Concentrations of particles in urbanareas of New Zealand pose a major air quality issue. Regional monitoring programmes have increased and become more extensive during the 1990s and show that PM10 concentrations breach the air quality guideline values in many urban areas. The impacts of these concentrations are significant (Fisher et al, 2002).
This technical report comprises a review of the health implications of PM10 concentrations in New Zealand and provides an overview of the existing knowledge on the health impacts of particle pollution.
Particles in the air can exist across a range of different sizes and chemical compositions. In New Zealand, historical monitoring of particles was based on measurements of total suspended particulate (TSP), which by definition includes all particles suspended in the air, although measurement methods have tended to capture those less than 20 microns in diameter. During the 1990s size selective inlets and monitoring methods were introduced to capture the PM10 size fraction, encompassing particles in the air less than 10 microns in diameter. An alternative methodology also used in some locations was smoke monitoring. However, this method was disregarded in most areas by the late 1990s as it is biased towards the measurement of elemental carbon. More recently, some monitoring of particles less than 2.5 microns (PM2.5) has been carried out in some locations.
The focus of much of the particle monitoring carried out in New Zealand has therefore been the PM10 size fraction. Similarly, the majority of the particle health effects studies both in New Zealand and overseas have also been based on measurements of PM10. The PM10 size fraction includes particles referred to as coarse and fine particles. These classifications were originally intended to separate particles based on the nature of their source, with coarse particles representing those formed through abrasive type mechanisms and fine particles those formed through combustion processes and chemical reactions. However, the terms are more commonly used now to represent particles in the size ranges less than 2.5 microns (fine) and between 2.5 and 10 microns (coarse). Fine-mode particles are formed through nucleation [Molecules of complementary substances combine to form a condensation nucleus.] and grow by coagulation [The combination of existing particles.] and the condensation of other gases on the particle nuclei. Coarse particles also include many natural sources such as pollens, spores and sea spray.
From a health perspective, the size of the particles is important as it affects their ability to penetrate into the lungs and cause adverse health effects. The larger particles (e.g. those greater than 10 microns) tend to settle in the nose and mouth and are unlikely to pose a health risk. Finer particles can penetrate further into the lung and alveoli and therefore may be associated with more severe health impacts. The mechanisms of formation (e.g. nucleation, coagulation and condensation for the finer fraction or the more abrasive formation systems of the coarser fraction) may also have implications for respiratory related health effects.