Pollution trapping by strong temperature inversions in Fairbanks, Alaska

Cesler-Maloney, Meeta V.

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Author

Cesler-Maloney, Meeta V.

Chair

Simpson, William R.
Mao, Jingqiu

Committee

Guerard, Jennifer
Stuefer, Martin

Abstract

In cold climates during winter, surface-based temperature inversions reduce vertical dispersion within the atmospheric boundary layer. Reduced vertical dispersion coupled with stagnant horizontal winds causes pollution emitted near the ground level to accumulate to unhealthy amounts. To study pollution trapping, we measured vertical differences in fine particulate matter and ozone across a shallow 20-meter vertical scale during surface-based inversions in Fairbanks, Alaska and showed that pollution trapping occurs on this extremely shallow scale. In winter 2022, trace gases were measured by long-path differential absorption spectroscopy to probe vertical dispersion on a taller scale, up to ~200 m above the surface. We added horizontal dispersion to a one-dimensional Eulerian chemical transport model and used the model with both vertical and horizontal dispersion, but without chemistry, to simulate the vertically resolved measurements of SO₂. The model achieved excellent results with correlation to the observations having a coefficient of R = 0.88. Steady-state transport residence times calculated from the model were on the order of hours, indicating limited time for chemical processing during winter in Fairbanks. Within the model, only ground-based emissions sources were included and there was no interaction between air above and below the boundary layer height, suggesting that ground-based sources dominate pollution measured at ground level. With the knowledge that ground level sources have a large impact on pollution, we carried out an analysis of trace gases and fine particulate matter measured near ground level that was used to better understand the response to pollution control strategies in Fairbanks. This analysis shows that the total amount of pollution in Fairbanks has been trending down over the past nine years. Following a September 2022 legal change that mandated lower sulfur content in heating oil, the amount of sulfur dioxide gas dropped significantly during winter 2022-2023 as compared to the prior three-year average.

Description

Dissertation (Ph.D.) University of Alaska Fairbanks, 2023

Chapter 1: Introduction -- 1.1 Motivations -- 1.2 Atmospheric dispersion within the stable boundary layer -- 1.3 Wintertime pollution trapping in urban areas -- 1.4 History of PM2.5 pollution in Fairbanks, Alaska -- 1.5 Background on pollution mitigation efforts in Fairbanks, Alaska -- 1.6 Structure of dissertation -- 1.7 References. Chapter 2: Differences in ozone and particulate matter between ground level and 20 m aloft are frequent during wintertime surface-based temperature inversions in Fairbanks, Alaska -- 2.1. Introduction -- 2.2. Methods -- 2.2.1. Measurements of PM₂.₅ and O₃ and temperature -- 2.2.2. Calibration and quality control for measurements -- 2.3. Results -- 2.3.1. Characteristics of SBIs and influence on surface PM₂.₅ concentrations -- 2.3.2. Differences in PM₂.₅ concentration with altitude -- 2.3.3. Differences in O₃ with altitude -- 2.4. Discussion -- 2.4.1. Characteristics of SBIs in Fairbanks -- 2.4.2. Differences of PM at the CTC building and trailer tower -- 2.4.3. Influence of SBIs on PM₂.₅ and O₃ differences -- 2.5. Conclusion -- 2.6. Data availability statement -- 2.7. Acknowledgements -- 2.8. References -- 2.9. Tables -- 2.10. Figures. Chapter 3: Shallow boundary layer heights controlled by the surface-based temperature inversion strength are responsible for trapping home-heating emissions near the ground level in Fairbanks, Alaska -- 3.1 Introduction -- 3.2 Field measurements from the ALPACA campaign -- 3.3 Methods -- 3.3.1 Description of the PACT-1D model -- 3.3.2 Treatment of vertical exchange -- 3.3.3 Treatment of horizontal exchange -- 3.3.4 Treatment of emissions -- 3.3.5 Diagnosing vertical and horizontal exchange -- 3.3.6 Diagnosing steady state residence times for vertical and horizontal loss processes -- 3.4 Results -- 3.4.1 Conceptual model for pollution trapping in Fairbanks -- 3.4.2 Observations and modeling for the ALPACA campaign -- 3.4.3 Correlation of Model to LP-DOAS SO₂ -- 3.4.4 Model steady state transport residence times during ALPACA -- 3.5 Discussion -- 3.5.1 Relationship between steady state vertical profile shape and SBL height -- 3.5.2 Relationship between pollution trapping and temperature inversion strength -- 3.5.3 Skill of PACT-1D in modeling observed SO₂ vertical profiles -- 3.5.4 Model sensitivity studies -- 3.5.5 Analysis of modeled steady state transport residence times -- 3.6 Conclusion -- 3.7 Data availability -- 3.8 Acknowledgements -- 3.10 Tables -- 3.11 Figures. Chapter 4: Changes to ground level pollution in Fairbanks, Alaska in response to pollution regulations -- 4.1 Introduction -- 4.2 Methods -- 4.2.1 Data retrieval -- 4.2.2 Internal quality assurance procedure -- 4.2.3 Sulfur Oxidation Ratio calculation -- 4.3 Results -- 4.4 Discussion -- 4.5 Conclusion -- 4.6 References -- 4.7 Figures. Chapter 5: Conclusion and Future Directions -- 5.1 Conclusions -- 5.2 Future directions -- 5.3 References.

Date

2023-12

Type

Dissertation

Collections

Chemistry and Biochemistry