13 Oct 2023
 | 13 Oct 2023

Identifying episodic carbon monoxide emission events in the MOPITT measurement dataset

Paul S. Jeffery, James R. Drummond, Jiansheng Zou, and Kaley A. Walker

Abstract. The Measurements Of Pollution In The Troposphere (MOPITT) instrument aboard NASA’s Terra satellite has been measuring upwelling radiance in a nadir-viewing mode since March 2000. These radiance measurements are inverted to yield estimates of carbon monoxide (CO) profiles and total columns, providing the longest satellite record of this trace gas to date. The CO measurements from MOPITT have been used in a variety of ways, including trend analyses and the construction of CO budgets. However, their use is complicated by the influence of episodic emission events, which release large quantities of CO into the atmosphere with irregular timing, such as large sporadic wildfires of natural or anthropogenic origin. The chaotic nature of these events is a large source of variability in CO budgets and models, requiring that these events be well characterized in order to develop an improved understanding of the role they have in influencing tropospheric CO. This study describes the development of a multi-step algorithm that is used to identify large episodic emission events using daily-mean Level 2 (L2) MOPITT total column measurements gridded to 0.5° by 0.5° spatial resolution. The core component of this procedure involves empirically determining the expectation density function (EDF) that describes the departure of daily-mean CO observations from the baseline behaviour of CO, as described by its periodic components and trends. The EDFs employed are not assumed to be symmetric, but instead are constructed from a pair of superimposed normal distributions. Enhancement flag files are produced following this methodology, identifying the episodic events that show strong enhancement of CO outside of the range of expected CO behaviour, and are now made available for the period 3 March 2000 to 31 July 2022. The distribution and frequency of these flagged measurements over this 22-year period is analyzed, to illustrate the robustness of this method.

Paul S. Jeffery et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2219', Shyno Susan John, 17 Nov 2023
  • RC2: 'Comment on egusphere-2023-2219', Anonymous Referee #2, 25 Nov 2023

Paul S. Jeffery et al.

Paul S. Jeffery et al.


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Short summary
The MOPITT instrument has been monitoring carbon monoxide (CO) since March 2000. This dataset has been used for many applications; however, episodic emission events, which release large amounts of CO into the atmosphere, are a major source of uncertainty. This study presents a method for identifying these events by determining measurements that are unlikely to have typically arisen. The distribution and frequency of these flagged measurements in the MOPITT dataset is presented and discussed.