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 HO2EPA 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.