Total OH reactivity measurements at Manitou Experimental Forest in summer season during BEACHON-SRM08
Abstract
The hydroxyl radical (OH) is well known to play a central role in initiating the oxidation of a number of atmospheric species. Measurement of total OH reactivity is important not only to understand mechanisms of oxidant formation in the troposphere but also to estimate the total amount of trace gas species, especially volatile organic compounds (VOCs). We have developed an OH reactivity measurement system using a laser pump probe technique. OH was artificially generated by the photolysis of ozone to produce O(1D) followed by reaction of O(1D) with water vapor. The lifetime of OH was then measured by a laser induced fluorescence technique. We measured OH reactivity at urban and suburban areas of Tokyo and confirmed the existence of unknown reactive species. The measurement of OH reactivity in rural areas where the effect of anthropogenic emissions is thought to be small is another essential test to ascertain the existence of unknown species and their oxidant formation potential. Total OH reactivity was measured at Manitou Experimental Forest (MEF) during August 8th-6thand 22th-28th, 2008. MEF is located in the southern part of the Rocky Mountains and about 80 km south from Denver. MEF is covered with ponderosa pine and observations indicate that the effect of anthropogenic emissions is small. The value of OH reactivity was about 5-10 s-1, smaller than that measured in urban or suburban areas of Tokyo. During the measurement period, a strong thunderstorm and tornado formed near MEF: this coincided with a rapid increase in OH reactivity. Sporadically high OH reactivity was also observed during some days due to transport of pollutants from the Front Range Urban Corridor. Together with the measurement of OH reactivity, traces species such as CO, NO, NOy, O3 and SO2 were analyzed. VOCs were analyzed by GC-FID and PTR-MS techniques. From the calculation of OH reactivity based on the analysis of traces species, about 60% of OH reactivity for VOCs came from biogenic VOCs that are dominated by a hemiterpene, 2-methyl-3-butene-2-ol(MBO), and five monoterpene species. A comparison of observed and calculated OH reactivity shows that the calculated OH reactivity is about 50% less than the observed value. These measurements were carried out at the part of the BEACHON-SRM08 project.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A21C0182N
- Keywords:
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- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0399 ATMOSPHERIC COMPOSITION AND STRUCTURE / General or miscellaneous