To investigate the association between Saharan dust outbreaks and natural, cardiovascular and respiratory mortality.MethodsA case–crossover design was adopted to assess the effects of Saharan dust days (SDD) on mortality in the Emilia-Romagna region of Italy. The population under study consisted of residents in the six main towns of the central-western part of the region who died between August 2002 and December 2006. The association of Saharan dust outbreaks and PM10 concentration with mortality was estimated using conditional logistic regression, adjusted for apparent temperature, holidays, summer population decrease, flu epidemic weeks and heat wave days. The role of the interaction term between PM10 and SDD was analysed to test for effect modification induced by SDD on the PM10-mortality concentration–response function. Separate estimates were undertaken for hot and cold seasons. We found some evidence of increased respiratory mortality for people aged 75 or older on SDD. Respiratory mortality increased by 22.0% (95% CI 4.0% to 43.1%) on the SDD in the whole year model and by 33.9% (8.4% to 65.4%) in the hot season model. Effects substantially attenuated for natural and cardiovascular mortality with ORs of 1.042 (95% CI 0.992 to 1.095) and 1.043 (95% CI 0.969 to 1.122), respectively.ConclusionsOur findings suggest an association between respiratory mortality in the elderly and Saharan dust outbreaks. We found no evidence of an effect modification of dust events on the concentration–response relationship between PM10 and daily deaths. Further work should be carried out to clarify the mechanism of action.

In this paper we present a study on stratospheric intrusion (SI) events recorded at a high mountain station in the Italian northern Apennines. Six years (1998–2003) of surface ozone and beryllium-7 concentration measurements as well as relative humidity values recorded at the GAW Mt. Cimone research station (44°11'N, 10°42'E; 2165 m asl) were analyzed. Moreover, three-dimensional backward trajectories calculated by the FLEXTRA model and potential vorticity values along these trajectories were used. In order to identify SI and evaluate their contribution to the tropospheric ozone at Mt. Cimone, a statistical methodology was developed. This methodology consists of different selection criteria based on observed and modeled stratospheric tracers as well as on tropopause height values recorded by radio soundings. On average, SI effects affected Mt. Cimone for about 36 days/year. The obtained 6-year SI climatology showed a clear seasonal cycle with a winter maximum and a spring-summer minimum. The seasonal cycle was also characterized by an interannual variation. In particular, during winter (autumn), SI frequency could be related to the intensity of the positive (negative) NAO phase. In order to separate direct SI from indirect SI, a restrictive selection criterion was set. This criterion, named Direct Intrusion Criterion (DIC), requested that all the analyzed tracers were characterized by stratospheric values. Direct SI affected Mt. Cimone for about 6 days/year, with frequency peaks in winter and early summer. At Mt. Cimone, SI contribution to background ozone concentrations was largest in winter. On average, an ozone increase of 8% (3%) with respect to the monthly running mean was found during direct (indirect) SI. Finally, the typical variations of stratospheric tracers during SI events were analyzed. The analysis of in situ atmospheric pressure values suggested that direct SI were connected with intense fronts affecting the region, while indirect SI were possibly connected with subsiding structures related with anticyclonic areas.

We report chemical composition data for PM10 and PM1 from the Nepal Climate Observatory-Pyramid (NCO-P), the world's highest aerosol observatory, located at 5079 m a.s.l. at the foothills of Mt. Everest. Despite its high altitude, the average PM10 mass apportioned by the chemical analyses is of the order of 6µg m-3 (i.e., 10 µg/scm), with almost a half of this mass accounted for by organic matter, elemental carbon (EC) and inorganic ions, the rest being mineral dust. Organic matter, in particular, accounted for by 2.0 µg m-3 (i.e., 3.6µg/scm) on a yearly basis, and it is by far the major PM10 component beside mineral oxides. Non-negligible concentrations of EC were also observed (0.36 µg/scm), confirming that light-absorbing aerosol produced from combustion sources can be efficiently transported up the altitudes of Himalayan glaciers. The concentrations of carbonaceous and ionic aerosols follow a common time trend with a maximum in the premonsoon season, a minimum during the monsoon and a slow recovery during the postmonsoon and dry seasons, which is the same phenomenology observed for other Nepalese Himalayan sites in previous studies. Such seasonal cycle can be explained by the seasonal variations of dry and moist convection and of wet scavenging processes characterizing the climate of north Indian subcontinent. We document the effect of orographic transport of carbonaceous and sulphate particles upslope the Himalayas, showing that the valley breeze circulation, which is almost permanently active during the out-of-monsoon season, greatly impacts the chemical composition of PM10 and PM1 in the high Himalayas and provides an efficient mechanism for bringing anthropogenic aerosols into the Asian upper troposphere (>5000 m a.s.l.). The concentrations of mineral dust are impacted to a smaller extent by valley breezes and follow a unique seasonal cycle which suggest multiple source areas in central and south-west Asia. Our findings, based on two years of observations of the aerosol chemical composition, provide clear evidence that the southern side of the high Himalayas is impacted by transport of anthropogenic aerosols which constitute the Asian brown cloud.