PurpleAir monitor FAQ

What is a PurpleAir monitor?

PurpleAir Monitors are installed in various locations throughout the CVRD. As of September 2017, 11 air sensors were installed. These monitors are low-cost air quality monitors that measure microscopic particles in air, including PM2.5 . The PurpleAir monitors generate real-time air quality data which is sent to PurpleAir via the internet for display on a map on the PurpleAir website – found here.

This network was developed in response to the community concerns about air quality and the desire for more affordable means of neighbourhood-level data. The network was designed with significant input and decision-making from the Cowichan Airshed Protection Roundtable.

Where are the PurpleAir monitors?

The PurpleAir sensor network can be found here

What is the difference between PurpleAir monitors and the air quality monitors used by the BC Ministry of Environment & Climate Change Strategy?

Air monitors operated by the Ministry of Environment & Climate Change Strategy (MoE) are used to measure air quality to see if pollution levels meet federal air quality standards. There are currently four government monitors in the CVRD used for regulation.

Our network measures air quality at additional locations throughout the region. However, our monitors are different from government monitors and cannot be used to assess if air pollution levels are within legal limits. But they provide other important information. For example, community members can find out current air quality at a specific location and can take the necessary actions to protect health. Air quality data from PurpleAir monitors can also be used to understand general trends in air quality and in localized areas where the provincial monitors do not reach.


BC MoE Monitors

Purple Air monitors




Readings relative to actual levels

Close to actual



Very High


Meets requirements for regulatory monitoring






Distribution across the CVRD



1Accuracy refers to how close the measured concentration is to the actual conditions

2Precision refers to how close repeated measurements are to each other under unchanged conditions

How can the PurpleAir Monitor information be used?

The lower cost of PurpleAir monitors means we can more affordably install several of them in our neighbourhoods. There are differences between the uses of information provided by the BC MoE and PurpleAir monitors:

BC MoE Monitors

PurpleAir monitors

·      Comparing PM2.5  levels to provincial or federal air quality objectives

·      Identifying air quality patterns over various timescales (hourly to annual)

·      Identifying possible sources

·      Understanding the distribution of PM2.5 in a community

·      Identifying air quality patterns over shorter timescales (hourly to monthly)

·      Identifying possible sources

What is an Air Quality Index (AQI)?

The AQI is used to communicate how clean or polluted the air is. Different jurisdictions have developed their own air quality guides based on their own objectives, standards, and policies. The AQI used by PurpleAir is based on the US Environmental Protection Agency’s AQI.

Limitation of Purple Air’s AQI

The AQI displayed on the PurpleAir map does not correctly apply the US EPA AQI. The US EPA AQI for PM2.5 is based on the 24-hour average PM2.5 concentration, which is the average of all PM2.5 concentrations measured at a station over the previous 24-hours. In contrast, the AQI presented on the PurpleAir map is based on the current or real-time PM2.5 concentration. While the AQI presented on the map is a useful snap-shot of the current air quality conditions at the location of a PurpleAir monitor, it is not necessarily a good indicator of potential health risks. There is currently not enough information on what exposure to PM2.5 for very short periods (such as 20 seconds or even 10 minutes) could mean for our health.

What are the numbers displayed on the online PurpleAir map?

Data from PurpleAir monitors are displayed on an on-line map maintained by PurpleAir. The map can be accessed through the PurpleAir website. The number displayed in the icon is an Air Quality Index (AQI) that is calculated from the measured PM2.5  level. The colour of the circle represents the AQI category. However, these colours are not to be mistaken for Environment Canada’s Air Quality Health Index (AQHI), shown below.

What does it mean if a monitor is offline?

An offline monitor (colored grey) means that data from the monitor are not being reported to the website. This can happen for several reasons: The monitor may have become disconnected from the internet and needs to be reconnected; power outage; or, the monitor may require routine maintenance or may need to be replaced. CVRD staff get automatic notifications if a monitor stops reporting data or if the data look unusual. They then will take steps to make sure monitors are working correctly and reporting data to the PurpleAir website.


What is PM2.5?

Size:             PM2.5 refers to microscopic particles in air with a diameter (or width) of 2.5 micrometers or smaller. This is more than ten times smaller than the width of a human hair.

Sources:     PM2.5 can come from both natural and human caused sources. The two main human caused sources are the burning of wood and fossil fuels.

Impacts:     PM2.5 particles are small enough to penetrate deep into the lungs where they have the potential to cause respiratory and cardiac problems.

How does short-term exposure to particulate matter affect health?

Short-term exposure to particulate matter (PM) pollution can most strongly affect people with heart or lung diseases, people with other serious health issues, and pregnant women.

If you have a lung disease, such as asthma: Being exposed to PM pollution for short periods of time, such as hours or a few days, can make lung disease worse, cause asthma attacks, cause bronchitis, and make it easier to get respiratory infections. If PM levels are high:

  • You may not be able to breathe as deeply or strongly as normal
  • You may cough more, have chest pain, wheeze, feel like you can’t catch your breath, and be tired more than usual
  • Follow your asthma management plan if you have asthma

If you have heart disease: Being exposed to PM pollution for short periods of time, such as hours or a few days, can cause irregular heartbeat or heart attacks. If PM levels are high:

  • Serious problems, such as heart attack, can happen in a short period of time without any warning signs. If you think you are having a heart attack, call 9-1-1 immediately.
  • Symptoms like chest pain or tightness, fast heartbeat, feeling out of breath, and feeling tired more than usual may be signs of a serious problem. If you have any of these symptoms, follow your doctor’s advice and contact your doctor if they last longer than usual or get worse.

If you are pregnant: Short-term exposure to PM among pregnant women has been associated with giving birth too early and having babies that are too small. Pregnant women should try to reduce exposure to high levels of PM as much as possible.

Short term exposure to PM has also been linked with premature death, usually in people who already have a serious health problem like lung or heart disease. Healthy children and adults usually do not have serious problems from short-term exposure to PM. They may have minor problems, like a scratchy throat or scratchy eyes when PM levels are elevated.

How does long-term exposure to particulate matter affect health?

Long-term particulate matter (PM) exposure has been associated with heart and lung problems. Being exposed to PM pollution for more than a year is linked to problems like:

  • Breathing problems
  • Reduced lung function
  • Chronic bronchitis
  • Heart disease
  • Lung cancer

These problems may lead to more hospital stays, more emergency department visits, and even premature death. Sensitive people such as older adults, people with diseases like asthma or congestive heart disease, and children are more likely to be affected by contact with PM.

How can I reduce my exposure to particulate matter?

Be aware of the air quality around you and take appropriate action when levels of pollution are unhealthy. We recommend that you check the regional air quality and sign up for alerts from the government regulatory air monitoring network, as this will provide different information.

When particulate matter (PM) levels in the air are very high, everyone can reduce their exposure by spending less time outdoors and reducing physical activity levels (e.g. walking instead of running) You can also plan your daily activities to reduce exposure to PM. For example, exercise away from roads, highways, or other sources of PM, especially if you are in a group at high risk of having health problems from PM pollution.

Where does particulate matter come from?

Particulate matter (PM) comes from a variety of sources:

  • Motor vehicles
  • Dust from construction, landfills, and agriculture
  • Wildfires and brush/waste burning
  • Industrial sources
  • Wood burning stoves and fireplaces

In the CVRD, PM2.5 sources of concern include vehicle traffic along the Trans-Canada Highway corridor, dust from unpaved roads, and smoke from woodstove and open burning from residential, commercial, and agricultural operators. Specifically, home heating with wood (23%) and open burning (53%) contribute to 76% of the CVRD’s total PM2.5 emission levels.