Influence of ABL stability on the diurnal cycle of PM10 concentration: illustration of the potential of the new Veneto network of MW-radiometers and SODAR

Abstract

Stable boundary layer conditions are long known for causing increasing pollutant concentrations. The region of the Po Valley has a particularly unfortunate topographical conformation which favours low wind and strong inversion situations, a meteorological characteristic that leads to so-called episodic conditions, especially during the cold season. ARPAV-CMT has recently installed a network of boundary layer profilers consisting of four passive microwave radiometers and four SODAR, funded in the framework of the DOCUP 2000-2006 project (DOCumento Unico di Programmazione) and of the Project 'Air pollution in the city of Padua'. This network is briefly presented and an illustration is given as to its potential to analyse the PM10 (particulate matter with diameter lower than 10 μm) concentration evolution. An entire year of data as well as a high-concentration episode are analyzed. In particular, emphasis is given to the documentation of the diurnal cycle of PM10 in relation to the atmospheric stability. It was found that PM10 is strongly modulated by synoptic-scale forcing and exhibits a strong diurnal cycle, especially in synoptically undisturbed conditions, when PM10 can exhibit large variations in just a few hours. A conceptualization is proposed which accounts for the daily emission cycle for the interpretation of the diurnal cycle of PM10 concentrations in anticyclonic conditions. It pinpoints the fundamentally different accumulation and removal mechanisms of the particulate matter from the atmosphere in stable and unstable conditions, highlighting the importance of the atmospheric stability at the time of the evening emission peak during the cold season.