Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

Abstract

Abstract. Mounting evidence from field and laboratory observations coupled with atmospheric model analyses shows that primary combustion emissions of organic compounds dynamically partition between the vapor and particulate phases, especially as near-source emissions dilute and cool to ambient conditions. The most recent version of the Community Multiscale Air Quality model version 5.2 (CMAQv5.2) accounts for the semivolatile partitioning and gas-phase aging of these primary organic aerosol (POA) compounds consistent with experimentally derived parameterizations. We also include a new surrogate species, potential secondary organic aerosol from combustion emissions (pcSOA), which provides a representation of the secondary organic aerosol (SOA) from anthropogenic combustion sources that could be missing from current chemical transport model predictions. The reasons for this missing mass likely include the following: (1) unspeciated semivolatile and intermediate volatility organic compound (SVOC and IVOC, respectively) emissions missing from current inventories, (2) multigenerational aging of organic vapor products from known SOA precursors (e.g., toluene, alkanes), (3) underestimation of SOA yields due to vapor wall losses in smog chamber experiments, and (4) reversible organic compounds-water interactions and/or aqueous-phase processing of known organic vapor emissions. CMAQ predicts the spatially averaged contribution of pcSOA to OA surface concentrations in the continental United States to be 38.6 and 23.6 % in the 2011 winter and summer, respectively.Whereas many past modeling studies focused on a particular measurement campaign, season, location, or model configuration, we endeavor to evaluate the model and important uncertain parameters with a comprehensive set of United States-based model runs using multiple horizontal scales (4 and 12 km), gas-phase chemical mechanisms, July, 2011). Model improvements manifest better correlations (e.g., the correlation coefficient at Pasadena at night increases from 0.38 to 0.62) and reductions in underprediction during the photochemically active afternoon period (e.g., bias at Pasadena from −5.62 to −2.42 µg m −3 ). Daily averaged predictions of observations at routine-monitoring networks from simulations over the continental US (CONUS) in 2011 show modest improvement during winter, with mean biases reducing from 1.14 to 0.73 µg m −3 , but less change in the summer when the decreases from POA evaporation were similar to the magnitude of added SOA mass. Because the model-performance improvement realized by including the relatively simple pcSOA approach is similar to that of more-complicated parameterizations of OA formation and aging, we recommend caution when applying these morecomplicated approaches as they currently rely on numerous uncertain parameters.The pcSOA parameters optimized for performance at the southern and northern California sites lead to higher OA formation than is observed in the CONUS evaluation. This may be due to any of the following: variations in ...

Response

“…Recent laboratory, field and model studies suggest that a significant fraction of SOA is formed in aqueous-phase cloud droplets and aerosols, following gas-phase oxidation to produce soluble species (Sorooshian et al, 2007;Fu et al, 2008;Myriokefalitakis et al, 2011;Carlton et al, 2008;Tan et al, 2012;Ervens et al, 2011;Volkamer et al, 2009). This is also consistent with the strong correlation between OA and aerosol liquid water in the southeastern US over the past decade (T. K. V. .…”

Sources and Secondary Production of Organic Aerosols in the Northeastern United States during WINTER

“…However, some of the air masses sampled contain air that has been oxidized for longer periods than in this case study. Thus, we recommend optimizing the SIMPLE parameters by performing multiple simulations in GEOS-Chem (or other 3-D models) and finding the ones that results in optimal agreement with the regional observations, similar to what was done by Murphy et al (2017), who used a different 3-D model.…”

Regional Similarities and NOx‐Related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern United States

“…CMAQ v5.1 simulations described by Pye et al (2015Pye et al ( , 2017 and Murphy et al (2017) cover the southeastern United States domain for June 2013 at 12 km by 12 km horizontal resolution using meteorology from Advanced Research Weather Research and Forecasting (WRF) model (ARW) version 3.6.1 (Pye et al, 2015. The model includes gas-phase chemistry based on SAPRC07tic with additional updates for the formation of isoprene-epoxydiol (IEPOX) SOA (Pye et al, 2015 and semivolatile organic nitrates, primarily from monoterpene reactions with nitrate radicals (Pye et al, 2015), as well as other semivolatile SOA .…”