Abstract
A new system that uses the total reactivity with ozone (RO3) was developed for measuring biogenic volatile organic compounds (BVOCs) emitted from vegetation into the atmosphere. The decrease in ozone caused by the reaction with VOCs was monitored at the ppbv level by dual chemiluminescence detectors (CLDs) based on the NO-O3 reaction. Ozone was monitored by the dual CLDs before and after the reactor to correct for fluctuations in the ozone concentration. Such dual detectors can remove the interference caused by water vapor. A glass double-tube was adopted as the reactor. The loss rate of ozone to the wall was typically (6 ± 3) × 10–4 s–1. Gaseous cyclohexane was also added to the sample before it was introduced into the reactor to scavenge secondary OH radicals. From the characterization of the RO3 analyzer using the standard VOC sample, the dependence of ozone reduction on the reaction time and reactivity were shown to agree with theoretical predictions. A calibration procedure for determining the reaction time was also established. Consequently, the detection limit for RO3 in a 57-s reaction was determined to be 1.4 × 10–4 s–1 (S/N = 3), which corresponded to 27 ppbv of limonene. It was confirmed that the RO3 analyzer was capable of measuring BVOC levels. Finally, a practical trial was conducted in which BVOCs emitted from a real needle-leaf tree were monitored. BVOC emissions from the tree were detected and a significant increase in RO3 was observed when the tree was irradiated with light.
Highlights
Volatile organic compounds (VOCs) have been focused on in atmospheric chemistry as critical precursors of photochemical oxidants and secondary organic aerosols (SOAs) (Atkinson, 2000; Donahue et al, 2009)
A new system that uses the total reactivity with ozone (RO3) was developed for measuring biogenic volatile organic compounds (BVOCs) emitted from vegetation into the atmosphere
This study focuses on the high reactivity of BVOCs with ozone, and a new tool employing this ozone reactivity (RO3) for BVOC measurements is proposed
Summary
Volatile organic compounds (VOCs) have been focused on in atmospheric chemistry as critical precursors of photochemical oxidants and secondary organic aerosols (SOAs) (Atkinson, 2000; Donahue et al, 2009). When VOCs are emitted into the atmosphere, they react with atmospheric radicals such as the hydroxyl radical (OH), ozone (O3), and the nitrate radical (NO3). The initial reactions of VOCs with atmospheric radicals are important for both the atmospheric degradation of VOCs and production of oxidants and SOAs. VOCs can react with radical X to form peroxy radicals such as HO2 and RO2, where R represents an organic functional group. Semi-volatile organic compounds, SVOCs, are formed as secondary products of reactions of VOCs with atmospheric radicals. Condensation of SVOCs with low vapor pressures is critical for the formation of SOAs because of the following reaction
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