Science. “Volatile Chemical Products Emerging as Largest Petrochemical Source of Urban Organic Emission,” McDonald et. al., February 16, 2018. Science 16 Feb 2018: Vol. 359, Issue 6377, pp. 760-76.
From the Human Health Implications section:
“Although fossil fuels remain important sources of urban air pollution, exposure to ambient PM2.5 is increasingly from chemical products as the transportation sector becomes cleaner. Additionally, because a large fraction of VCP emissions occurs in buildings, exposure to air toxics is of concern indoors (59). Below we summarize two implications for human health:
(1) The average fossil contribution to carbonaceous aerosols (∑ = black carbon + organic aerosol) measured in ambient air at Pasadena was 3.4 ± 1.0 μg m−3 (55, 56), which does not include nonfossil components from cooking or biogenic sources. Of the fossil total, ~40%, or ~1.3 μg m−3, is attributed to directly emitted particles (55, 56), mainly from diesel engines (7). The SOA from use of VCPs (Fig. 4D) is of similar magnitude and accounts for ~35% of the fossil total, or ~1.2 μg m−3. As diesel particle filters and oxidation catalysts become more widespread, and reduce diesel contributions to PM2.5 (60), the fraction of PM2.5 from VCPs will grow because SOA precursor emissions from VCPs are not decreasing as quickly (7).
(2) We show that indoor emissions of aromatics and chlorinated hydrocarbons from use of VCPs are consistent with typical indoor concentrations (Fig. 3D), which are of concern because of their human toxicity (61). Indoor emissions of aromatic compounds have decreased by ~7% per year between 1981 and 2001 (33), comparable to decreases in transportation emissions of ~8% per year (7, 22). Consumer uses of VCPs likely remain key sources of human exposure to air toxics relative to fossil fuels, especially because people spend most of their time indoors (62).
Traditional approaches to mitigating air pollution emphasize transportation and industrial sources (63). However, chemical products are an emerging source of urban VOCs (22), including SOA precursors (7), because VOC emissions from VCPs are not declining as fast as those from transportation. New paradigms leveraging research tools from the indoor and outdoor air quality communities could strengthen efforts to reduce human exposure to O3, PM2.5, and air toxics. As the composition of chemical products has evolved to remove chlorofluorocarbons to address stratospheric O3, shifted from solvent- to water-borne formulations to mitigate tropospheric O3, and phased out toxic components (33), VCPs have begun to contribute significantly to SOA formation outdoors. Given that global mortality from fine particles is significantly greater than for ambient O3 pollution (1), further study is needed on whether chemical products currently designed to mitigate O3 are also sufficient to protect humans from exposure to fine particles.”