Short-Term Associations between PM₁₀ and Respiratory Health Effects in Visby, Sweden

The old Swedish city Visby, located on the island Gotland, has, for several years, reported higher PM₁₀ concentrations than any other city in Sweden. In Visby, local limestone is used, both in road paving and as sand used for anti-slip measures, resulting in a clear annual pattern of PM₁₀ with the highest concentrations during winter/spring when studded tires are allowed. This study analyzes the short-term associations between PM₁₀ and daily number of patients with acute respiratory problems (ICD-10 diagnoses: J00-J99) seeking care at the hospital or primary healthcare units in Visby during the period of 2013-2019. The daily mean of PM₁₀ was on average 45 µg m^-3 during winter/spring and 18 µg m^-3 during summer/autumn. Four outcome categories were analyzed using quasi-Poisson regression models, stratifying for period and adjusting for calendar variables and weather. An increase in respiratory visits was associated with increasing concentrations in PM₁₀ during the summer/autumn period, most prominent among children, where asthma visits increased by 5% (95% CI: 2-9%) per 10 µg m^-3 increase in PM₁₀. For the winter/spring period, no significant effects were observed, except for the diagnose group 'upper airways' in adults, where respiratory visits increased by 1% (95% CI: 0.1-1.9%) per 10 µg m^-3 increase. According to the results, limestone in particles seem to be relatively harmless at the exposure concentrations observed in Visby, and this is in line with the results from a few experimental and occupational studies.