15:45 〜 16:00
[AAS09-20] Trends of formaldehyde and nitrogen dioxide as indicators of ozone sensitivity in megacities undergoing climate change
キーワード：Ozone pollution, Ozone precursors, Satellite observations, Megacities
Megacities are urban agglomerations with a population exceeding 10 million. There are currently 44 megacities worldwide, and projections indicate that the number will continue to increase in the coming years 1. During the last two decades, the urban population has significantly increased; over 55% of the global population lives in urban areas. Degraded air quality often characterizes urban areas, with ozone (O3) being one of the main issues. O3 is a secondary air pollutant that forms in the troposphere following a series of chemical reactions in which its main precursors, volatile organic compounds (VOC) and nitrogen oxides (NOx), play major roles. Thus, depending on their relative abundance, O3 formation can be either sensitive to VOC or NOx emissions 2. Megacities contain significant sources of precursors; hence, extreme O3 episodes are constant in several of the major urban areas of the planet, affecting a significant proportion of the global population. Since formaldehyde (HCHO) is a subproduct in the oxidation path of most of the emitted VOC, it has been widely used as an indicator species of VOC emissions. In this study, formaldehyde (HCHO) and nitrogen dioxide (NO2) column densities measured by the Ozone Monitoring Instrument (OMI) were used as a proxy for VOC and NOx emissions 3. A robust trend analysis was applied to evaluate the trend and magnitude changes from 2005 to 2019 and their ratios to assess the ozone formation sensitivity. The analysis focused on the 41 biggest urban agglomerations of the planet and four remote areas for comparison. A correlation analysis was conducted to evaluate the influence of the temperature and short-wave radiation on the O3 sensitivity trends. The results disclosed that VOC emissions significantly increased in all the analyzed regions, while NOx emissions showed spatial differences associated with their level of economic development. The ozone sensitivity classification indicated that the observed trends contradict the requirements for decreasing O3 in most analyzed sites, leading to increased or stagnated O3 levels. Furthermore, a strong correlation between increased precursor emissions and increasing temperatures suggests that O3 will continue to increase as global temperatures rise due to climate change.
References
1. Demographia. Demographia World Urban Areas (19th Edition). http://www.demographia.com/db-worldua.pdf (2023).
2. Sillman, S. The relation between ozone, NO(x) and hydrocarbons in urban and polluted rural environments. Atmospheric Environment vol. 33 1821–1845 Preprint at https://doi.org/10.1016/S1352-2310(98)00345-8 (1999).
3. Duncan, B. N. et al. Application of OMI observations to a space-based indicator of NOx and VOC controls on surface ozone formation. Atmos Environ 44, 2213–2223 (2010).
References
1. Demographia. Demographia World Urban Areas (19th Edition). http://www.demographia.com/db-worldua.pdf (2023).
2. Sillman, S. The relation between ozone, NO(x) and hydrocarbons in urban and polluted rural environments. Atmospheric Environment vol. 33 1821–1845 Preprint at https://doi.org/10.1016/S1352-2310(98)00345-8 (1999).
3. Duncan, B. N. et al. Application of OMI observations to a space-based indicator of NOx and VOC controls on surface ozone formation. Atmos Environ 44, 2213–2223 (2010).