1Brookhaven National Laboratory, Atmospheric Sciences Division, Upton, NY 11973, USA
2Chemistry/Physics Department, State University of New York, Old Westbury, NY 11568, USA
3Rosenstiel School of Marine and Atmospheric Science, Div. of Marine and Atmospheric Chemistry, Univ. of Miami, Miami, FL 33149, USA
4University of Arkansas, Department of Chemistry, Little Rock, AR 72204, USA
5Georgia Inst. of Technol., School of Earth & Atmospheric Sciences, Atlanta, GA 30332, USA
Abstract. Mixing ratios of hydrogen peroxide and hydroxymethyl hydroperoxide were determined aboard the US Department of Energy G-1 Research Aircraft during the March 2006 MILAGRO field campaign in Mexico. Ground measurements of total hydroperoxide were made at the T1 site at Universidad Technologica de Tecámac, about 35 km NW of Mexico City. In the air and on the ground, peroxide mixing ratios near the source region were generally near 1 ppbv, much lower than had been predicted from photochemical models based on the 2003 Mexico City study. Strong southerly flow resulted in transport of pollutants from the T0 to T1 and T2 surface sites on several flight days. On these days, it was observed that peroxide concentrations slightly decreased as the G-1 flew progressively downwind. This observation is consistent with low or negative net peroxide production rates calculated for the source region and is due to the very high NOx concentrations above the Mexico City plateau. However, relatively high values of peroxide were observed at takeoff and landing near Veracruz, a site with much higher humidity and lower NOx concentrations.