Canadian National Air Pollution Surveillance (NAPS) PM2.5 speciation program: Methodology and PM2.5 chemical composition for the years 2003–2008

The Canadian National Air Pollution Surveillance (NAPS) network, monitoring criteria gases (CO, O3, NOx, and SO2), PM2.5, PM10, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs) and particle chemical mass and composition, has been in operation for over 40 years. Since 1984 both fine (<2.5 μm – PM2.5) and coarse (2.5–10 μm – PM10–2.5) particle mass measurements have been made at NAPS network sites using dichotomous samplers. In January 2003, the NAPS PM2.5 speciation program was initiated with the purpose of measuring all major components of PM2.5, including ammonium nitrate, ammonium sulphate, metals, and organic and elemental carbon. The present paper describes the improved sampling (e.g. Teflon/Nylon filter packs for nitrate loss, and an active blank for each and every sample in the determination of positive organic carbon artifacts), and analytical methods used in the Canadian NAPS PM2.5 speciation program. A detailed dataset was then analyzed for seasonal and geographical variations in the major components of 24-h time integrated PM2.5 samples collected at eight urban and three rural measurement sites across Canada (2003–2008). Chemical mass reconstruction was used for assessment of the adequacy of selected sampling and chemical parameters as well as for the determination of the relative contributions of different compound classes to PM2.5 mass. The highest frequency of PM2.5 episodes exceeding 30 μg m−3 were observed in Ontario and southern Quebec. In general, the most important contributions to PM2.5 mass were secondary aerosol sulphate and nitrate (38–63% for western sites and 3–44% for eastern sites), depending on the season. Organic matter (OM) was found to be the second most important component (21–45%), while particle-bound water (PBW) accounted for 6–12% of the PM2.5 mass. Golden B.C. was an exception, exhibiting high levels of OM (60–70%) and low levels of PBW (∼3%).

Research highlights
► The Canadian NAPS PM2.5 Speciation program provides detailed PM2.5 composition data.
► Major components of PM2.5 were secondary sulphate, nitrate, and organic matter.
► Teflon/Nylon filter packs controlled for nitrate loss (summer ∼90%; winter ∼20%).
► Active blanks for each sample accounted for positive organic carbon artefacts (34–61%).