![]() Over continents, the main precursors to SOA in the regional background are biogenic volatile organic compounds (VOC) 6 such as isoprene, monoterpenes, and sesquiterpenes. ![]() Atmospheric oxidants, such as ozone (O 3), hydroxyl radical (OH), and nitrate radical (NO 3) react with a suite of organic vapors to form an even more complex and diverse array of products, a fraction of which partition to, and/or react in, the particle phase forming secondary organic aerosol (SOA) 5. On regional and global scales, most OA is of secondary origin 4, being formed in the atmosphere via in situ chemical reactions that lead to gas-to-particle conversion of reactive organic vapors. Organic carbonaceous material is a major and often dominant component of ambient fine particle mass 3, known as organic aerosol (OA). Identifying the chemical and physical processes which regulate fine particulate mass is thus of great interest for air quality policy, public health assessments, and studies of climate sensitivity. 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.Ītmospheric fine aerosol particles affect climate through alteration of Earth’s energy balance 1 and are a major contributor to degraded air quality with strong links to premature mortality and other adverse health effects 2. The extent of physical and photochemical aging, and its modulation by NO x, were key to a uniquely comprehensive combined composition-volatility description of OA. 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. ![]() ![]() 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 VOC precursors and subsequent chemical pathways giving rise to the vast majority of OA mass measured in two forested regions. However, the precursors and chemical processes responsible for a majority of OA are rarely conclusively identified. Organic aerosol (OA) constitutes a significant fraction of atmospheric fine particle mass. ![]()
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