Evaluation and application of a semi-continuous chemical characterization system for water soluble inorganic PM_2.5 and associated precursor gases

Abstract. Water soluble inorganic particles components (Cl⁻, SO₄²⁻, NO₃⁻, and NH₄⁺) and concentrations of their associated precursor gases (HCl, SO₂, HNO₃, NH₃) were semi-continuously measured using the Dionex Gas Particle Ion Chromatography (GPIC) system. Sampling was conducted adjacent to a high traffic street in downtown Toronto, Canada from June 2006 to March 2007. This study evaluated the precision and accuracy of field sampling measurements with the GPIC both relative to filter based measurements and other co-located semi-continuous instruments (R&P 8400N Nitrate Monitor, API Fluorescent SO₂ Gas Analyzer, and Aerodyne C-ToF-AMS). High temporal resolution PM_2.5 mass reconstruction is presented by combining GPIC measured inorganic species concentrations and Sunset Laboratory OCEC Analyzer determined organics concentrations. Field sampling results were also examined for seasonal and diurnal variations. HNO₃ and particulate nitrate exhibited diurnal variation and strong partitioning to the gas phase was observed during the summer. Ammonia and particulate ammonium also demonstrated seasonal differences in their diurnal profiles. However, particulate sulphate and SO₂ showed no diurnal variation regardless of season suggesting dominant transport from regional sources throughout the year.