Photo-oxidation of Nitrophenols in the Aqueous Phase: Reaction Kinetics, Mechanistic Insights, and Evolution of Light Absorption
Abstract
Nitrophenols are a class of water soluble, light absorbing compounds which can make up a significant fraction of biomass burning brown carbon. The atmospheric lifetime and aging of these compounds can have important implications for their impact on climate through the aerosol direct effect. Recent studies have shown that brown carbon aerosols can be bleached of their colour by direct photolysis and photo-oxidation reactions on the timescale of hours to days. However, during aqueous phase photo-oxidation of nitrophenol compounds light absorption is sustained or enhanced, even after the parent nitrophenol molecule has been depleted. In this work, we use online aerosol chemical ionization mass spectrometry (aerosol-CIMS) to investigate the aqueous phase photo-oxidation mechanism and determine the second order rate constants for the reaction of OH radicals with three commonly detected nitrophenol compounds: nitrocatechol, nitroguaiacol, and dinitrophenol. These nitrophenol compounds are found to have aqueous phase lifetimes with respect to oxidation by the OH radical ranging between 5 - 11 hours. Our results indicate that functionalization of the parent nitrophenol molecule by addition of hydroxyl groups leads to the observed absorption enhancement. Further photo-oxidation forms breakdown products that no longer absorb significantly in the visible light range.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A43G2547H
- Keywords:
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- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES