Influence of atmospheric circulation patterns on urban air quality during the winter

摘要

Relationships between urban nitrogen dioxide (NO₂) and atmospheric circulation at two spatial scales were studied for Southern Sweden. Lamb Weather Types (LWT) describe the circulation (scale: thousands of kilometers) including non–directional (cyclonic and anticyclonic) and directional types depending on the wind direction. LWTs with low wind speeds (anticyclonic, NW and N) were associated with strongly elevated [NO₂], between 46–52% of the daily averages of NO₂ exceeded the 60 μg m−3 air quality standard (AQS) when occurring during these LWTs. The lowest fractions of exceedances of NO₂ AQS were generally observed for LWTs E, S, SW and W. A larger scale circulation (several thousands of kilometers) was represented by the North Atlantic Oscillation (NAO) affecting meteorology over middle and high latitudes in the Northern Hemisphere. While a negative NAO index (NAOI) favors stagnant high pressure weather over Northern Europe, a positive NAOI is often associated with windy conditions. High [NO₂] was found to be frequent under negative NAOI. Additionally, larger fractions of exceedances of NO₂ AQS were observed for the majority of LWTs occurring at negative NAOI. It’s concluded that both LWTs and NAOI had partly independent effects on the urban air quality in a North European city. These circulation indices can be useful tools for air pollution risk assessment and forecasting.