Primary and Secondary Sources of Gas-Phase Organic Acids from Diesel Exhaust

Beth Friedman, Michael F. Link, S. Ryan Fulgham, Patrick Brophy, Abril Galang, William H. Brune, Shantanu H. Jathar, Delphine K. Farmer

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Organic acids have primary and secondary sources in the atmosphere, impact ecosystem health, and are useful metrics for identifying gaps in organic oxidation chemistry through model-measurement comparisons. We photooxidized (OH oxidation) primary emissions from diesel and biodiesel fuel types under two engine loads in an oxidative flow reactor. formic, butyric, and propanoic acids, but not methacrylic acid, have primary and secondary sources. Emission factors for these gas-phase acids varied from 0.3-8.4 mg kg-1 fuel. Secondary chemistry enhanced these emissions by 1.1 (load) to 4.4 (idle) × after two OH-equivalent days. The relative enhancement in secondary organic acids in idle versus loaded conditions was due to increased precursor emissions, not faster reaction rates. Increased hydrocarbon emissions in idle conditions due to less complete combustion (associated with less oxidized gas-phase molecules) correlated to higher primary organic acid emissions. The lack of correlation between organic aerosol and organic acid concentrations downstream of the flow reactor indicates that the secondary products formed on different oxidation time scales and that despite being photochemical products, organic acids are poor tracers for secondary organic aerosol formation from diesel exhaust. Ignoring secondary chemistry from diesel exhaust would lead to underestimates of both organic aerosol and gas-phase organic acids.

Original languageEnglish (US)
Pages (from-to)10872-10880
Number of pages9
JournalEnvironmental Science and Technology
Issue number18
StatePublished - Sep 19 2017

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Environmental Chemistry


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