Introduction

According to the World Health Organisation, air pollution is the number one environmental threat to human health.¹ Despite Aotearoa New Zealand’s coastal landscape and relatively sparse population centres, it is not free from poor air quality. In fact, air pollution is responsible for more premature deaths in Aotearoa New Zealand than melanoma, diabetes, colon cancer, and road accidents combined.²

But it’s not just respiratory and cardiovascular issues that are of concern. Air pollution can impact cognitive function and lead to long term health effects,³ even from short term exposure.⁴ Despite such widespread knowledge, Aotearoa is currently far behind other developed nations in addressing its largest environmental contributor to premature death. 

For instance, exposure to ambient PM_2.5 - airborne particulate matter less than 2.5 µm in diameter - is associated with increased mortality and morbidity,⁵ leading to the regulation of ambient PM_2.5 in the USA since 1997,⁶ in the European Union since 2008,⁷ and in China since 2013.⁸ Yet, Aotearoa New Zealand currently does not regulate PM_2.5; instead, the country regulates PM₁₀ (<10 µm), which is less specific to anthropogenic sources and can include uncontrollable natural emissions, such as marine aerosol.⁹ Some countries have now gone a step further, looking to monitor ultrafine particulate matter (PM_0.1), such as through the East Asia Nanoparticle Monitoring Network (EA-Nanonet). Ultrafine particulate matter (< 0.1 µm) has the highest exposure risk, due to its deep penetration in the airways, increased retention in lungs, ability to translocate throughout the body, and potential to travel up olfactory nerves to the brain.¹⁰ 

Currently, Aotearoa New Zealand is not a leader in environmental health protections; in fact, it’s not even a follower.

Beyond the lungs

When air is inhaled into the lungs, gas exchange occurs at the alveoli, allowing oxygen to pass into the bloodstream. From here, the heart pumps oxygenated blood directly to the brain and throughout the body. If an air particle is small enough (e.g. PM_0.1), it can also translocate across alveolar cells and enter the bloodstream.¹⁰ Unfortunately for our brains (and bodies), the most significant sources of ultrafine particulate matter are anthropogenic activities (e.g. combustion),¹¹ meaning that the particles that can penetrate the furthest into our bodies are also the ones that are most likely to contain toxic compounds and carcinogens.

With this in mind, the breadth of cognitive health effects that have been linked to air pollution may not be a surprise. Populations that live near motorways are statistically more likely to develop dementia.¹² People who live in areas with increased air pollution have reduced measures of intelligence in studies that control for a wide range of covariates, such as socioeconomic factors.¹³ Exposure to air pollution is significantly associated with increased risks of schizophrenia, bipolar and personality disorders,¹⁴ depression,¹⁵ and possibly even autism.¹⁶

Of highest concern, however, are the impacts on the developing brain. Pregnant women exposed to increased air pollution have children with brain structure alterations and impaired inhibitory control, which could have significant long-term consequences.¹⁷ 

Even short-term air pollution may have severe impacts on foetal development. While exposing humans to air pollution is not an ethically viable experiment, unplanned primate studies have been used to model the potential outcomes of short-term exposure to air pollution. Pregnant rhesus macaque monkeys at the California National Primate Research Center exposed to nearby wildfire smoke had offspring with greater inflammation, blunted cortisol, more passive behaviour, and increased memory impairment compared to animals conceived after smoke had dissipated¹⁸ while infant rhesus macaques exposed to wildfire smoke had decreased immune system and lung function later in life.⁴ 

Enacting air quality regulations on ambient particulate matter can prevent negative health effects and premature death. Just four years after implementing PM_2.5 controls in China, it is estimated that over 42,000 premature deaths were prevented and more than 700,000 years of life saved.¹⁹ In the US, 239,000 early deaths are prevented annually thanks to air quality regulations, and when considering the costs of health care and days of work lost, the Clean Air Act has saved the US more than 2 trillion USD to date - a more than 30-to-1 return on investment.²⁰ In Aotearoa New Zealand, the estimated benefit-to-cost ratio of implementing stricter air quality regulations is 8.4,²¹ which does not account for cognitive benefits from reduced exposure to air pollution, and thus it is an underestimation of the potential benefits from regulation.

