Measurements of tropospheric HO2 and RO2 by oxygen dilution modulation and chemical ionization mass spectrometry
Item
Title (Dublin Core)
Measurements of tropospheric HO2 and RO2 by oxygen dilution modulation and chemical ionization mass spectrometry
Description (Dublin Core)
An improved method for the measurement of hydroperoxy radicals (HO<sub>2</sub>) and organic peroxy radicals (RO<sub>2</sub>, where R is any organic group) has been developed that combines two previous chemical conversion/chemical ionization mass spectrometry (CIMS) peroxy radical measurement techniques. Applicable to both ground-based and aircraft platforms, the method provides good separation between HO<sub>2</sub> and RO<sub>2</sub> and frequent measurement capability with observations of both HO<sub>2</sub> and HO<sub>2</sub> + RO<sub>2</sub> amounts each minute. This allows for analyses of measured [HO<sub>2</sub>]/[HO<sub>2</sub> + RO<sub>2</sub>] ratios on timescales relevant to tropospheric photochemistry. By varying both [NO] and [O<sub>2</sub>] simultaneously in the chemical conversion region of the PeRCIMS (Peroxy Radical CIMS) inlet, the method exploits the changing conversion efficiency of RO<sub>2</sub> to HO<sub>2</sub> under different inlet [NO]/[O<sub>2</sub>] to selectively observe either primarily HO<sub>2</sub> or the sum of HO<sub>2</sub> and RO<sub>2</sub>. Two modes of operation have been established for ambient measurements: in the first half of the minute, RO<sub>2</sub> radicals are measured at close to 100% efficiency along with HO<sub>2</sub> radicals (low [NO]/[O<sub>2</sub>] = 2.53 × 10<sup>−5</sup>) and in the second half of the minute, HO<sub>2</sub> is detected while the majority of ambient RO<sub>2</sub> radicals are measured with approximately 15% efficiency (high [NO]/[O<sub>2</sub>] = 6.80 × 10<sup>−4</sup>). The method has been tested extensively in the laboratory under various conditions and for a variety of organic peroxy radicals relevant to the atmosphere and the results of these tests are presented. The modified PeRCIMS instrument has been deployed successfully using the current measurement technique on a number of aircraft campaigns, including on the NSF/NCAR C-130 during the MIRAGE-Mex and NASA INTEX-B field campaigns in the spring of 2006. A brief comparison of the peroxy radical measurements during these campaigns to a photochemical box model confirms that the PeRCIMS is able to successfully separate and measure HO<sub>2</sub> and RO<sub>2</sub> under the majority of tropospheric conditions.
Creator (Dublin Core)
Hornbrook, R. S.
Crawford, J. H.
Edwards, G. D.
Goyea, O.
Mauldin III, R. L.
Olson, J. S.
Cantrell, C. A.
Date (Dublin Core)
2018-08-11
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acpd-10-22219-2010
https://acp.copernicus.org/preprints/acp-2010-672/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
