Inter-comparison of online and offline methods for measuring ambient heavy and trace elements and water-soluble inorganic ions (NO<sub>3</sub><sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, NH<sub>4</sub><sup>+</sup>, and Cl<sup>−</sup>) in PM<sub>2.5</sub> over a heavily …

Abstract. Characterizing the chemical composition of ambient particulate matter (PM) provides valuable information on concentration secondary species and toxic metals assists in validation abatement techniques. The components PM can be measured by sampling filters analyzing them laboratory or using real-time measurements species. It is important for accuracy monitoring networks that from offline online methods are comparable biases known. concentrations water-soluble inorganic ions (NO3−, SO42−, NH4+, Cl−) PM2.5 24 h filter samples ion chromatography (IC) were compared with inorganics an aerosol mass spectrometer (AMS) a frequency 2 min. Also, heavy trace elements determined inductively coupled plasma spectroscopy (ICP-MS) half-hourly metal Xact 625i monitor. comparison was performed over two seasons (summer winter) at sites (Indian Institute Technology Delhi (IITD) Indian Tropical Meteorology, (IITMD)) which located National Capital Region (NCR), India, one most heavily polluted urban areas world. Collocated deployments instruments helped to quantify differences between evaluate possible reasons positive negative biases. slopes SO42− NH4+ closer 1:1 line during winter decreased summer both sites. higher due formation (NH4)2SO4. Filter-based NO3− lower than IITD IITMD volatile nature substrate. Offline-measured Cl− consistently AMS-derived Based their comparability characteristics, grouped into three categories. element data highly correlated (R2>0.8) Al, K, Ca, Ti, Zn, Mn, Fe, Ba, Pb correlation coefficient demonstrated precision these ICP-MS. Some showed elemental ICP-MS average 10 %–40 % depending season site. could distance inlets methods, interference measurements, strategy, variable blank filters, digestion protocol measurements.