A WHO annual air quality guideline for sulphur dioxide (SO2) derived from WHO 24-hour guideline with data from seven cities

Abstract

BACKGROUND: WHO provided a short-term AQG for SO2 without provision of a corresponding annual limit. Short-term AQG are established for all criteria pollutants but only annual AQG are for particulate and nitrogen dioxide. Incomplete information for annual AQG limits may hinder the applicability and usefulness of guidelines in health impact assessment, risk communication and enforcement of regulations. OBJECTIVE: To assess the applicability estimating the annual AQG based on the WHO recommended short-term limit for SO2. METHODS: We obtained daily data for SO2 mass concentrations for years 2004 to 2010 from seven cities across Asia-Pacific, Europe and North America. We applied a lognormal probability distribution function to estimate the arithmetic mean to indicate the estimated annual AQG value by using the short-term guideline limit of 20?g/m3 as the maximum value in the model. RESULTS: The mean estimates of annual AQG from 2004 to 2010 in seven cities ranged from 3 to 6?g/m3. The pooled mean estimate is 5?g/m3 (95%CI:4-6) which was insensitive to adjustment for heterogeneity, extreme values, missing data, and number of monitors, as well as to statistical aggregation methods. CONCLUSIONS: The small difference in the estimated annual limit across seven cities provides good support for the adoption of 5?g/m3 as a proxy annual AQG which is statistically concordant with the short-term AQG of 20?g/m3. These findings are supported by our previous validation of WHO annual guideline limits using particulate matter data. They provide a useful model to evaluate health impact assessments and the validity for health protection of the currently recommended short-term interim targets for SO2 in different jurisdictions.