Methyl Chloroform Continues to Constrain the Hydroxyl (OH) Variability in the Troposphere
Name
JGR Atmospheres - 2021 - Patra - Methyl Chloroform Continues to Constrain the Hydroxyl OH Variability in the Troposphere.pdf
Description
Published version
Size
1.7 MB
Format
Adobe PDF
Checksum (MD5)
25f2523db793638997a06d40e8769fc3
Author(s)
Patra, PK
Krol, MC
Prinn, RG
Takigawa, M
Mühle, J
Montzka, SA
Lal, S
Yamashita, Y
Naus, S
Chandra, N
Date Issued
February 27, 2021
Journal
Journal of Geophysical Research: Atmospheres
Publisher
American Geophysical Union
Citation
Patra, P. K., Krol, M. C., Prinn, R. G.,
Takigawa, M., Mühle, J., Montzka, S.
A., et al. (2021). Methyl chloroform
continues to constrain the hydroxyl (OH)
variability in the troposphere. Journal
of Geophysical Research: Atmospheres,
126, e2020JD033862.
Version
Final published version
Abstract
Trends and variability in tropospheric hydroxyl (OH) radicals influence budgets of many greenhouse gases, air pollutant species, and ozone depleting substances. Estimations of tropospheric OH trends and variability based on budget analysis of methyl chloroform (CH3CCl3) and process-based chemistry transport models often produce conflicting results. Here we use a previously tested transport model to simulate atmospheric CH3CCl3 for the period 1985–2018. Based on mismatches between model output and observations, we derive consistent anomalies in the inverse lifetime of CH3CCl3 (KG) using measurements from two independent observational networks (National Oceanic and Atmospheric Administration and Advanced Global Atmospheric Gases Experiment). Our method allows a separation between “physical” (transport, temperature) and “chemical” (i.e., abundance) influences on OH + CH3CCl3 reaction rate in the atmosphere. Small increases in KG due to “physical” influences are mostly driven by increases in the temperature-dependent reaction between OH and CH3CCl3 and resulted in a smoothly varying increase of 0.80% decade−1. Chemical effects on KG, linked to global changes in OH sources and sinks, show larger year-to-year variations (∼2%–3%), and have a negative correlation with the El Niño Southern Oscillation. A significant positive trend in KG can be derived after 2001, but it persists only through 2015 and only if we assume that CH3CCl3 emissions decayed more slowly over time than our best estimate suggests. If global CH3CCl3 emissions dropped below 3 Gg year−1 after 2015, recent CH3CCl3 measurements indicate that the 2015–2018 loss rate of CH3CCl3 due to reaction with OH is comparable to its value 2 decades ago.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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DOI of Published Version
10.1029/2020jd033862
