Relation Between High-Pressure Blocking and Aerosol Concentrations in Southern Sweden

High pressure weather is associated with atmospheric inversions, low wind speeds and little or no clouds and precipitation. High-pressure systems that stay stationary over a region for more than 5 days, called high-pressure blocking events, can cause elevated pollution levels due to the limited vertical mixing, and lack of aerosol removal through precipitation. In this study we have used meteorological and PM2.5 data from southern Sweden to investigate the evolution of pollution levels during high-pressure blocking events. We have used data from one rural and one urban station between 1995 and 2024. Moreover, we have used data from another meteorological station from between 1946 and 2024 to determine whether the frequency of high-pressure blocking events in the region is changing.

We find that the PM2.5 concentrations increase significantly during high pressure blocking events at both the rural and urban location. At both stations, the average increase is about 12 μgm^-3 over a 12-day period. The PM2.5 levels are however substantially higher at the urban station than at the rural station. After the high-pressure blocking events are terminated, the PM2.5 levels drop to lower levels within 1 day. The increase in PM2.5 levels during the blocking events is stronger when winds from the south east dominate the event and during events with a higher average pressure. The increase is also stronger during wintertime compared to summertime at the urban station. The analysis of high-pressure blocking frequency show that there is no significant change in the number of blocking events over the period 1946 to 2024 in this region. This study shows that high-pressure blocking events results in increasing PM2.5 levels in southern Sweden but that there is no increase in these types of events here.