Composition and Sources of Aerosol in the Wellington Region of New Zealand

Abstract

In 1998, Wellington Regional Council embarked on a series of short-term air quality screening surveys at various locations in the Wellington Region in order to provide an indication of ambient air quality and whether there were any air pollution issues to be addressed. It was found that air quality at some locations, predominantly during winter months, was degraded and that concentrations of fine particles exceeded national and international guidelines for the protection of human health. A broad scale emissions inventory for the Wellington Region conducted at the same time indicated that motor vehicle exhaust emissions were responsible for the majority of criteria air pollutant (CO, NOx, SO2, VOCs) discharges to atmosphere. Solid fuel fires for domestic heating were found to dominate the emissions profile for fine particles (PM10) during the winter. At the same time as setting up an ambient air quality monitoring network for the Wellington Region, the Council joined an international source apportionment programme in Australasia led by GNS Science under the auspices of the Regional Cooperative Agreement (RCA) and the International Atomic Energy Agency (IAEA). The project involved collecting samples of particles in two size fractions (PM2.5 and PM10-2.5) and determining the elemental composition from Na to Pb of those particles. Analysis of the resultant elemental concentrations allowed the relative contributions of different sources to air pollution episodes to be apportioned. This work presents the results of particle composition and source apportionment studies carried out at Baring Head, Upper Hutt, Seaview industrial area and Masterton. Source elemental profiles were also determined for motor vehicles emissions (Mt Victoria Tunnel study) and from domestic solid-fuel fire emissions to assist in source identification. The major findings of the study are that domestic solid fuel fire sources are responsible for 80 – 90 % of ambient particle concentrations during air pollution episodes (all in winter months) and that the seasonal variation in PM10 is dominated by the fine fraction (PM2.5). Marine derived aerosol and crustal matter sources provide an ubiquitous low-level ambient particulate matter background. They are the predominant sources for the PM10-2.5 size fraction and for both fine and coarse size fractions during summer months. Motor vehicle sources were found to be important contributors in more urbanized locations, both to the coarse fraction (re-suspended road dust) and the fine fraction (combustion exhaust emissions). Scanning electron microscopy was used to provide information on individual particle size, composition and morphology associated with different sources. A library of these different particle types has been compiled.