MOPITT CO and MODIS AOD Trend Analysis

Measurements Of Pollution In The Troposphere (MOPITT) has been measuring atmospheric carbon monoxide (CO) from space for two decades. This valuable long-term record from a single consistent instrument allows for analysis of atmospheric variability and trends. Similar to Worden et al. (2013), we find that CO has been decreasing globally for the last two decades. However, we find a global slowdown in the rate compared with the previous analysis. Aerosols are co-emitted with CO from both fires and anthropogenic sources, and have a shorter chemical lifetime. Consequently, combined trend analyses of CO and aerosol optical depth (AOD) can help elucidate the drivers of regional differences in the CO trend. We use the AOD measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument to help understand regional differences in the CO trends.

Residual trends (trend - global average trend) in column CO (left) and trends in AOD (right) between 2002 and 2018
Figure 1. Residual trends (trend - global average trend) in column CO (left) and trends in AOD (right) between 2002 and 2018, aggregated to a 1x1 degree grid. The 19 sub-regions of interest are overlaid on the AOD trend plot. Click for larger image.

Our analysis splits the CO and AOD records into two time periods (2002-2009 and 2010-2018) and 19 sub-regions, as well as performs trend calculations on monthly percentile values for CO. We also perform a complete systematic and random uncertainty analysis on the CO trends to quantify the trend robustness. We suggest that recent positive trends in fire activities in Northern Hemisphere boreal regions may have contributed to the slowing down of decreasing CO. Additionally, time-varying air quality control policies will have different impacts on atmospheric composition and related trends. Anthropogenic regions with minimal air quality management such as North India will likely have greater global impact as the global CO trend weakens.

Our study includes satellite measurements of CO from four other satellite instruments, making this a highly collaborative cross-institutional project. The publication being prepared from this research will contribute to the Terra satellite 20-year special collection in the Remote Sensing of Environment (RSE) journal, as well as to the 6th Assessment Report (AR6) of the United Nations Intergovernmental Panel on Climate Change IPCC.

References

Worden, H M, M N Deeter, C Frankenberg, M George, F Nichitiu, J Worden, I Aben, et al. 2013. “Decadal Record of Satellite Carbon Monoxide Observations.” Atmospheric Chemistry and Physics 13: 837–50.