Time-resolved measurement of the ionic fraction of atmospheric fine particulate matter.

From the health stand-point, atmospheric particulate matter (PM) is regulated through PM(10) and PM(2.5) conventions by the Directive 2008/50/EC. The Directive points out the negative impact on human health due to PM(2.5) and recognizes that no threshold has been identified for such pollutant at which no risk is foreseen for the population. Then, the goal is to pursue a general reduction of PM(2.5). Traditionally, the analytical techniques used to monitor the PM water-soluble inorganic ionic fraction involve filter-based procedures to collect, process, and analyze samples. Data obtained, while accurate, lack temporal resolution. Time resolution is required on the time-scale of the evolution of the planetary boundary layer to understand the processes that govern transport and transformation of atmospheric aerosol. In this paper, we investigated PM(2.5) nitrite, nitrate, sulfate, chloride, sodium, ammonium, calcium, and magnesium ions using a URG 9000-D aerosol ion monitor with 1-h time-resolution and detection limit of 0.1 microg/m(3). The gas phase is separated from the aerosol phase with a liquid diffusion parallel-plate denuder. Daily trends of the pollutants measured in downtown Rome are discussed and interpreted with reference to atmospheric conditions.