BackgroundSeveral observational studies have suggested that outdoor air pollution may induce or aggravate asthma. However, epidemiological results are inconclusive due to the presence of numerous moderators which influence this association. The goal of this study was to assess the relationship between outdoor air pollutants and moderate or severe asthma exacerbations in children and adults through a systematic review and multilevel meta-analysis.Material and methodsWe searched studies published in English on PubMed, Scopus, and Google Scholar between January 2000 and October 2016. Studies following a case-crossover design with records of emergency departments and/or hospital admissions as a surrogate of moderate or severe asthma exacerbations were selected. A multilevel meta-analysis was employed, taking into account the potential clustering effects within studies examining more than one lag. Odds ratios (ORs) and 95% confidence intervals were estimated. A subgroup analysis in children aged 0 to 18 years and a sensitivity analysis based on the quality of the included studies as defined in the Newcastle-Ottawa Scale were performed. Publication bias was evaluated through visual inspection of funnel plots and by a complementary search of grey literature. (Prospero Registration number CRD42015032323).ResultsDatabase searches retrieved 208 records, and finally 22 studies were selected for quantitative analysis. All pollutants except SO2 and PM10 showed a significant association with asthma exacerbations (NO2: 1.024; 95% CI: 1.005,1.043, SO2: 1.039; 95% CI: 0.988,1.094), PM10: 1.024; 95% CI: 0.995,1.053, PM2.5: 1.028; 95% CI: 1.009,1.047, CO: 1.045; 95% CI: 1.005,1.086, O3: 1.032; 95% CI: 1.005,1.060. In children, the association was significant for NO2, SO2 and PM2.5.ConclusionThis meta-analysis provides evidence of the association between selected air pollutants and asthma exacerbations for different lags.

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Modern diagnostic meteorological models such as CALMET parameterise slope flows, kinematic terrain effects, terrain blocking effects, and include a divergence minimisation procedure. They also contain a micrometeorological model for the calculation of the planetary boundary-layer parameters both over-land and over-water. In CALMET, in particular, the energy balance equation gives the total contribution of direct and diffuse solar radiation reaching the ground, and topography shading is not accounted for.However, especially in the case of very complex terrain, topography shading generally has important effects on the energy balance, and as a consequence, on the flow field. Also, air temperature at the ground depends on the altitude above sea level, and interpolation of sparse measurements on a regular domain grid should account for this.We present algorithms that should improve the description of the physical effects mentioned above, through the independent calculation of direct, diffuse and reflected components of shortwave radiation, the consideration of the air temperature vertical gradient and vegetation cover for the interpolation of surface temperature observations, and the evaluation of the position of the Sun and topography slope and aspect.These algorithms, of general application, were implemented into CALMET to evaluate, qualitatively and against measurements, their performance on a very complex Alpine domain in northern Italy.CALMET was chosen since it is the diagnostic meteorological model of the CALPUFF modelling system. CALPUFF is recommended by the United States Environmental Protection Agency (US-EPA) as the preferred model for long-range transport in general, and for shorter distances on a case-by-case basis.