Improving Our Understanding of Arctic Tropospheric Pollution Through Measurements and Models

In this thesis, ground-based Fourier transform infrared (FTIR) measurements from the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut are used to retrieve total columns of CO, C2H2, C2H4, C2H6, CH3OH, HCOOH, H2CO, and PAN over the period of 2006--2020. The retrievals of C2H4 and PAN were developed as part of this thesis, and are the first long-term ground-based FTIR measurements of these gases in the high Arctic. A global inter-comparison of the TROPOMI and ACE-FTS CO satellite datasets shows strong correlations but a latitudinal dependence of the biases, with positive biases in high-latitude regions and negative biases near the equator. At Eureka, the TROPOMI CO total columns were highly correlated with the ground-based FTIR measurements but with a mean bias of 14.7 +- 0.16%. ACE-FTS and the FTIR CO partial columns show good correlations and a mean bias of 7.89 +- 0.21%. All mean TROPOMI biases fall within the TROPOMI mission accuracy requirement. FTIR measurements of CO, C2H4, CH3OH, HCOOH, and PAN at Eureka were strongly enhanced in August 2017 due to wildfires in British Columbia and the Northwest Territories. For CO, C2H4, HCOOH, and PAN, these were the largest observed enhancements at Eureka. The emissions of these fires were estimated using FTIR and IASI measurements at Eureka, and for C2H4 and HCOOH they were found to be higher than previously reported. The fires were also simulated using the GEOS-Chem model, and the impact of the modeled biomass burning injection height and secondary VOC production was investigated. The inter- and intra-annual variability of the eight trace gases were derived from FTIR measurements at Eureka, Nunavut (2006--2020) and Thule, Greenland (1999--2022). Consistent seasonal cycles were observed at both sites. Decreasing trends were observed for CO, C2H2, and CH3OH at both sites, and for HCOOH at Eureka. Increasing trends were detected for C2H6 and H2CO at both sites, and for PAN at Eureka. A GEOS-Chem simulation for 2003--2021 was performed. The model reproduced the seasonality of all gases, but showed large negative biases for some species. The modeled trends broadly agreed with observations for all species except C2H6, H2CO, and PAN.

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