Observations confirm that volatile chemical products are the main source of petrochemical emissions in US cities

Although air pollution has been declining for decades, urban areas in the United States are still affected by excessive ozone in summer and particulate matter in winter. Volatile organic compounds (VOCs) are known precursors of secondary organic aerosols (SOAs) and photochemically produced ozone. Through successful regulatory measures, urban sources of VOC emissions, including road transport emissions, have been significantly reduced over the past few decades. The dramatic reduction in VOC emissions has led to a change in the distribution of urban emissions and non-combustion VOC sources, such as volatile chemical products, which now account for a higher proportion of the urban VOC burden. Given this variation in emission sources, it is critical to quantify the relative contribution of VCP and mobile source emissions to urban pollution. Here, ground field and mobile laboratory measurements of volatile organic compounds were carried out. Two ground sites with different population densities, Boulder, Colorado, and New York City, were selected to assess the effects of VCP in cities with different blends of VCP and mobile source emissions. Positive matrix factorization is used to attribute hundreds of compounds to mobile and VCP-dominated sources. In Boulder and New York City, VCP-led emissions accounted for 42 percent and 78 percent of anthropogenic VOC emissions, respectively, while mobile sources accounted for 58 percent and 22 percent. The allocated VOC emissions were compared with those estimated in the fuel-based vehicle emission inventory and VCP, and it was agreed to make a batch comparison of up to 25% and a comparison of more than half of the individual compounds of up to 30%. The list of assessed VOCs extends to other U.S. cities, showing that 50 to 80 percent of urban anthropogenic VOC emissions, reactivity, and SOA formation potential are associated with VCP-led sources, indicating their important role in U.S. urban air quality.

Many volatile organic compounds (VOCs) are classified as possible or known airborne toxicity, human carcinogens, and irritants, and have been linked to asthma and other respiratory diseases. In addition, VOCs are precursors to the formation of secondary organic aerosols and tropospheric ozone. Historically, transportation as well as industrial processes and energy production have been responsible for most VOCs measured in outdoor urban environments in certain cities. However, decades of successful control of VOC emissions, such as the reduction of motor vehicles, have shifted the distribution of urban emissions towards non-motor sources. Therefore, volatile chemical products (VCPs) have become the largest source of petrochemical VOC emissions in Los Angeles (LA) and New York City (NYC).