Simulating secondary organic aerosol from missing diesel-related intermediate-volatility organic compound emissions during the Clean Air for London (ClearfLo) campaign

Abstract

Abstract. We present high-resolution (5 km × 5 km) atmospheric chemical transport model (ACTM) simulations of the impact of newly estimated traffic-related emissions on secondary organic aerosol (SOA) formation over the UK for 2012. Our simulations include additional diesel-related intermediate-volatility organic compound (IVOC) emissions derived directly from comprehensive field measurements at an urban background site in London during the 2012 Clean Air for London (ClearfLo) campaign. Our IVOC emissions are added proportionally to VOC emissions, as opposed to proportionally to primary organic aerosol (POA) as has been done by previous ACTM studies seeking to simulate the effects of these missing emissions. Modelled concentrations are evaluated against hourly and daily measurements of organic aerosol (OA) components derived from aerosol mass spectrometer (AMS) measurements also made during the ClearfLo campaign at three sites in the London area. According to the model simulations, diesel-related IVOCs can explain on average ∼ 30 % of the annual SOA in and around London. Furthermore, the 90th percentile of modelled daily SOA concentrations for the whole year is 3.8 µg m −3 , constituting a notable addition to total particulate matter. More measurements of these precursors (currently not included in official emissions inventories) is recommended. During the period of concurrent measurements, SOA concentrations at the Detling rural background location east of London were greater than at the central London location. The model shows that this was caused by an intense pollution plume with aPublished by Copernicus Publications on behalf of the European Geosciences Union. 6454 R. Ots et al.: Simulating SOA from missing diesel-related IVOC emissions in London strong gradient of imported SOA passing over the rural location. This demonstrates the value of modelling for supporting the interpretation of measurements taken at different sites or for short durations.

Air quality simulations for London using a coupled regional-to-local modelling system

“…This WRF configuration is similar to that discussed in Vieno et al (2010), where it is shown to perform well in comparison with measurements. An evaluation of the WRF-EMEP4UK modelling system against measured gaseous and particulate pollutant concentrations across the UK for 2001 to 2010 is given by Lin et al (2017), while Ots et al (2016) compares WRF-EMEP4UK air quality simulations with detailed measurements of secondary organic aerosols made in London during the 2012 ClearfLo campaign.…”

“…The gaseous chemical scheme used in EMEP4UK in this study is the CRI-v2-R5 mechanism (Watson et al, 2008), which has 220 species and 609 reactions. Five classes of fine and coarse particles, with differing size and deposition properties, are used in EMEP4UK along with the MARS (Model for an Aerosol Reacting System) equilibrium module for gas-aerosol partitioning of secondary inorganic aerosol (Binkowski and Shankar, 1995;Simpson et al, 2012) and a treatment of secondary organic aerosol formation using the volatility basis set approach Ots et al, 2016). Dry (including stomatal) and wet deposition of gases and particles are simulated.…”

Modelling carbonaceous aerosol from residential solid fuel burning with different assumptions for emissions

“…The performance of this version of the EMEP4UK model simulating a standard suite of gas-phase components and secondary inorganic aerosol PM components is reported in Ots et al (2016a) comparing with a full year of measurements in London in 2012. In brief, Ots et al (2016a) reported an NMB of −1% and r = 0.79 for ozone, an NMB of −32% and r = 0.78 for NO x , Table 1.…”

“…In brief, Ots et al (2016a) reported an NMB of −1% and r = 0.79 for ozone, an NMB of −32% and r = 0.78 for NO x , Table 1. SNAP source sectors as specified in the emissions input to the model (CEIP, 2015).…”

“…Model-measurement comparisons of a range of gaseous and particulate pollutants (Ots et al, 2016a) show that modelled concentrations of SFOA at the North Kensington site in London are substantially underestimated (normalised mean bias, NMB, 5 of −71%) compared to an annual dataset of PMF apportionment of AMS measurements collected during the 2012 Clean Air for London campaign (ClearfLo; Bohnenstengel et al (2014); Young et al (2015a); Xu et al (2016)). The aim of this work is to use these measurements of SFOA as the basis for an atmospheric chemical transport model exploration of potential closure of this discrepancy.…”