Effect of humidity on the composition of isoprene photooxidation secondary organic aerosol
Open Access
- 18 July 2011
- journal article
- research article
- Published by Copernicus GmbH in Atmospheric Chemistry and Physics
- Vol. 11 (14), 6931-6944
- https://doi.org/10.5194/acp-11-6931-2011
Abstract
The effect of relative humidity (RH) on the composition and concentrations of gas-phase products and secondary organic aerosol (SOA) generated from the photooxidation of isoprene under high-NOx conditions was investigated. Experiments were performed with hydrogen peroxide as the OH precursor and in the absence of seed aerosol. The relative yields of most gas-phase products were the same regardless of initial water vapor concentration with exception of hydroxyacetone and glycolaldehyde, which were considerably affected by RH. A significant change was observed in the SOA composition, with many unique condensed-phase products formed under humid (90 % RH) vs. dry (<2 % RH) conditions, without any detectable effect on the rate and extent of the SOA mass growth. There is a 40 % reduction in the number and relative abundance of distinct particle-phase nitrogen-containing organic compounds (NOC) detected by high resolution mass spectrometry. The suppression of condensation reactions, which produce water as a product, is the most important chemical effect of the increased RH. For example, the total signal from oligomeric esters of 2-methylglyceric acid was reduced by about 60 % under humid conditions and the maximum oligomer chain lengths were reduced by 7–11 carbons. Oligomers formed by addition mechanisms, without direct involvement of water, also decreased at elevated RH but to a much smaller extent. The observed reduction in the extent of condensation-type oligomerization at high RH may have substantial impact on the phase characteristics and hygroscopicity of the isoprene aerosol. The reduction in the amount of organic nitrates in the particle phase has implications for understanding the budget of NOC compounds.Keywords
This publication has 75 references indexed in Scilit:
- Gas-phase water-mediated equilibrium between methylglyoxal and its geminal diolProceedings of the National Academy of Sciences, 2010
- Organic speciation of atmospheric particles in Alvão Natural Park (Portugal)Environmental Monitoring and Assessment, 2009
- Oligomers formed through in-cloud methylglyoxal reactions: Chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR mass spectrometryAtmospheric Environment, 2007
- Detection of C1–C5 alkyl nitrates by proton transfer reaction time-of-flight mass spectrometryInternational Journal of Mass Spectrometry, 2007
- Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—2. Dialdehydes, methylglyoxal, and diketonesAtmospheric Environment, 2005
- Measurements of Secondary Organic Aerosol from Oxidation of Cycloalkenes, Terpenes, and m-Xylene Using an Aerodyne Aerosol Mass SpectrometerEnvironmental Science & Technology, 2005
- Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1: aldehydes and ketonesAtmospheric Environment, 2004
- Atmospheric Degradation of Volatile Organic CompoundsChemical Reviews, 2003
- Atmospheric Chemistry of Biogenic Organic CompoundsAccounts of Chemical Research, 1998
- Capillary electrophoresis to analyze water-soluble oligo(hydroxyacids) issued from degraded or biodegraded aliphatic polyestersJournal of Polymers and the Environment, 1996