The emission of volatile chemical products (VCPs) may contribute as much as half the total VOC emissions from ‘fossil’ petrochemical sources in western cities, according to a recent study led by the National Oceanic and Atmospheric Administration (NOAA), USA. This in turn could mean that regional ozone and aerosol burdens are increasingly driven by the emissions of these precursors, as production of primary and secondary aerosols from transport sources is reduced by improved regulation and technology.

This is partly attributed to the use of VCPs in paints, household cleaning and fragrance products, many of which are designed to evaporate and hence a higher proportion is emitted as volatile compounds rather than burned as fuel. Although indoor levels of VOCs in Los Angeles were 10 times higher than outdoors, these indoor sources exfiltrate and contribute significantly to the outdoor concentrations and hence to secondary organic aerosol formation – the 5% (by mass) share of petrochemical product use in VCP products (compared with 95% as diesel, gasoline and natural gas) may translate to over 60% of the SOA potential from petrochemical sources.

The study highlights the importance of considering non-traffic sources of aerosol precursors, but should not detract from the necessity to continue to reduce emissions from traffic.