Air pollution in Aotearoa

Roughly 11% of annual deaths each year in Aotearoa are related to air pollution, with the largest contributions resulting from exposure to combustion sources: home heating and an ageing vehicle fleet.²² Combustion sources can contain a range of carcinogenic compounds, including benzo[a]pyrene and other polycyclic aromatic hydrocarbons, arsenic and heavy metals, dioxins, furans, and volatiles like benzene and formaldehyde.²³

While high density areas are usually the most impacted by poor air quality,²⁴ less populated areas of Aotearoa have some of the most prevalent air pollution issues. The airsheds with the largest number of days with PM₁₀ concentrations above current regulations are not located near major urban centres, instead located in Arrowtown (34 days of exceedance in 2020), Washdyke (35 days of exceedance in 2023), and Tokoroa (28 days of exceedance in 2021).²⁵ To be compliant with the National Environmental Standards for Air Quality, only one exceedance is allowed per year for each airshed (Fig. 1). While Washdyke is considered an industrial area, both Arrowtown and Tokoroa are inland and residential, making them prone to home heating emissions that can stagnate due to topography and associated temperature inversion layers. 

Fig. 1. Number of days exceeding the National Environmental Standards for Air Quality for PM₁₀ (50 µg m^-3) by airshed (provided by Stats NZ).

‍

Globally, exposure to air pollution is disproportionally tied to both socioeconomic status and race.^26,27 In Aotearoa New Zealand, it is estimated that health impacts from air pollution exposure are substantially higher in lower socioeconomic populations.²⁸ However, there remains uncertainty in the effects, partly due to the historical shortage of air pollution measurements with high spatial resolution. For instance, there wasn’t continuous air quality monitoring in the most densely populated regions of South Auckland until 2017,²⁹ and chemical characterisation of PM₁₀ at the site has not been reported. Yet, hair samples from across Auckland have found increased arsenic concentrations in populations located further from the central city, hypothesised to result from exposure to air pollution.³⁰

While the air pollution burden in Aotearoa is still under investigation, there are data available on the health effects commonly associated with air pollution exposure. Lung cancer incidence is 3-4 times higher in Māori compared to non-Māori populations.³¹ Overall, differences in mortality among communities cannot be explained by smoking rates alone, indicating other factors are contributing to the observed disparity.³² Roughly 25% of lung cancers occur in non-smokers,³³ and a recent landmark study examining lung tumours in “never smokers” from across the globe found that air pollution exposure correlated with both a decrease in telomere length and an increase in somatic mutations.³⁴ With growing evidence on the risks of air pollution, it is clear that further investigations in Aotearoa are urgently needed. 

Analytical techniques for particle analysis

Current air quality mortality estimates in Aotearoa are based on exposure to PM_2.5 and NO_2,²² despite air pollution containing thousands of different chemical species, each with its own toxicological risk profile. Thus, it is critical to conduct thorough chemical characterisation of air samples to understand the potential impacts to health. 

Chemical characterisation remains a challenge, however, as particulate matter is highly complex. Particles can be as small as tens of nanometres with a wide range of physicochemical properties, undergoing constant atmospheric transformation, such as through oxidation and radical initiated chemistry, heterogenous surface reactions, bulk particle phase chemistry, gas/particle partitioning, condensation/coagulation, and cloud processing (e.g. hydrolysis, oligomerisation). Knowledge of meteorological conditions and atmospheric chemistry processes are critical to interpreting air sampling data. 

During air sampling, particulate matter is typically size segregated by aerodynamic diameter using inertial impaction (e.g. cascade impactor) or centrifugal force (e.g. cyclone). From here, real time particle concentrations are usually determined via optical scattering or from attenuation of beta radiation (Beta Attenuation Monitor). Collection onto air filter membranes or impaction substrates can be used for off-line analysis, such as with chromatography, mass spectrometry, and spectroscopy-based techniques.

In Aotearoa, several techniques have been employed in the chemical analysis of off-line particulate matter samples. Elemental analysis has been completed using XRF to find that fireworks sold in Aotearoa contain Pb.³⁵ Pyrolysis GC/MS and µ-FTIR have been used to determine that the marine environment may be a source of local airborne microplastics.^36-38 LC/MS/MS has been used to quantify illicit drug concentrations in the air of Aotearoa’s largest city.³⁹ SEM/EDS and Raman microscopy have been used to quantify carcinogenic erionite fibres in Aotearoa.^40,41 The role of highly oxidised organics in relation to new particle formation has been investigated using Api-TOF-MS.⁴² ICP/MS has been used to identify vanadium from shipping emissions.⁴³ While these studies represents a non-exhaustive list, it is clear that many complementary methods are needed to characterise airborne particles. 

While not yet used in Aotearoa, the real time chemical analysis of single particles holds great promise for identification of air pollution sources. One powerful technique is the Aerosol Time-of-Flight Mass Spectrometer, which can produce particle size distribution data along with simultaneous chemical analysis of individual particles in both positive and negative ion modes.⁴⁴ This technique has been used to better identify sources of atmospheric particles⁴⁵ and uncover the atmospheric transport of bacterial and fungal species.⁴⁶

Overall, more innovative methods and studies are needed to understand pollution sources in Aotearoa so that mitigation strategies can be implemented to protect the health and well-being of New Zealanders.

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