Investigation of the Atmospheric Impacts and Ozone Formation Potentials of Styrene

Environmental chamber experiments and computer model calculations were conducted to assess the impacts of the gas-phase reactions of styrene on the atmospheric formation of ozone and styrene's known oxidation products. The experiments consisted of determining the effects of adding styrene on ozone formation, NO oxidation, integrated OH radical levels, and formation of benzaldehyde, formaldehyde, and peroxybenzoyl nitrate (PBzN) in various simulated photochemical smog systems in a dual ~2500-liter, xenon-arc-irradiated Teflon environmental chamber. The gas-phase mechanism for the atmospheric reactions of styrene was updated based on available literature data, and model predictions using the mechanism were compared with the results of the chamber experiments. The model predictions were consistent with the observed effects of styrene on benzaldehyde and formaldehyde and not inconsistent with the qualitative PBzN data, but the effect of styrene on radical levels and ozone could only be simulated if it was assumed that the reaction of styrene with ozone does not result in radical formation. The mechanisms which fit the chamber data was used to used to predict the impacts of styrene on ozone formation under various atmospheric conditions. The changes to the ozone + styrene mechanism caused the Maximum Incremental Reactivity (MIR) for styrene, relative to the average of all VOC emissions, to decrease from ~0.7 to ~0.6, on a mass basis. Uncertainties in the mechanism for the styrene + NO reactions were found not to significantly impact 3 ambient ozone impact predictions. The impact of styrene on ozone formation depended significantly on NO x conditions, being greater than that of ethane (but less than the average of all emissions on a mass basis and therefore not " highly reactive ") under the high NO conditions of the MIR scale, but becoming significantly x negative in scenarios with lower NO levels. The reactivities in the MIR scenarios were the same regardless x of whether the ozone impact was defined in terms of peak ozone or the maximum 8-hour average, but the 8-hour average ozone reactivities declined much more slowly as NO was reduced than reactivities in terms of x effects on peak ozone yields. It is concluded that models with an appropriate styrene mechanism (and an explicit representation of benzaldehyde) can probably reliably represent the effects of styrene on the formation of ozone, benzaldehyde, formaldehyde, PBzN, and overall radical levels in the atmosphere. However, the known products from styrene's reactions account for only ~60% of the carbon …