Analysis of the evolution of gross alpha and gross beta activities in airborne samples in Valencia (Spain).

Gross alpha (Aα ) and gross beta activities (Aβ ) were measured weekly in the airborne of the Universitat Politècnica de Valencia campus (in the east of Spain) during the period 2009-2015 (7 years). The geometric mean values of weekly Aα and Aβ were 0.53·10-4 Bq m-3 and 5.77·10-4 Bq m-3 , respectively; with an average ratio Aα /Aβ of 0.097. This study highlights the heterogeneity of gross alpha and gross beta activities depending on the different periods of the year. Data show seasonal variations with the highest activity in summer months and the lowest one in winter months. Several atmospheric factors were considered in order to explain this intra-annual variation (wind speed, temperature, relative humidity, precipitations, dust content and prevailing wind directions). Multiple Linear Regression Analysis were performed in order to obtain information on significant atmospheric factors that affect gross α and gross β variability, which could be useful in identifying meteorological or atmospheric changes that could cause deviations in gross α and gross β activity depending on the seasons considered. Models obtained explain more than 60% of variability for global data, and also for winter and spring-autumn months. However, more research is needed to explain gross α and gross β variability in summer months, because the atmospheric factors considered in the MLR explain less than 35% of variability.