Source-resolved attribution of ground-level ozone formation potential from VOC emissions in Metropolitan Vancouver, BC.

The common regulatory approach for managing ground-level ozone (O) formation is based upon reducing the emission of total VOC in VOC limited regions, and the emission of NO in NO limited regions. However, the characteristic VOC species emitted from different sources are of different ozone formation potentials (OFP). Without an in-depth understanding of the relative OFP contributions from specific sources, the effectiveness of the existing approach for controlling ground-level O at the regional scale is limited. This study collected and analyzed five years (2012-2016) of monitoring data for 56 most photochemically reactive VOC species at Port Moody, an industrial city in Metro Vancouver, Canada that has experienced elevated O levels in its ambience. Source-specific contributions to OFP were quantified for major VOC emitters to deliberate the underlying causes of elevated O recently observed in this populated region. Six sources were identified using the positive matrix factorization (PMF) model, consisting of fuel production and combustion, fuel evaporation, vehicle exhaust, industrial coatings/solvents, petrochemical source, and other industrial emission. Although the top three contributors to total VOCs are fuel production and combustion (34.5%), fuel evaporation (21.4%), and vehicle exhaust (20.6%), the top three contributors to OFP are fuel production and combustion (27.1%), vehicle exhaust (23.7%), and industrial coatings/solvents (17.2%). Additionally, potential source contribution function (PSCF) analysis was conducted to generate the geographical distribution of VOC and OFP sources in different seasons. The results revealed that, in the Metro Vancouver area, the OFP hotspots have been significantly different from the VOC emission hotspots. In general, regional sources, especially those located in the northeastern direction of Metro Vancouver, have greater influence on the VOCs levels. However, OFP has been predominantly affected by transportation and industrial sources at the local scale. Therefore, to formulate effective strategies for reducing ground-level O, the seasonal and spatial variations of major OFP sources should be assessed by the regulatory authorities.