New Zealand’s unhealthy home-heating in the age of COVID-19: Part 3: What impact does home-heating have on air quality and health?

As we start heading into winter a source of airborne particles emerges and rapidly comes to dominate PM levels across much of the country. Until relatively recently, wood was the natural choice for a home heating fuel in a country with plenty of trees. But it is also a relatively inefficient fuel. It is very hard to burn it completely, especially when it’s in the form of logs. The result is lots and lots of by-products, many of which are toxic or carcinogenic, and which collectively form the thick, pungent smoke that rises from thousands of New Zealand homes, mainly starting in April.

In Auckland, less than a quarter of homes still use wood, yet there are enough for average levels of PM10 rise by a third between April and June every year. In central North Island, and most of South Island wood-heating is more prevalent. Where it is colder, and traffic levels lower, the effect is most dramatic. In Timaru, for instance, woodsmoke can cause PM₁₀ to double between April and June. In many smaller inland South Island towns winter PM10 is pretty much all woodsmoke.

Nearly all of our breeches of the National Environmental Standards for air quality occur during cold and calm days in winter. On these days afternoon air quality is often excellent. But from about 4pm onwards levels of PM shoot up in a few hours and often stay high through until the early hours of the morning. This PM is almost entirely composed of woodsmoke (or in some locations coal smoke) from home heating. What is remarkable is how few homes it takes to create air pollution many times worse than in big cities like Auckland. In 2019 New Zealand’s two most polluted towns (in terms of the most breeches of the Standard) were Arrowtown and Milton, two Otago towns with populations a little over 2,000.

Calculations, which are based on overseas studies on larger populations, suggest that the impact on our health is considerable. Of the approximately 650 deaths and same number of hospitalisations a year attributed to PM exposure, around 70% is related specifically to biomass smoke in the North Island, and over 80 % in the South Island.

It is well worth understanding that, much like COVID-19, people are not equally vulnerable and the impact on health is not evenly borne across the population. Many people can be exposed to smoke over many years and never notice any ill-effects. But many others have serious vulnerabilities for a wide range of reasons. Children of all ages, but especially infants are vulnerable, as are foetuses. Anyone with pre-existing respiratory and cardiovascular health problems may also find their conditions worsened by air pollution.

As well as the more dramatic impacts, it is likely that a great many more people are impacted in more subtle ways. Anecdotally we hear about people who will forego or curtail activities that contribute to their wellbeing because of smoke in the air – social events, sport and exercise. Many asthmatics will find breathing uncomfortable. Clothes, curtains, bedding and whole buildings can be soiled. The smoke can also form part of a town’s public image causing a stigma that discourages inward investment. These subtle impacts are not captured in any official datasets, making them seem invisible. Yet high numbers of complaints to regional councils, which sometimes lead to court cases, are considerable and indicate that although many people are relatively oblivious to the effects that smoke causes, it blights the lives of many others.

Coming soon...Has COVID-19 and the lockdown changed the risk from woodsmoke?