Abstract
Previous research on atmospheric chemistry in the forest environment has shown that the total reactivity by biogenic volatile organic compound (BVOC) emission is not well considered in for-est chemistry models. One possible explanation for this discrepancy is the unawareness and ne-glect of reactive biogenic emission that have eluded common monitoring methods. This ques-tion motivated the development of a total ozone reactivity monitor (TORM) for the direct de-termination of the reactivity of foliage emissions. Emissions samples drawn from a vegetation branch enclosure experiment are mixed with a known and controlled amount of ozone (e.g. re-sulting in 100 ppb of ozone) and directed through a temperature-controlled glass flow reactor to allow reactive biogenic emissions to react with ozone during the approximately 2-minute residence time in the reactor. The ozone reactivity is determined from the difference in the ozone mole fraction before and after the reaction vessel. An inherent challenge of the experi-ment is the influence of changing water vapor in the sample air on the ozone signal. A com-mercial UV absorption ozone monitor was modified to directly determine the ozone differential with one instrument and sample air was drawn through Nafion dryer membrane tubing. These two modifications significantly reduced errors associated with the determination of the reacted ozone compared to determining the difference from two individual measurements and errors from interferences from water vapor, resulting in a much improved and sensitive determina-tion of the ozone reactivity. This paper provides a detailed description of the measurement de-sign, the instrument apparatus, and its characterization. Examples and results from field de-ployments demonstrate the applicability and usefulness of the TORM.
Highlights
Recent field research on the atmospheric chemistry in forest environments has yielded a series of results that cannot be explained with our current comprehension of biogenic emissions, Di Carlo et al [2004] that stimulated new interest and research into the question of unaccounted rectly measured hydroxyl radical (OH) reactivity in ambient air at the University of Michigan Biodeposition processes, and chemical reactions
0.1 – 0.2 ppb, which was 2-3 times lower than the calculated ozone difference from the twomonitor measurement. These results clearly indicate the benefits of the single monitor measuretwo-monitor determination; (2) there is a very significant improvement in the measurement prelabor intensive as it does not require the regular intercomparison for determination of offsets ment: (1) the accuracy of the ozone reactivity measurement is consistent with the differential cision from using a single monitor; and (3) the operation of a single monitor is less tedious and c Author(s) 2021
total ozone reactivity monitor (TORM) builds on standard laboratory equipment and can be assembled thoroughly characterized, and a number of ameliorations were implemented that significantly water vapor in the sample air
Summary
Recent field research on the atmospheric chemistry in forest environments has yielded a series of results that cannot be explained with our current comprehension of biogenic emissions, Di Carlo et al [2004] that stimulated new interest and research into the question of unaccounted rectly measured hydroxyl radical (OH) reactivity in ambient air at the University of Michigan Biodeposition processes, and chemical reactions. These findings date back to the pivotal paper by for biogenic volatile organic compound (BVOC) emissions. This similarity led the authors to hypothesize that the missing OH reactivity is
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