Modeling the formation and composition of secondary organic aerosol from diesel exhaust using parameterized and semi-explicit chemistry and thermodynamic models

Abstract

Abstract. Laboratory-based studies have shown that combustion sources emit volatile organic compounds that can be photooxidized in the atmosphere to form secondary organic aerosol (SOA). In some cases, this SOA can exceed direct emissions of primary organic aerosol (POA). Jathar et al. (2017a) recently reported on experiments that used an oxidation flow reactor (OFR) to measure the photochemical production of SOA from a diesel engine operated at two different engine loads (idle, load), two fuel types (diesel, biodiesel), and two aftertreatment configurations (with and without an oxidation catalyst and particle filter). In this work, we used two different SOA models, the Volatility Basis Set (VBS) model and the Statistical Oxidation Model (SOM), to simulate the formation and composition of SOA for those experiments. Leveraging recent laboratory-based parameterizations, both frameworks accounted for a semi-volatile and reactive POA; SOA production from semi-volatile, intermediate-volatility, and volatile organic compounds (SVOC, IVOC and VOC); NOx-dependent parameterizations; multigenerational gas-phase chemistry; and kinetic gas–particle partitioning. Both frameworks demonstrated that for model predictions of SOA mass to agree with measurements across all engine load–fuel–aftertreatment combinations, it was necessary to model the kinetically limited gas–particle partitioning in OFRs and account for SOA formation from IVOCs, which were on average found to account for 70 % of the model-predicted SOA. Accounting for IVOCs, however, resulted in an average underprediction of 28 % for OA atomic O : C ratios. Model predictions of the gas-phase organic compounds (resolved in carbon and oxygen space) from the SOM compared favorably to gas-phase measurements from a chemical ionization mass spectrometer (CIMS), substantiating the semi-explicit chemistry captured by the SOM. Model–measurement comparisons were improved on using SOA parameterizations corrected for vapor wall loss. As OFRs are increasingly used to study SOA formation and evolution in laboratory and field environments, models such as those developed in this work can be used to interpret the OFR data.

A large contribution of anthropogenic organo-nitrates to secondary organic aerosol in the Alberta oil sands

“…In the high-NO x experiments, inorganic nitrate and ON were formed, with both of them generating NO + and NO + 2 fragments. Hence the inorganic and organic nitrate must be distinguished from each other, and the total N signal was determined by following the approach proposed by Farmer et al (2010;see Supplement). Ground-based observations: time series (a-d) and wind rose plots (e-i) of gas-phase species (SO 2 and NO x ), particle-phase species (organics, SO 4 , NO 3 , NH 4 and rBC) and PMF factors (HOA, LO-OOA and MO-OOA).…”

“…Extensive field investigations have demonstrated the significant formation of pON via nocturnal NO 3 radical chemistry of biogenic VOCs on a global scale (Kiendler-Scharr et al, 2016;Ng et al, 2017). Daytime production of pON has also been observed in urban and forested regions (Farmer et al, 2010;Kiendler-Scharr et al, 2016;Lee et al, 2016), but the potential role of anthropogenic VOCs in pON formation remains largely unexplored. Recently, a field study demonstrated that oil and natural gas drilling operations were associated with alkanederived pON production (L. .…”

“…a calibration standard) can be used an indicator as substantial contribution of ON in the observed organic aerosol. The mass concentrations of pON and inorganic nitrate (NO − 3 ) can be estimated based on the observed NO + /NO + 2 ratio, assuming that the molecular weight and NO + /NO + 2 ratio of ON are 200-300 g mol −1 and 5-10, respectively, based on the method previously described in Farmer et al (2010) and Xu et al (2015). The details (i.e.…”

A Large Contribution of Anthropogenic Organo-Nitrates to Secondary Organic Aerosol in the Alberta Oil Sands

“…SOA production (Eluri et al, 2017) and global SOA budgets (Hodzic et al, 2016). Our findings highlight the important role of daytime pON formation for SOA production in urban and industrial regions with strong emissions of anthropogenic IVOCs and NOx (e.g.…”

“…Zhao et al, 2015). Including IVOCs in SOA prediction models can have great impact on estimating the production of anthropogenic SOA in urban environments and global SOA budgets (Eluri et al, 2017;Hodzic et al, 2016). However, anthropogenic pON formation chemistry has not been fully integrated into current SOA prediction models.…”