Method development and monitoring of trace and major species in particulate matter by inductively coupled plasma--dynamic reaction cell-mass spectrometry

Abstract

In this thesis, new methods are developed to analyse both trace and major species in particulate matter (PM) by a new technology: inductively coupled plasma – dynamic reaction cell- mass spectrometry (ICP-DRC-MS). General background about atmospheric pollution is introduced. Of the major pollutants emitted, PM has attracted attention due to its adverse health effects. The properties of PM are discussed and previous studies and results for PM concentrations using different analytical methods are presented. Five year (1995-1999) datasets of chemical compositions in PM10 from three monitoring sites of the Hong Kong Environmental Protection Department (HK EPD) are presented. Carbon-containing compounds and SO4 2- contribute most of the aerosol mass. Concentrations of most chemical constituents show a high degree of seasonality, with high concentrations in winter but low ones in summer, resulting from the combined effects of summer monsoon scavenging and the influx of the continental airmass of the winter monsoon. High correlations exist within crustal (Al, Fe, Ca2+, Mn) components, as well as within sea-salt (Na+, Cl- and Mg2+) components. Non-seasalt- (nss-)SO4 2- and NH4 + ion contributions to the PM10 mass are similar at all sites and are greatest in the winter months. Chloride depletion is observed for many aerosol samples, but the bromide concentration approaches the seawater average. The concentrations of chemical components in PM10 from this study are compared with results from other countries including USA. In general, the Asian countries experience more elevated concentrations. The development of an analytical method for the determination of platinum group metals (PGMs: Pt, Pd and Rh) in environmental samples has been of concern in recent years because vehicles fitted with catalytic converters are spreading this element throughout the environment. A method for analysing low concentrations of Pt in roadside dust by inductively coupled plasma - dynamic reaction cell - mass spectrometry (ICP-DRC-MS), employing NH3 reaction gas, is presented. The use of DRC technology permits the removal of the interfering species HfO+ in Pt determination. The analysis of dust, collected by a modified vacuum cleaner at the roadside, employed digestion in a microwave oven by aqua regia, with subsequent filtration. The detection limit obtained was in the region of 8-10 ng g-1 for different Pt isotopes. Our results show that the conventional ICP-MS empirical corrections for such isobaric interferences of Pt may be inaccurate. Results are presented for Pt concentrations in road dust at various sampling locations in Hong Kong and these are highly correlated with vehicle traffic densities, but are not significantly correlated with the vehicle tracer species (Ce and Zr). The mean concentration of Pt in <63 μm road dust in Hong Kong was 205±100 ng g-1. The difficulties of analyzing other PGMs, Rh and Pd, are discussed. Pt in airborne PM was monitored for one month at two sampling sites, City University (CityU, residential) and Mong Kok (MK, high traffic density). Samples were taken with high volume air samplers (HVS) for 48 hours and analyzed by ICP-DRC-MS with the same optimization as the road dust samples. The 194Pt concentration was higher at MK, and was in the range from 5.9 to 37.4 pg m-3 at both sites, with an average value of 16.9 pg m-3. Concentrations of gaseous SO2, NOx, NO2, NO, CO and wind speed at MK averaged over the sampling period have been correlated with the measured Pt concentrations. By contrast with Pt in road dust samples, airborne Pt is significantly correlated with vehicle tracer species. A novel method of using DRC technology has been developed for the measurement of sulphur (S) in PM10, employing oxygen reaction gas. Samples were collected with a HVS at the roof of CityU for one month on a daily basis. By applying DRC technology, sulphur reacts with oxygen to form sulphur monoxide (SO). Soluble and total S were extracted by: water and acid digestion. Inductively coupled plasma atomic emission spectrometry (ICP – AES) and ion chromatography (IC) were used for the determination of total and soluble S. Concentrations in PM10 ranged from 3.3 – 7.0 μg m-3 and 3.4 – 7.6 μg m-3 for soluble and total S, respectively. Both species were highly correlated with the corresponding Ca and Mn contents. Soluble S (on average, 5.2 μg m-3) was slightly less than the total S (5.5 μg m-3). Soluble S (4.9 μg m-3, on average) determined as SO4 2- using IC was similar to the soluble fraction of S determined by ICP-DRC-MS.