Total OH reactivity measurements in ambient air in a southern Rocky mountain ponderosa pine forest during BEACHON-SRM08 summer campaign

Yoshihiro Nakashima,Shungo Kato,Jim Greenberg,Peter Harley,Thomas Karl,Andrew Turnipseed,Eric Apel,Alex Guenther,Jim Smith,Yoshizumi Kajii

doi:10.1016/j.atmosenv.2013.11.042

Abstract

Total OH reactivity was measured during the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen-Southern Rocky Mountain 2008 field campaign (BEACHON-SRM08) held at Manitou Experimental Forest (MEF) in Colorado USA in August, 2008. The averaged total OH reactivity was 6.7 s−1, smaller than that measured in urban (33.4 s−1, Yoshino et al., 2012) and suburban (27.7 s−1, Yoshino et al., 2006) areas in Tokyo in the same season, while sporadically high OH reactivity was also observed during some evenings. The total OH reactivity measurements were accompanied by observations of traces species such as CO, NO, NOy, O3 and SO2 and Volatile Organic Compounds (VOCs). From the calculation of OH reactivity based on the analysis of these trace species, 46.3% of OH reactivity for VOCs came from biogenic species that are dominated by 2-methyl-3-buten-2-ol (MBO), and monoterpenes. MBO was the most prominent contribution to OH reactivity of all trace species. A comparison of observed and calculated OH reactivity shows that the calculated OH reactivity is 29.5% less than the observed value, implying the existence of missing OH sinks. One of the candidates of missing OH is thought to be the oxidation products of biogenic species.

Highlights

Volatile organic compounds (VOCs) play an important role in the formation of photochemical oxidants and secondary organic aerosol resulting from reactions with OH, O3, NO3, etc. (FinlaysonPitts and Pitts, 2000)
Diurnal variation of O3 and the high concentration indicates that ozone formation process undergoes in Manitou Experimental Forest (MEF) by the reaction of ambient OH and VOCs
Total OH reactivity was measured in a southern Rocky mountain forest consisting mainly of ponderosa pine trees in summer 2008

Summary

Introduction

Volatile organic compounds (VOCs) play an important role in the formation of photochemical oxidants and secondary organic aerosol resulting from reactions with OH, O3, NO3, etc. (FinlaysonPitts and Pitts, 2000). Peeters et al (2009) have proposed a different chemical process for the formation of OH during isoprene oxidation under low NOx condition. They have suggested that isomerization of a peroxy radical generated by the reaction of isoprene with OH under low NOx is caused, so called the 1, 5 and 1, 6-H shifts, resulting of the production of HO2 and unsaturated hydroxyperoxide-aldehydes (HPALDs) and OH forms through the photolysis of HPALDs. To estimate the formation of photochemical oxidants and the amount of HOx, it is essential to clarify the loss and production processes of HOx, identify the oxidation products of the photochemical reaction of BVOCs, and determine their chemical properties

Methods

Results

Conclusion