Mortality risks due to long-term ambient sulphur dioxide exposure: large variability of relative risk in the literature.

Several studies have been published about the potential health effects due to long-term exposure to sulphur dioxide (SO2) and the relative risks (RRs) for different causes of mortality. Broad differences in the RR values are found, however. In this study, we performed an analysis of these studies aiming finding potential explanations for the high variability of the RR reported. The RRs for stratified subgroups were also analysed to identify more susceptible subgroups. A total of 14 studies were identified. Some of them related strong associations between mortality and long-term ambient SO2 exposure, while others found insignificant or no associations to the same mortality indexes. The mean RR values ranged from 0.95 to 1.14 for mortality due to all causes, 0.99 to 3.05 for lung cancer, 0.87 to 1.3 for respiratory diseases, 0.96 to 1.14 cardiovascular diseases and 0.97 to 1.05 for cardiopulmonary diseases mortality. Among the factors that may affect the RR estimations, only the size of studied population and the spatial scales used in exposure assessment showed notable influences. The female population was found to be more susceptible to long-term SO2 exposure. For other stratified subgroups including age, smoking status and income levels, no obvious relationship with RR was observed.

Analysis of PM2.5 concentrations under pollutant emission control strategies in the metropolitan area of São Paulo, Brazil.

Great efforts have been made over the years to assess the effectiveness of air pollution controls in place in the metropolitan area of São Paulo (MASP), Brazil. In this work, the community multiscale air quality (CMAQ) model was used to evaluate the efficacy of emission control strategies in MASP, considering the spatial and temporal variability of fine particle concentration. Seven different emission scenarios were modeled to assess the relationship between the emission of precursors and ambient aerosol concentration, including a baseline emission inventory, and six sensitivity scenarios with emission reductions in relation to the baseline inventory: a 50% reduction in SO2 emissions; no SO2 emissions; a 50% reduction in SO2, NOx, and NH3 emissions; no sulfate (PSO4) particle emissions; no PSO4 and nitrate (PNO3) particle emissions; and no PNO3 emissions. Results show that ambient PM2.5 behavior is not linearly dependent on the emission of precursors. Variation levels in PM2.5 concentrations did not correspond to the reduction ratios applied to precursor emissions, mainly due to the contribution of organic and elemental carbon, and other secondary organic aerosol species. Reductions in SO2 emissions are less likely to be effective at reducing PM2.5 concentrations at the expected rate in many locations of the MASP. The largest reduction in ambient PM2.5 was obtained with the scenario that considered a reduction in 50% of SO2, NOx, and NH3 emissions (1 to 2 µg/m3 on average). It highlights the importance of considering the role of secondary organic aerosols and black carbon in the design of effective policies for ambient PM2.5 concentration control.