Resolving ambient organic aerosol formation and aging pathways with simultaneous molecular composition and volatility observations
2020
Organic aerosol (OA) constitutes
a significant fraction of atmospheric
fine particle mass. However, the precursors and chemical processes
responsible for a majority of OA are rarely conclusively identified.
We use online observations of hundreds of simultaneously measured
molecular components obtained from 15 laboratory OA formation experiments
with constraints on their effective saturation vapor concentrations
to attribute the volatile organic compound (VOC) precursors and subsequent
chemical pathways giving rise to the vast majority of OA mass measured
in two forested regions. We find that precursors and chemical pathways
regulating OA composition and volatility are dynamic over hours to
days, with their variations driven by coupled interactions between
multiple oxidants. The extent of physical and photochemical aging,
and its modulation by NOx, was key to
a uniquely comprehensive combined composition–volatility description
of OA. Our findings thus provide some of the most complete mechanistic-level
guidance to the development of OA descriptions in air quality and
earth system models.
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