Large-scale distributions of tropospheric nitric, formic, and acetic acids over the western Pacific basin during wintertime

Authors

R. Talbot, University of New HampshireFollow
Jack E. Dibb, University of New HampshireFollow
Barry Lefer, University of Houston - Main
Eric Scheuer, University of New Hampshire - Main CampusFollow
J D. Bradshaw, Georgia Institute of Technology - Main Campus
S T. Sandholm, Georgia Institute of Technology
S Smyth, University of California, Irvine
D R. Blake, University of California, Irvine
N J. Blake, University of California, IrvineFollow
G W. Sachse, NASA Langley Research CenterFollow
J E. Collins Jr, Science and Technology Corp
G L. Gregory, NASA

Abstract

We report here measurements of the acidic gases nitric (HNO₃), formic (HCOOH), and acetic (CH₃COOH) over the western Pacific basin during the February-March 1994 Pacific Exploratory Mission-West (PEM-West B). These data were obtained aboard the NASA DC-8 research aircraft as it flew missions in the altitude range of 0.3–12.5 km over equatorial regions near Guam and then further westward encompassing the entire Pacific Rim arc. Aged marine air over the equatorial Pacific generally exhibited mixing ratios of acidic gases <100 parts per trillion by volume (pptv). Near the Asian continent, discrete plumes encountered below 6 km altitude contained up to 8 parts per billion by volume (ppbv) HNO₃ and 10 ppbv HCOOH and CH₃COOH. Overall there was a general correlation between mixing ratios of acidic gases with those of CO, C₂H₂, and C₂Cl₄, indicative of emissions from combustion and industrial sources. The latitudinal distributions of HNO₃ and CO showed that the largest mixing ratios were centered around 15°N, while HCOOH, CH₃COOH, and C₂Cl₄ peaked at 25°N. The mixing ratios of HCOOH and CH₃COOH were highly correlated (r² = 0.87) below 6 km altitude, with a slope (0.89) characteristic of the nongrowing season at midlatitudes in the northern hemisphere. Above 6 km altitude, HCOOH and CH₃COOH were marginally correlated (r² = 0.50), and plumes well defined by CO, C₂H₂, and C₂Cl₄ were depleted in acidic gases, most likely due to scavenging during vertical transport of air masses through convective cloud systems over the Asian continent. In stratospheric air masses, HNO₃ mixing ratios were several parts per billion by volume (ppbv), yielding relationships with O₃ and N₂O consistent with those previously reported for NO_y.

Department

Earth Sciences, Earth Systems Research Center

Publication Date

12-20-1997

Journal Title

Journal of Geophysical Research: Atmospheres

Publisher

Wiley

Digital Object Identifier (DOI)

10.1029/96JD02975

Document Type

Article

Recommended Citation

Talbot, R. W., et al. (1997), Large-scale distributions of tropospheric nitric, formic, and acetic acids over the western Pacific basin during wintertime, J. Geophys. Res., 102(D23), 28303–28313, doi:10.1029/96JD02975.

Rights

Copyright 1997 by the American Geophysical Union.