indicates that the winter comparison can be improved either by increasing POA emissions or lowering the volatility of those emissions. Model predictions of the isotopic composition of OA are compared against those computed via a radiocarbon isotope analysis of field samples. The contemporary fraction, on average, is slightly under-predicted (20 %) during the summer months but is a factor of two lower during the winter months. We hypothesize that the large wintertime under-prediction of surface OA mass concentrations and the contemporary fraction is due to an under-representation of biofuel (particularly, residential wood burning) emissions in the emissions inventory. Overall, the model evaluation highlights the importance of treating POA as semi-volatile and reactive in order to predict accurately the sources, composition and properties of ambient OA.

Does the POA–SOA split matter for global CCN formation?

“…Traditionally, models have tended to predict a predominance of POA over SOA (Chung and Seinfeld, 2002;Kanakidou et al, 2005;Pun et al, 2003;Vutukuru et al, 2006), but measurement studies show striking evidence of SOA dominance observed at various locations, even in heavily urbanized locations (Zhang et al, 2005de Gouw et al, 2005;Volkamer et al, 2006). Recent work has suggested that many global models are underestimating OA sources (Heald et al, 2010;Spracklen et al, 2011b) that appear to be SOA, and recent improvements in SOA modeling efforts have addressed this discrepancy (Jathar et al, 2011;Pye and Seinfeld, 2010). To complicate the matter even further, different measurement techniques result in different SOA/OA fractions, as was the case for the Pittsburgh Air Quality Study, for which SOA/OA values were estimated to be 35-73 % (Subramanian et al, 2007;Cabada et al, 2004;Shrivastava et al, 2007;Zhang et al, 2005).…”

“…Traditional global models that have included SOA produced from "traditional" anthropogenic organic precursors (i.e., single compounds with well-characterized smog chamber yields such as aromatics) have predicted that these make a small contribution (about 10 %) to global OA sources (Tsigaridis and Kanakidou, 2003;Farina et al, 2010), so they are not considered here. Potentially much larger sources of anthropogenic SOA from IVOC oxidation (Jathar et al, 2011;Pye and Seinfeld, 2010) are considered in the sensitivity studies (see Sect. 2.4).…”

ORACLE 2-D (v2.0): an efficient module to compute the volatility and oxygen content of organic aerosol with a global chemistry–climate model

“…3370 A. P. : an efficient module to compute volatility and oxygen content approach, semi-volatile primary emissions, chemical aging, and SOA formation were unified within a common framework that is ideally suited for regional and global chemical modeling. Since 2006, many regional (Lane et al, 2008;Murphy and Pandis, 2009;Tsimpidi et al, , 2011Ahmadov et al, 2012;Athanasopoulou et al, 2013;Koo et al, 2014;Fountoukis et al, 2014;Ciarelli et al, 2017;Gao et al, 2017) and global (Pye and Seinfeld, 2010;Jathar et al, 2011;Jo et al, 2013;Tsimpidi et al, 2014;Hodzic et al, 2016) modeling studies have used the VBS to account for the semi-volatile nature and chemical aging of organic compounds, demonstrating improvements in reproducing the OA budget and its chemical resolution.…”

ORACLE (v1.0): module to simulate the organic aerosol composition and evolution in the atmosphere

“…This framework describes the OA absorptive partitioning, where OA is assumed to be semivolatile and photochemically reactive and is distributed in logarithmically spaced volatility bins. With this approach, the intermediate and semivolatile primary emissions and the SOA formation and its chemical aging can be simulated in a common framework that is well suited for regional and global modeling (Murphy and Pandis, 2009;Jathar et al, 2011).…”