A minimum set of ozone precursor volatile organic compounds in an urban environment

Volatile organic compounds (VOCs) were determined using the US EPA TO-15 Method in an urban area of the city of Rio de Janeiro, characterized by a high flux of light and heavy vehicles and an important contribution of biogenic sources due to the proximity of the Tijuca rainforest. Samples were collected in 2015 during four different periods corresponding to the rainy and dry seasons. Multivariate statistical analysis showed that VOC speciation was not seasonally dependent. For each sampling campaign, VOCs were classified using five different criteria: mass abundance, kinetic reactivity (according to its specific reaction coefficient with ·OH) and mechanistic reactivity (MIR, MOIR and EBIR scales). Using Venn diagrams, a minimum group of 14 compounds, which represent the complete set of 52 VOCs, was determined. This reduced group was used to simulate ozone hourly concentrations using the OZIPR box model and the SAPRC chemical mechanism. Maximum ozone values differed by 8% between the complete and minimum group, showing that this reduced group adequately describes the main process of ozone formation. The ozone maximum concentrations were correlated with the ratio of the reactivity-weighted VOCs to NOx, rather than the simple ratio of VOCs to NOx. The proposed method could be extended to other scenarios and shorten the laborious chemical determination of dozens of VOCs.