Chemical Characterization of Airborne Particulate Matter in New Zealand Cities

Abstract

This thesis "Chemical characterization of airborne particulates in New Zealand cities" focuses on the elemental composition of PM10 samples collected in three selected major New Zealand cities; Christchurch, Hamilton, and Auckland. The primary objective was to identify the sources of airborne PM10 and to apportion the sources. The secondary objective was; to identify the major sources of the brown hazes appear in Auckland during cold and calm winter months. PM10 samples were collected on quartz filters using a hi-volume sampler in each season from spring 1999 to spring 2001 in the three cities. The elemental composition was quantitatively determined for 14 elements using inductively coupled plasma/mass spectrometry (ICP/MS). In addition, the coarse and fine fractions of PM10 were collected on polycarbonate filters using a versatile air pollution sampler (VAPS) in Christchurch and Auckland during winter and summer. The elemental composition was determined with ion beam analysis (IBA) for 16 elements. Elemental carbon (EC) was determined with a light transmission/reflection method. Both the VAPS and hi-volume sampler was also used to collect PM10 on brown haze and normal days in Auckland. The elemental profiles of direct source samples; marine, soil, petrol, diesel, coal, and wood combustion emission were determined with ICP/MS and used to help identify the sources in the airborne particulates. Source identification was performed using principal component factor analysis (PCFA) using both the ICP/MS and IBA data sets. Some selected samples collected on brown haze days and some diesel, petrol, and domestic emission samples were inspected visually using scanning electron microscope (SEM) images to identify similar types of particulates on brown haze samples and the source samples. Meteorological parameters; wind speed and direction, ambient temperature, relative humidity, and rainfall data for the particulate sampling days were also considered for each location. The results showed that marine and crustal elements were dominant in the total elements mass detected in the particulates in all seasons in the three cities. However, according to the IBA data set EC dominated all elements in the winter. The total inorganic elemental concentration became minimal in colder months and maximal in warmer months. The source identification using PCFA for the ICP/MS data set revealed that the major sources of PM10 mass in the three cities were; sea spray, suspended soil/road dust, domestic emissions, diesel and petrol emissions. The IBA data set yielded six major sources; sea spray, suspended soil/road dust, fine soil, domestic emissions, diesel and petrol emissions. For source identification the elemental mass concentrations of the coarse and fine fractions collected using the VAPS and analyzed with IBA were more informative and advantageous over the elemental mass concentrations of PM10 collected using the hi-volume sampler and analyzed with ICP/MS. In all three cities a larger mass contribution from sea spray and a lower contribution from domestic emissions were found in spring/summer compared to autumn/winter. Christchurch in winter had similar contributions from both domestic and vehicle emissions, where as in Auckland even in winter the contribution from suspended soil, road dust, and vehicle emissions were larger than domestic emissions. Hamilton also showed a greater contribution from vehicle emissions compared to domestic emissions even in winter. Overall, vehicle emissions (a combination of both diesel and petrol emissions) appear to be more important in the three cities in both winter and summer. Significantly increased concentrations of elements such as S related to diesel emissions were found to be responsible for the build up of the brown hazes in Auckland under cold, calm, clear and humid conditions. Therefore from an elemental composition point of view a significantly increased contribution from diesel emissions due to lack of dispersion was the major source responsible for the build up of the brown hazes in Auckland.