Carbon monoxide balance in nature.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Geochemistry

Background:

• Carbon monoxide (CO) is a significant atmospheric pollutant with complex sources and sinks.
• Previous estimates of CO production rates, primarily from combustion, may have underestimated its overall atmospheric burden.
• Understanding CO's atmospheric cycle is crucial for climate modeling and air quality assessments.

Purpose of the Study:

• To determine the total production rate of carbon monoxide in the troposphere.
• To investigate the role of methane oxidation and hydroxyl radicals in the tropospheric carbon monoxide cycle.
• To estimate the residence time of carbon monoxide in the troposphere.

Main Methods:

• Utilized steady-state equations for both stable and radioactive carbon monoxide.
• Calculated carbon monoxide production rates based on atmospheric residence times.
• Assessed the contribution of methane oxidation and hydroxyl radical reactions to CO production and removal.

Main Results:

• Carbon monoxide is produced at a rate of 5x10^15 grams per year, approximately 25 times greater than combustion-derived estimates.
• The estimated residence time for carbon monoxide in the troposphere is 0.1 year.
• Hydroxyl radicals are identified as the key species responsible for both the production of CO via methane oxidation and its removal via CO oxidation.

Conclusions:

• Methane oxidation is a dominant, previously underestimated source of tropospheric carbon monoxide.
• The calculated hydroxyl radical concentration (2.3x10^6 molecules/cm³) supports the proposed CO production and removal model.
• The findings align with independent photochemical deductions of hydroxyl radical concentrations, validating the atmospheric model.