Peroxy radical concentrations measured and calculated from trace gas measurements in the Mauna Loa Observatory Photochemistry Experiment 2

Abstract

Measurements of peroxy radical concentrations ([HO2] + [RO2] ) were made by the "chemical amplifier" technique during the four intensives of the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) at the Mauna Loa Observatory in 1991-1992. In this study these data are compared with the theoretical values of the peroxy radical concentrations obtained from steady state analysis of the complete suite of trace gas measurements and other relevant parameters also measured during the experiment. The data from 33 days of the study contain time overlap of the concentration and physical data which allow a meaningful theoretical treatment. The experimental results for [HO2] + [RO2] agree well with theory for many of the days, but are significantly suppressed from the theoretical expectations on other days. Two hypotheses are presented and tested to explain the observed suppression. The first involves the reaction of the peroxy radicals at aerosol surfaces. The second proposes the loss of [OH] through its reaction with unknown and undetected species to develop peroxy radicals subsequently to which the "chemical amplifier" is insensitive. Evidence at hand does not allow a clear choice between these or possible alternative explanations. The data suggest that the net rate of 0 3 generation in the 1 free troposphere is about-1.5 parts per billion by volume per day (ppbv d-; 24-hour average). CH30 2. At sites in highly forested areas and in polluted regions, a large variety of organic peroxy radicals is expected since many reactive hydrocarbons in addition to CH 4 react with the OH radical to form different RO 2 species. One of the important aspects of the peroxy radicals in atmospheric chemistry is their ability to oxidize NO to NO 2 with subsequent ozone generation: HO 2 + NO --> HO + NO 2 RO 2 + NO --> RO + NO 2 NO 2 + h v --> O(3p) + NO O(3p) + 02 (+M) --> 03 (+M) Paper number 95JD03613. 0148-0227/96/95 JD-03613509.00 HO 2 + 03 --> HO + 202 HO + 03 --> HO 2 + 02 The relative importance of the 03 formation, stratospherictropospheric transport, and chemical and physical removal pathways determines whether 03 builds or is depleted in the troposphere. , The HO 2 and RO 2 radicals are also important as major sources of peroxides in the atmosphere (H202, CH302H, etc.). Studies made during the Mauna Loa Observatory Photochemistry Experiment 1 (MLOPEX 1) have been used to estimate the rate of ozone production in the free troposphere as about-0.5 parts per billion by volume per day (ppbv d-i; 24hour average) for upslope air and -0.9 ppbv d -1 for free tropospheric air [Ridley et al., 1992]. Although most of the important trace gases were measured during these studies, several key elements for the calculation had to be estimated from theory or inferred from indirect estimates. Thus the most important loss rate for ozone is ozone photodissociation into O(1D); this was not measured but was estimated from theory. In addition, the concentrations of HO 2, CH302 , and OH could not be measured but were estimated from photostationary ...

Some considerations of the origin of nighttime peroxy radicals observed in MLOPEX 2

“…Measured simultaneously in this remote atmosphere were the important transient [OH], most of the trace gases, and pertinent meteorological information. The results of the daytime radical concentrations during MLOPEX and other studies were discussed in previous publications [Cantrell et al, 1996a[Cantrell et al, ,b,c, 1997aEisele et al, 1996]. In this study we focus on the measured nighttime radicals during MLOPEX 2.…”

“…The observations shown in Figure 1 are roughly in accord with this idea. During the daylight hours at Mauna Loa Observatory HO 2 and CH30 2 radicals are the major peroxy radicals [Cantrell et 'al., 1996a]. In theory the reactions of NO 3 radical with various organic trace gases in the troposphere can develop RO2 radicals.…”

Technical Note: Characterisation of a DUALER instrument for the airborne measurement of peroxy radicals during AMMA 2006

“…Since this technique was proposed by Cantrell and Stedman (1982) and calibrated by Hastie et al (1991), there is abundant literature describing its gradual improvement and characterisation for the ambient measurement of peroxy radicals, and its deployment in diverse polluted and remote areas (e.g. Monks et al, 1996;Carslaw et al, 1999;Burkert et al, 2001aBurkert et al, , b, 2003Andrés-Hernández et al, 2001;Cantrell et al, 1996a;Volz-Thomas et al, 2003;Zanis et al, 2003;Fleming et al, 2006a, b).…”

Peroxy radical observations using chemical ionization mass spectrometry during TOPSE

“…[15] For this study, concentrations were calculated using the assumption of steady state, and constraining the governing equations by the observed trace gas concentrations and photolysis rate coefficients [Cantrell et al, , 1996b. The estimated accuracy of these calculations is ±40% (95% confidence interval), with uncertainties due to rate coefficients and trace gas concentrations.…”

“…Filled circles are from this study. Open squares include data involving groups from NCAR including the Tropospheric OH Photochemistry Experiment [Cantrell et al, 1997b], MLOPEX 1 [Ridley et al, 1992], MLOPEX 2 [Cantrell et al, 1996a[Cantrell et al, , 1996b, ROSE 1 [Cantrell et al, 1992, and FIELDVOC 1 [Cantrell et al, 1996c]. Triangles signify data collected during NASA-GTE missions including PEM-Tropics A (model results) [Olsen et al, 2001] and PEM-Tropics B [Tan et al, 2001].…”