Abstract

Abstract. The evolution of organic aerosols (OAs) and their precursors in the boundary layer (BL) of the Colorado Front Range during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ, July–August 2014) was analyzed by in situ measurements and chemical transport modeling. Measurements indicated significant production of secondary OA (SOA), with enhancement ratio of OA with respect to carbon monoxide (CO) reaching 0.085±0.003 µg m−3 ppbv−1. At background mixing ratios of CO, up to ∼ 1.8 µg m−3 background OA was observed, suggesting significant non-combustion contribution to OA in the Front Range. The mean concentration of OA in plumes with a high influence of oil and natural gas (O&G) emissions was ∼ 40 % higher than in urban-influenced plumes. Positive matrix factorization (PMF) confirmed a dominant contribution of secondary, oxygenated OA (OOA) in the boundary layer instead of fresh, hydrocarbon-like OA (HOA). Combinations of primary OA (POA) volatility assumptions, aging of semi-volatile species, and different emission estimates from the O&G sector were used in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) simulation scenarios. The assumption of semi-volatile POA resulted in greater than a factor of 10 lower POA concentrations compared to PMF-resolved HOA. Including top-down modified O&G emissions resulted in substantially better agreements in modeled ethane, toluene, hydroxyl radical, and ozone compared to measurements in the high-O&G-influenced plumes. By including emissions from the O&G sector using the top-down approach, it was estimated that the O&G sector contributed to < 5 % of total OA, but up to 38 % of anthropogenic SOA (aSOA) in the region. The best agreement between the measured and simulated median OA was achieved by limiting the extent of biogenic hydrocarbon aging and consequently biogenic SOA (bSOA) production. Despite a lower production of bSOA in this scenario, contribution of bSOA to total SOA remained high at 40–54 %. Future studies aiming at a better emissions characterization of POA and intermediate-volatility organic compounds (IVOCs) from the O&G sector are valuable.

Highlights

  • Secondary organic aerosol (SOA) particles are formed from condensation of relatively low vapor pressure species in the atmosphere, generated through oxidation of volatile, semi-volatile, or intermediate-volatility organic compounds (VOCs, SVOCs, or IVOCs, respectively)

  • Data points appear to be bound by enhancement ratios of OA/ carbon monoxide (CO) = 0.016– 0.085 μg m−3 ppbv−1, with higher values observed in air masses with NOx/NOy < 0.3, i.e., air masses with a higher degree of photochemical processing, compared to fresher air masses with NOx/NOy > 0.7

  • In the absence of cyclonic flow and under similar atmospheric conditions, differences in oxygenated OA (OOA) and hydrocarbon-like OA (HOA) concentrations in urban-influenced vs. high-oil and natural gas (O&G)-influenced plumes were within the observed variabilities while mean and median concentrations of OOA were significantly higher during the Denver cyclone

Read more

Summary

Introduction

Secondary organic aerosol (SOA) particles are formed from condensation of relatively low vapor pressure species in the atmosphere, generated through oxidation of volatile, semi-volatile, or intermediate-volatility organic compounds (VOCs, SVOCs, or IVOCs, respectively). Since both biogenic and anthropogenic sources contribute to SOA precursors (Hallquist et al, 2009), SOA particles are ubiquitous in the atmosphere and contribute to a large fraction of the submicron non-refractory aerosol mass globally (Zhang et al, 2007). The impact of higher emissions of such hydrocarbons from oil and gas fields of Utah and Wyoming on wintertime ozone has been assessed through recent measurement and modeling studies (Carter and Seinfeld, 2012; Edwards et al, 2014; Rappenglück et al, 2014; Ahmadov et al, 2015)

Methods
Results
Conclusion

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.