Abstract
The gas phase hydrogen peroxide and methylhydroperoxide concentrations were measured in the troposphere over the tropical Pacific Ocean as a component of NASA's Global Tropospheric Experiment/Pacific Exploratory Mission‐Tropics A field campaign. Flights on two aircraft covered the Pacific from 70°S to 60°N and 110°E to 80°W and South Atlantic from 40°S to 15°N and 45°W to 70°E, and extending from 76 to 13,000 m altitude. H2O2 and CH3OOH have the highest concentrations at a given altitude at the equator and decrease with increasing latitude in both the northern and southern hemispheres. Above 4 km the gradient is substantially reduced for both H2O2 and CH3OOH with latitude, and at altitudes in excess of 8 km there is no latitudinal dependence. H2O2 and CH3OOH exhibit maximum mixing ratios between 1 and 2 km at all latitudes. The mean mixing ratio of H2O2 at the equator was 1600±600 parts per trillion by volume (pptv) decreasing to 500±250 pptv at latitudes greater than 55° north and south between 1 and 2 km altitude. CH3OOH at the equator was 1400±250 pptv, decreasing to 330±200 pptv at high latitudes at altitudes between 1 and 2 km. The concentration of peroxides at high latitudes in the northern hemisphere was generally a factor of 2 higher than at corresponding latitudes in the southern hemisphere. The ratio of H2O2 to CH3OOH was between 1 and 2 from 45°S to 35°N at altitudes below 4 km. Between 5° to 15°N the ratio is less than 1, due to preferential removal of H2O2 in the Intertropical Convergence Zone.
Highlights
In this paper we present the distribution of H202 and presenceof peroxyfunctionalgroupsat elevatedp H
H202 and CH3OOH were the principalhydroperoxidesde- itored with thermisters(Deban Enterprises,Inc.), and the tectedwith the HPLC systemduring the PEM-Tropics field pressurewasdeterminedwith an absolutepressuretransducer campaign.Other hydroperoxideswould have had to exceed (MKS InstrumentsCorp.)
L. Kok, Henry'slaw determinationsof hydrogen ChemicalStudies,Graduate Schoolof OceanographyU, niversityof peroxide,methylhydroperoxidea,nd peroxyaceticacid,J
Summary
The data setsusedfor thisperoxidedistributionwere from the NASA Global TroposphericExperiment,PacificExploratoryMissions(GTE-PEM). H202 and CH3OOH were the principalhydroperoxidesde- itored with thermisters(Deban Enterprises,Inc.), and the tectedwith the HPLC systemduring the PEM-Tropics field pressurewasdeterminedwith an absolutepressuretransducer campaign.Other hydroperoxideswould have had to exceed (MKS InstrumentsCorp.). The analyticalsystemwascomposedof a collectionsystemfor by passingthe air samplestream through a Hopcolite trap the gas phasehydroperoxidesa, nd the HPLC techniquede- (Mine Safety Appliance) and into the collectioncoil. Detectionlimitsfor H202 and CH3OOH West A and PEM-TropicsA field programsoccurredat the were and pptv,respectivel(y3 timesthe standarddevi- sametime of year Septemberto October, and PEM-West B ationof the blank).The estimatedaccuracyfor eachmeasure- occurredfrom Januaryto March, the differencesin the mean ment is available in the GTE database and was calculated mixing ratios of these speciesmay reflect seasonallydriven througha propagationof errors,roundedto the nearest changesin the species. The differentmissionsin a given2.5ø x 2.5ølatitude-longitude gridwere averagedin five altitudebins,0 , and
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