A Role for 2-Methyl Pyrrole in the Browning of 4-Oxopentanal and Limonene Secondary Organic Aerosol
[2];
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[1]
- Department of Chemistry, University of California, Irvine, California 92697, United States
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
- Environmental Molecular Science Laboratory, Energy and Environment Directorate, , Pacific Northwest National Laboratory, Richland, Washington 99354, United States
“Brown Carbon” (BrC) is a type of organic particulate matter that absorbs visible and near ultraviolet radiation. Reactions of carbonyls in secondary organic aerosol (SOA) produced from limonene with ammonia (NH3) or ammonium sulfate (AS) are known to produce BrC with a distinctive absorption band at 500 nm. Although the general mechanism for this process has been proposed in previous studies, the specific molecular structures of the light-absorbing species remain unclear. This study examined the browning processes occurring in aqueous solutions of AS and 4-oxopentanal (4-OPA), which has a 1,4-dicarbonyl structural motif present in many limonene SOA compounds. The reaction of 4-OPA with AS in a bulk aqueous solution produces a 2-methyl pyrrole (2-MP) intermediate, which is not a strong light absorber by itself, but can react further with carbonyl compounds leading to the eventual formation of BrC chromophores. The direct involvement of 2-MP in the browning process was demonstrated by reacting 2-MP with 4-OPA and with limonene SOA, both of which produced BrC chromophores with distinctive absorption bands at visible wavelengths. The formation of BrC in reaction of 4-OPA with AS and ammonium nitrate (AN) was found to be accelerated by evaporation of the solution suggesting an important role of the dehydration processes in BrC formation from 1,4- dicarbonyls. 4-OPA was also found to produce BrC in aqueous reactions with a broad spectrum of amino acids and amines. The results suggest that 4-OPA may be the smallest atmospherically relevant compound capable of browning by the same mechanism as limonene SOA.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1406664
- Report Number(s):
- PNNL-SA-126022; 49352; KP1704020
- Journal Information:
- Environmental Science and Technology, Vol. 51, Issue 19; ISSN 0013-936X
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
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