What are secondary organic aerosols (SOA) and how are they formed?

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What are secondary organic aerosols (SOA) and how are they formed?

SOA are particles that form in the atmosphere when volatile organic compounds are oxidized, typically by OH radicals, into products with much lower volatility. These low-volatility products can then partition into existing particles or nucleate new ones, gradually growing into measurable aerosols. This is a secondary formation process—the aerosol is created from other compounds after emission rather than being emitted directly. VOCs come from both natural sources like trees and human activities such as vehicle exhaust and solvent use. The oxidation chain (with OH, and sometimes ozone or nitrate radicals) produces products that tend to stick to particle surfaces or rise up as new particles, especially under conditions that favor condensation. Temperature, the amount of existing organic matter, and oxidant levels influence how much SOA forms. Directly emitted soot is a primary aerosol, not SOA. Inorganic salts from sea spray are inorganic aerosols, not organic. And gaseous pollutants aren’t aerosols themselves, though they can become part of SOA after oxidation and condensation.

SOA are particles that form in the atmosphere when volatile organic compounds are oxidized, typically by OH radicals, into products with much lower volatility. These low-volatility products can then partition into existing particles or nucleate new ones, gradually growing into measurable aerosols. This is a secondary formation process—the aerosol is created from other compounds after emission rather than being emitted directly.

VOCs come from both natural sources like trees and human activities such as vehicle exhaust and solvent use. The oxidation chain (with OH, and sometimes ozone or nitrate radicals) produces products that tend to stick to particle surfaces or rise up as new particles, especially under conditions that favor condensation. Temperature, the amount of existing organic matter, and oxidant levels influence how much SOA forms.

Directly emitted soot is a primary aerosol, not SOA. Inorganic salts from sea spray are inorganic aerosols, not organic. And gaseous pollutants aren’t aerosols themselves, though they can become part of SOA after oxidation and condensation.

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