Abstract
Measurements of hydroxyl radical (OH), sulfuric acid (H2SO4), and methane sulfonic acid (MSA) were performed aboard the NASA P‐3B using the selected ion chemical ionization mass spectrometry technique during the Transport and Chemical Evolution over the Pacific (TRACE‐P) study. Photochemical box model calculations of OH concentrations yielded generally good agreement with an overall tendency to overestimate the measured OH by ∼20%. Further analysis reveals that this overestimation is present only at altitudes greater than ∼1.5 km, with the model underestimating OH measurements at lower altitudes. Boundary layer H2SO4 measurements, performed in a volcanic plume off the southern coast of Japan, revealed some of the largest marine boundary layer H2SO4 concentrations ever observed and were accompanied by new particle formation. Nighttime measurements of OH, H2SO4, and MSA in the remote pacific off Midway Island revealed significant boundary layer concentrations of H2SO4 and MSA, indicating evidence of nighttime boundary layer oxidation processes but in the absence of OH. A cursory exploration of the sources of production of the H2SO4 and MSA observed at night is presented.
Highlights
[2] The NASA Global Tropospheric Experiment (GTE) Transport and Chemical Evolution over the Pacific (TRACE-P) study offered a unique opportunity to perform OH, H2SO4, and methane sulfonic acid (MSA) measurements over a wide variety of environments and conditions
[6] Here we present highlights of OH, H2SO4, and MSA measurements made aboard the NASA P-3B during the TRACE-P study
[15] The results of OH, H2SO4, and MSA measurements performed aboard the P-3B during TRACE-P can be found in the GTE data archive at http://www-gte.larc.nasa.gov/ trace/TP_dat.htm
Summary
Photochemical box model calculations of OH concentrations yielded generally good agreement with an overall tendency to overestimate the measured OH by $20%. Further analysis reveals that this overestimation is present only at altitudes greater than $1.5 km, with the model underestimating OH measurements at lower altitudes. Boundary layer H2SO4 measurements, performed in a volcanic plume off the southern coast of Japan, revealed some of the largest marine boundary layer H2SO4 concentrations ever observed and were accompanied by new particle formation. Nighttime measurements of OH, H2SO4, and MSA in the remote pacific off Midway Island revealed significant boundary layer concentrations of H2SO4 and MSA, indicating evidence of nighttime boundary layer oxidation processes but in the absence of OH.
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