Quantifying the Contribution from Volatile Chemical Product Emissions to Ozone Formation in Los Angeles, California

Abstract:

Analysis of volatile organic compound (VOC) data from the CalNex study in 2010 indicated that the dominant fraction of emissions is no longer attributed to transportation fuels but rather to evaporative emissions associated with the use of volatile chemical products (VCPs), such as cleaning and personal care products, paints, inks, glues, solvents and pesticides. A large part of these emissions occurs inside buildings. The VOC composition of these emerging atmospheric sources is rich in functionalized species (alcohols, ketones, glycols, ethers, etc.) and quite different from that of hydrocarbon-rich fuels. This brings up the question how efficient the emissions from VCPs are in the formation of ozone. In this work, we have modeled ozone chemistry during CalNex 2010 using the Master Chemical Mechanism (MCM) version 3.3.1 and a detailed representation of VOC emissions based on measurements complemented with inventory estimates. Our model calculations show that VCP emissions are responsible for significant ozone formation. In addition to the MCM, we also modeled ozone using two lumped models with a simplified representation of emissions and chemistry and found that the Regional Atmospheric Chemistry Mechanism (RACM version 2) performed much better in terms of ozone formation than the Carbon Bond Mechanism (CB version 6). Since 2010, emissions of nitrogen oxides and VOCs have decreased in Los Angeles, but ozone did not decrease significantly as a result. Using MCM, we reproduce these trends in ozone based on inventoried and measured emissions trends in nitrogen oxides and VOCs, with the important assumption that VCP emissions have not changed over the past decade. Finally, we studied the weekend-weekday effect in ozone formation and found that the model reproduces an increasing trend in weekday ozone, but a much weaker trend in weekend ozone.