Sources and Cycling of Tropospheric Hydroxyl Radicals – An Overview
-
Yasin Elshorbany
Abstract
The hydroxyl radical is the principal oxidizing agent in the troposphere. It controls and determines the oxidizing power of the atmosphere and thus governs the atmospheric lifetime of many species, and their potential to contribute to climate change, air pollution and ozone formation. Owing to the development of new measurement techniques and the discovery of new reaction mechanisms, the understanding of the OH chemistry has witnessed significant advances during the last decades. This article presents a comprehensive review of the current understanding of OH radical chemistry with an outlook to future work in this active research area of atmospheric chemistry.Among the different OH radical initiation sources, e.g. O3 photolysis, HCHO photolysis, ozonolysis of alkenes and the photolysis of nitrous acid (HONO), the latter has been shown in recent field and model studies to make a major contribution to tropospheric OH levels. New photochemical sources of HONO have been discovered in the laboratory which can explain unexpectedly high concentrations of HONO observed in the atmosphere during daytime. A detailed analysis of HONO sources in the atmosphere is presented. OH radicals react with volatile organic compounds (VOCs) in a complex cycle regenerating OH radicals in the propagation cycle. Recent field and model studies show that the OH radical propagation cycle is balanced for high NOx conditions. Thus, radical losses by reactions with VOCs are balanced by OH formation through the reaction HO2+NO. However, studies at low NO and high VOC levels imply that unknown radical sources of OH exist in rural and forested areas. Possible sources of OH radicals under these conditions are discussed.
© by Oldenbourg Wissenschaftsverlag, Wuppertal, Germany
Articles in the same Issue
- Physico-Chemical Aspects of Global Atmospheric Change. Dedicated to Reinhard Zellner on the occasion of his 65th birthday
- The Quest for the Hydroxyl-Peroxy Radical
- Sources and Cycling of Tropospheric Hydroxyl Radicals – An Overview
- Kinetics and Products of the Reaction O2(1Σg+) with N2O
- An Experimental and Theoretical Study of the Reaction Between NH(X3Σ−) + SO(X3Σ−)
- Pressure Dependence of Iso-Propyl Nitrate Formation in the i-C3H7O2 + NO Reaction
- Photolysis of Trichloronitromethane (Chloropicrin) under Atmospheric Conditions
- The Gas-phase Ozonolysis of 1-Penten-3-ol, (Z)-2-Penten-1-ol and 1-Penten-3-one: Kinetics, Products and Secondary Organic Aerosol Formation
- Theoretical Study of the HOCH2OO• + HO2• Reaction: Detailed Molecular Mechanisms of the Three Reaction Channels
- Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor
- Heterogeneous Chemistry of Cl2O and HOCl on Frozen Natural Sea Salt, Recrystallized Sea Salt, KCl and NaCl Solutions at 200 and 215 K
- Atmospheric Heterogeneous Reactions of Benzo(a)pyrene
- Time Resolved Infrared Spectroscopy of Formation and Processing of Secondary Organic Aerosol
- Probing the Equilibrium Size and Hydrogen Bonding Structure in Aqueous Aerosol Droplets
- Interaction of NO2 with Soot: Oxidation and Gasification at Temperatures Between 300 and 670 K
- Uptake of Organic Acids on Ice Surfaces: Evidence for Surface Modification and Hydrate Formation
- Aqueous Phase Reactivity of Nitrate Radicals (NO3) Toward Dicarboxylic Acids
- Temperature and Ionic Strength Dependence of NO3-radical Reactions with Substituted Phenols in Aqueous Solution
Articles in the same Issue
- Physico-Chemical Aspects of Global Atmospheric Change. Dedicated to Reinhard Zellner on the occasion of his 65th birthday
- The Quest for the Hydroxyl-Peroxy Radical
- Sources and Cycling of Tropospheric Hydroxyl Radicals – An Overview
- Kinetics and Products of the Reaction O2(1Σg+) with N2O
- An Experimental and Theoretical Study of the Reaction Between NH(X3Σ−) + SO(X3Σ−)
- Pressure Dependence of Iso-Propyl Nitrate Formation in the i-C3H7O2 + NO Reaction
- Photolysis of Trichloronitromethane (Chloropicrin) under Atmospheric Conditions
- The Gas-phase Ozonolysis of 1-Penten-3-ol, (Z)-2-Penten-1-ol and 1-Penten-3-one: Kinetics, Products and Secondary Organic Aerosol Formation
- Theoretical Study of the HOCH2OO• + HO2• Reaction: Detailed Molecular Mechanisms of the Three Reaction Channels
- Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor
- Heterogeneous Chemistry of Cl2O and HOCl on Frozen Natural Sea Salt, Recrystallized Sea Salt, KCl and NaCl Solutions at 200 and 215 K
- Atmospheric Heterogeneous Reactions of Benzo(a)pyrene
- Time Resolved Infrared Spectroscopy of Formation and Processing of Secondary Organic Aerosol
- Probing the Equilibrium Size and Hydrogen Bonding Structure in Aqueous Aerosol Droplets
- Interaction of NO2 with Soot: Oxidation and Gasification at Temperatures Between 300 and 670 K
- Uptake of Organic Acids on Ice Surfaces: Evidence for Surface Modification and Hydrate Formation
- Aqueous Phase Reactivity of Nitrate Radicals (NO3) Toward Dicarboxylic Acids
- Temperature and Ionic Strength Dependence of NO3-radical Reactions with Substituted Phenols in Aqueous Solution
