Photolytic processing of secondary organic aerosols dissolved in cloud droplets

Journal Article · Thu May 26 04:00:00 EDT 2011 · Physical Chemistry Chemical Physics. PCCP (Print)

DOI:https://doi.org/10.1039/c1cp20526a· OSTI ID:1019181

Bateman, Adam P; Nizkorodov, Serguei; Laskin, Julia; Laskin, Alexander

The effect of UV irradiation on the molecular composition of aqueous extracts of secondary organic aerosol (SOA) was investigated. SOA was prepared by the dark reaction of ozone and d-limonene at 0.05 - 1 ppm precursor concentrations and collected with a particle-into-liquid sampler (PILS). The PILS extracts were photolyzed by 300 - 400 nm radiation for up to 24 hours. Water-soluble SOA constituents were analyzed using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) at different stages of photolysis for all SOA precursor concentrations. Exposure to UV radiation increased the average O/C ratio and decreased the average double bond equivalent (DBE) of the dissolved SOA compounds. Oligomeric compounds were significantly reduced by photolysis relative to the monomeric compounds. Direct pH measurements showed that compounds containing carboxylic acids increased upon photolysis. Methanol reactivity analysis revealed significant photodissociation of molecules containing carbonyl groups and formation of carboxylic acids. Aldehydes, such as limononaldehyde, were almost completely removed. The removal of carbonylswas confirmed by the UV-Vis absorption spectroscopy of the SOA extracts where the absorbance in the carbonyl n→π* band decreased significantly upon photolysis. The effective quantum yield (the number of carbonyls destroyed per photon absorbed) was estimated as ~ 0.03. The concentration of peroxides did not change significantly during photolysis as quantified with an iodometric test. Although organic peroxides were photolyzed, the likely end products of photolysis were smaller peroxides, including hydrogen peroxide, resulting in a no net change in the peroxide content.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1019181
• Report Number(s): PNNL-SA-78898; 39957; KP1704020
• Journal Information: Physical Chemistry Chemical Physics. PCCP (Print), Journal Name: Physical Chemistry Chemical Physics. PCCP (Print) Journal Issue: 26 Vol. 13; ISSN 1463-9076
• Publisher: Royal Society of Chemistry
• Country of Publication: United States
• Language: English

Related Subjects

10 SYNTHETIC FUELS
ABSORPTION SPECTROSCOPY
AEROSOLS
ALDEHYDES
CARBONYLS
CARBOXYLIC ACIDS
CLOUDS
DOUBLE BONDS
DROPLETS
Environmental Molecular Sciences Laboratory
HYDROGEN PEROXIDE
IONIZATION
IRRADIATION
MASS SPECTROSCOPY
METHANOL
OZONE
PEROXIDES
PHOTOLYSIS
PHOTONS
PRECURSOR
RADIATIONS
REMOVAL
SAMPLERS