Seasonal Mediterranean pattern for airborne spores of Alternaria

Airborne Alternaria spore presence depends in part on temperature and most studies claim that the highest values are found in summer. Such pattern, however, does not match in Mediterranean countries. The aim of present work is to study the pattern of airborne Alternaria in three places in the SW of Spain and to study the influence of meteorological factor in each station. Data of airborne spore concentration for a total of five different years study period, in three cities in the SW of Spain—Badajoz, Cáceres and Mérida—are provided in the present work. Continuous sampling was carried out using a Hirst volumetric spore trap in each location. Results were analyzed taking into account weather parameters regarding temperature, rain and relative humidity. Average concentration accounting for the complete data set (i.e. considering three locations and full time period) approached 50 spores/m3. Although Alternaria spores are present nearly throughout the whole year, monthly data showed that on three occasions October was the month with the highest monthly concentrations—up to 342 spores/m3, and January and February those with the lowest concentrations—when even no spores were recorded. Daily data showed a concentration peak of 1,380 spores/m3 in Mérida in October. Annual spore concentration showed a pronounced seasonality, with a first maximum concentration in autumn, mainly in October, and a second peak in spring, mainly in May and June. A clear drop was observed in summer, but values remained around the annual average concentration. Data of spore concentration showed statistically significant positive correlation with temperature and statistically significant negative correlation with rain and relative humidity. Monthly concentration of Alternaria spores was positively affected by temperature and negatively affected by relative humidity and rain; nevertheless, the decrease of relative humidity below 55% showed a drop in spore concentration regardless of any increase in temperature.