BayCEER Workshop 2022

Investigation of the Non-Linear Tropospheric Ozone Production Along an Urban - Rural Gradient

P 4.3 in Poster Session

To reduce tropospheric ozone production and improve air quality, the precursor compounds nitrogen oxides and aromatic volatiles have been regulated in many states worldwide for several decades. Despite the successful reduction of these precursors, tropospheric ozone in urban and suburban areas exhibits positive, rising trends. These observations are caused by complex and non-linear ozone photochemistry, which is not fully understood to date.

Here, the temporal and spatial ozone trends and their regulated precursors were analyzed over the last 30 years. Additionally, the content of volatile organic compounds (VOC) in the air at contrasting locations was determined using thermal-desorption gas chromatography. We selected these measurement sites in Bavaria (Germany) based on their degree of urbanization and population, resulting in three categories: Urban, Suburban and Rural areas.

It was shown that in urban ambient air nitrogen monoxide decreased at a rate of 1.6 µg/m³ per year over the course of the last 30 years, whereas ozone concentrations increased about 0.5 µg/m³ annually. Similar behavior could also be detected in suburban areas with a decrease in nitrogen monoxide of 0.9 µg/m³ per year and an ozone increase of 0.5 µg/m³. In contrast, at a site located remotely, stagnating low levels of nitrogen oxides and persistently high levels of ozone reaching more than 100 µg/m³ during the summer 2022 were observed. For further analysis, we combined spatial and temporal scales to bridge over long-term trends (decades), seasons, weekly and diurnal variability, and to highlight dependencies on the underlying chemical mechanisms regarding regional and local contributions to ozone production.

Keywords: Tropospheric Ozonechemistry, Photochemistry, Data analysis