Organic Aerosol Composition and Sources

Organic aerosols are a complex and dynamic subset of atmospheric particulate matter, comprising a vast array of carbon-containing molecules that originate from both direct emissions and in-cloud or gas-phase chemical reactions. Primary organic aerosols enter the atmosphere through combustion processes such as vehicle exhaust, biomass burning and industrial activities, as well as through biological emissions from plants and microbes. Secondary organic aerosols form when volatile organic compounds undergo oxidation and nucleation, leading to low-volatility products that partition into the particle phase. The chemical composition spans aliphatic hydrocarbons, fatty acids, polycyclic aromatic hydrocarbons, sugars and multifunctional oxidation products. Source apportionment techniques—including molecular markers, stable-isotope signatures and receptor models—have revealed that the relative importance of fossil fuel combustion, biomass burning and biogenic emissions varies by region and season. Organic aerosols influence climate by scattering and absorbing solar radiation and by acting as cloud condensation nuclei, and they affect air quality and human health through respiratory and cardiovascular impacts. An improved mechanistic understanding of their composition, transformation and sources underpins more effective emission control strategies and predictive models of air pollution and climate forcing.

Research from Nature Portfolio

Investigations using compound-specific stable carbon isotopes in urban aerosols have provided nuanced insights into source contributions and atmospheric processing. Analysis of the molecular distributions and δ13C signatures of n-alkanes, fatty acids and alcohols in wintertime Beijing aerosols demonstrated a dominant fossil-fuel signal, as indicated by carbon preference index values near unity. Heavier isotopic compositions on polluted days reflected enhanced photochemical ageing or long-range transport, whereas clearer days bore signatures of more aged biogenic carbon. This approach has proven effective at distinguishing co-emitted sources and quantifying the extent of atmospheric transformation in polluted regions.

Organic Aerosol Composition and Sources publication trend

The graph below shows the total number of articles in organic aerosol composition and sources across all publications each year (not limited to Nature Index journals).

Technical terms

Organic aerosol (OA): Particulate matter composed predominantly of carbon-containing compounds from direct emissions and atmospheric reactions.

Primary organic aerosol (POA): Organic particles emitted directly into the atmosphere from sources such as combustion and biological processes.

Secondary organic aerosol (SOA): Particulate organic material formed by atmospheric oxidation of volatile organic compounds and subsequent gas–particle partitioning.

Carbon Preference Index (CPI): Ratio of odd- to even-carbon chain n-alkanes used to infer biogenic versus fossil-fuel sources.

Tracer compounds: Specific organic molecules that serve as markers for particular emission or formation pathways.

Stable carbon isotopic composition (δ13C): The ratio of 13C to 12C in organic molecules, used to distinguish sources and track chemical processing.

References

1. Molecular distributions and compound-specific stable carbon isotopic compositions of lipids in wintertime aerosols from Beijing. Scientific Reports (2016).
2. Molecular characteristics and diurnal variations of organic aerosols at a rural site in the North China Plain with implications for the influence of regional biomass burning. Atmospheric Chemistry and Physics (2019).
3. Source apportionment of fine particulate matter in Houston, Texas: insights to secondary organic aerosols. Atmospheric Chemistry and Physics (2018).