Establishment of Long-Term Measurement of Alkali-Containing Particles at The Natrium Air Quality Research Station

Abstract

Measurement of alkali-containing aerosol particles over extended periods provides valuable insight into both natural and anthropogenic influences on air quality. This study aimed to establish continuous measurement of alkali-containing particles using a Surface Ionization Detector (SID) at the Natrium Air Quality Research Station in Gothenburg. As a low-cost with high-impact tool, the SID holds strong potential for long-term atmospheric research. The project focused on optimizing SID operational parameters, characterizing the temporal variability of alkali particles, and comparing results with complementary datasets, including EDXRF filter analysis and PM2.5 measurements. In total 40 days of valid data were obtained from a 62-day measurement campaign. SID measurements revealed that alkali particle concentrations were influenced by meteorological conditions and air mass origins. Results from EDXRF analysis shows that on some occasion, EDXRF detected high chlorine levels during a short sampling period in February. However, alkali concentration was low possibly due to incomplete data and different temporal resolution. In contrast, during April, SID concentrations aligned more closely with EDXRF results. These elevated levels were also observed during mild temperatures and periods of high relative humidity, likely associated with sodium from sea salt particles in marine air. Lower concentrations occurred under colder conditions and easterly winds, suggesting potassium-containing particle from inland biomass burning influence. Back trajectory analysis using the HYSPLIT model further supported these findings, showing that the highest alkali concentrations were linked to Atlantic air masses, while the most frequent easterly inland flows exhibited the lowest concentrations. This emphasises the role of sea salt as a major contributor and highlights the importance of air mass transport in shaping ambient alkali-containing aerosol levels. Overall, this study demonstrates SID’s effectiveness as a selective, sensitive instrument for detecting trace alkali species and offers valuable insights for future aerosol monitoring.