Citizen science air quality monitoring is helping to give us a clearer picture of the localized pollution from residential wood burning.

Residential wood burning creates islands of neighborhood air pollution that are often not reflected in official monitoring numbers. In most communities, there are few (if any) official air pollution monitors, and they are rarely located in areas that are most affected by wood smoke pollution.

In the United States, for example, roughly two-thirds of counties have no official regulatory air monitoring devices.

As consumer-level monitoring devices have become more affordable and available, an increasing number of “citizen scientists” have been setting up their own home-based particulate sensors.

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…the true scale of [US air quality standards] nonattainment is difficult to quantify because there are few regulatory air quality monitors located in rural areas where wood burning is most prevalent.

NESCAUM. Assessment of EPA’s residential wood heater certification program.

PurpleAir sensors

PurpleAir sensors have become particularly popular in recent years. The readings from these Wi-Fi-connected laser particle counters are displayed in real time on an online map, making it easy to see how local air quality is affected by nearby sources of pollution, including wood burning.

Measuring what we’re actually breathing

Although PurpleAir sensors are not regulatory-grade instruments, they allow us to see trends in air quality between short distances.

When the major source of pollution is localized, as it is with residential wood burning, the PurpleAir map provides a more accurate idea of what we are actually breathing than measurements from a central monitor much further away.

Localized pollution from wood burning

For example, the screenshot below shows PurpleAir sensor readings for PM2.5 in Humboldt County, California, on a winter evening in January 2023. Wood stoves are common in this rural northwestern part of the state, and it can be seen how this affects air quality.

Some neighborhoods have good air quality, while others are polluted with wood smoke.

A screenshot from the PurpleAir map of Humboldt County, California, on the evening of January 19, 2023, showing air quality that is very good in some areas and very poor in others. The numbers are for PM2.5, ranging from zero in some places to 142 in a neighborhood in Fortuna.
PurpleAir sensor readings in rural Humboldt County, California show how air quality varies from neighborhood to neighborhood due to residential wood burning. (Click to enlarge.)

Another example is the PurpleAir map screenshot below showing part of British Columbia, also on a winter evening in January 2023.

Wood burning is common in this area, especially on Vancouver Island, and this is reflected by the areas of poor air quality. Urban Vancouver, on the mainland, is seen to have better air quality than in some smaller communities where there is more wood burning.

A screenshot of Vancouver Island and Vancouver, British Columbia, on the PurpleAir map taken on the evening of January 19, 2023. On Vancouver Island , several sensors are displayed with orange and red dots, indicating poor air quality. Most of the sensors in urban Vancouver are in the green and have lower readings.
This screenshot of PurpleAir sensor readings around Vancouver Island and Vancouver, British Columbia, on a winter evening shows how air quality can be affected by wood burning. (Click to enlarge.)

Accurate, low cost PM2.5 measurements

Australian researcher Dr. Dorothy Robinson developed calibration equations for PurpleAir monitors that provided estimates of wood smoke PM2.5 pollution “almost identical” to those from the official New South Wales government equipment they were compared with.

According to Dr. Robinson:

For most locations, calibrated PurpleAir PM2.5 are more accurate than those from a central monitor a few hundred meters away because spatial variation in wood smoke pollution is substantial and depends on local sources such as nearby wood heaters. More accurate exposure estimates allow improved estimates of both exposure–response relationships and health costs.

Issues with regulatory monitors

A special report from Reuters about regulatory air monitoring in the US found that the EPA’s air monitors “routinely miss pollution,” even during severe air quality incidents.

As part of the report, Reuters reviewed data from 10 citizen science air monitoring projects. “Those efforts often revealed pollution spikes and hot spots the EPA network never captured.”

Reuters found that official monitors were sometimes programmed to only record data sporadically, or were programmed to limit the amount of pollution they recorded.

For example:

A government monitor in Imperial County, California, operated by local and state regulators, recorded much lower readings of day-to-day air pollution in 2017 than were actually occurring because it had been programmed to max out at a lower level. The EPA acknowledged the issue to community organizations after the groups discovered higher readings with their own monitors.
Citizen science air quality monitoring references