RO2 and HOx Radicals in Urban and Rural Air: Measurements of OH and RO2 Formation From Ozone-Alkene Reactions, and the Rate Coefficients of the Reactions of High Molecular Weight RO2 Radicals with HO2

EPA Grant Number: R826236
Title: RO2 and HOx Radicals in Urban and Rural Air: Measurements of OH and RO2 Formation From Ozone-Alkene Reactions, and the Rate Coefficients of the Reactions of High Molecular Weight RO2 Radicals with HO2
Investigators: Paulson, Suzanne , Sander, Stanley
Institution: University of California - Los Angeles
EPA Project Officer: Shapiro, Paul
Project Period: January 15, 1998 through January 14, 2001
Project Amount: $440,323
RFA: Ambient Air Quality (1997) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Description:

HOx (= HO, RO2 and HO2) radicals initiate and propagate the chain reactions that lead to ozone formation in the troposphere. Understanding their sources and loss processes is key to understanding photochemical ozone and smog formation in urban and rural areas. Recent results indicate that ozone-alkene reactions can be the dominant source of new HOx radicals in urban air, producing more HOx at noon than ozone photolysis. Ozone-alkene reactions are also a significant source of HOx in rural air. Several OH radical yields have been measured, and range from 0.1 to 1 per ozone-alkene reaction, with an uncertainty of a factor of ?1.5 or more. Objective 1) is to quantify OH radical yields with high precision (?15-25%). The most likely mechanism for OH formation predicts an equal amount of RO2 concomitant with OH formation. This mechanism doubles the radical yields from ozone-alkene reactions, but has yet to be experimentally proven. Objective 2) is to probe RO2 formation from ozone-alkene reactions.

The oxidant and ozone levels in most rural air are strongly influenced by reactions of HO2 with RO2 radicals produced from the reactions of biogenic alkenes and may contribute to particulate formation. The existing data base of rate constants for reactions of larger RO2 radicals with HO2 is highly inadequate for the purposes of atmospheric modeling in both the accuracy and the number of reactions studied. Objective 3) is to accurately measure the rate coefficients reactions of representative large RO2 radicals with HO2.

Approach:

1) A new small-ratio relative rate method is proposed to measure OH radical yields with high precision (?10-15%). 2) A fast-turbulent flow reactor using Fourier Transform Infrared spectroscopy and High Pressure Liquid Chromatography is proposed to probe RO2 formation from ozone-alkene reactions, to test the proposed OH formation mechanism. 3) A new technique called Infrared Kinetic Spectroscopy is proposed for the study of RO2 reactions with HO2.

Expected Results:

The result expected from objectives 1) and 2) is an improved ability to model urban ozone formation and devise effective control strategies. Currently, chain initiators (new HOx radicals) in smog formation are probably underestimated by 20-60%, and this may account for a significant portion of the under-prediction of ozone formation by urban airshed models. The results expected from objectives 1)-3) are expected to significantly improve the ability to model ozone and particulate formation in rural areas.

Publications and Presentations:

Publications have been submitted on this project: View all 30 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 10 journal articles for this project

Supplemental Keywords:

Tropospheric ozone, urban ozone, ambient air, VOC's, oxidants, organics, toxics, particulates, exposure., RFA, Scientific Discipline, Air, particulate matter, air toxics, Environmental Chemistry, tropospheric ozone, Atmospheric Sciences, Environmental Engineering, ambient air quality, particle size, particulates, urban air toxics, ozone-alkene reactions, air pollutants, chemical characteristics, ozone occurrence, photochemical radical, ambient air, ambient measurement methods, ozone, ambient monitoring, chemical composition, photochemical smog, smog, urban air pollutants, atmosphere, infrared spectroscopy, chain reactions, Alkene reactions, photochemical assessment, Volatile Organic Compounds (VOCs)

Relevant Websites:

http://pubs.acs.org/cgi-bin/doilookup/?10.1021/jp993611q

Progress and Final Reports:

  • 1998 Progress Report
  • 1999 Progress Report
  • Final Report