Kitimat SO2 Alert Pilot Project

SO₂ is a colourless gas with a strong odour at higher concentrations. It is produced during the combustion of sulphur-containing fuels and industrial operations involving sulphur-containing materials. Major sources of SO₂ in BC include: the upstream oil and gas industry, metal smelting facilities, pulp and paper mills and marine vessels.

Short-term exposures to elevated SO₂ levels can cause the air passages in the lungs to constrict or tighten, leading to breathing difficulties and tightening in the chest. Those most sensitive to the effects of SO₂ include persons with chronic respiratory disease, especially persons with asthma. Symptoms may worsen during vigorous exercise or hard physical labour.

In general, persons with asthma may experience effects at much lower concentrations than the general public. In their Human Health Risk Assessment for Sulphur Dioxide, Health Canada identified a 10-min Reference Concentration (RfC) of 67 ppb – a level that is expected to be protective of human health, including sensitive groups such as those with asthma, when exposed continuously over a lifetime. This level is comparable to a 1-hour concentration of about 35 ppb based on SO₂ data evaluated for Kitimat. It is expected that 1-hour SO₂ levels of 35 ppb and lower will pose little or no additional health risk to even sensitive individuals.

The SO₂ alert system was started as a pilot project in Kitimat in response to local concerns about increasing SO₂ emissions and recommendations from the Environmental Appeal Board regarding the Rio Tinto permit amendment.

Beginning January 1, 2018, alerts have been generated whenever 1-hour SO­₂ concentrations reach 36 ppb or higher at any of three community monitoring sites in Kitimat (Whitesail, Riverlodge or Haisla Village). Alerts are posted at http://www.env.gov.bc.ca/epd/bcairquality/aqo/csv/alerts/so2.html. Members of the public can be directly e-mailed these alerts by signing up for the provincial Air Quality Subscription Service at https://aqss.nrs.gov.bc.ca/subscription.html (select "Kitimat"). 

Each alert message includes information on 1-hour SO₂ concentrations over the past hour and associated health guidance, focusing on advice for those most sensitive to SO₂ exposure. Table 1 summarizes the threshold values used and the updated health messages. 

The Air Quality Health Index (AQHI) is the most widely used tool in Canada to communicate with the public about air pollution. It is a scale from 1 to 10+ that reflects the level of health risk associated with air quality. It is based on the observed relationship between daily mortality and concentrations of three pollutants averaged over three hours: nitrogen dioxide (NO₂), ozone (O₃) and fine particulate matter (PM_2.5). This is referred to as the “three-pollutant AQHI”. For additional information on the three-pollutant AQHI, see https://www2.gov.bc.ca/gov/content/environment/air-land-water/air/air-quality/aqhi. 

The AQHI-Plus provides a way to include pollutants such as SO₂ and PM_2.5 that may cause short-term health impacts not otherwise captured by the AQHI. The ministry is testing the AQHI-Plus for PM_2.5 at all AQHI sites in the province, to better reflect the variable conditions during the wildfire season and other smoky periods of the year. The ministry is also testing the AQHI-Plus for SO₂ in Kitimat to alert the public to those levels of SO₂ that may affect the general population as well as persons with chronic respiratory conditions like asthma.

Under this approach, the AQHI-Plus for SO₂ is determined each hour by comparing the highest SO₂ concentrations among the three community monitoring sites in Kitimat to various pre-defined thresholds summarized in Table 2. The higher of the three-pollutant AQHI, the AQHI-Plus for PM_2.5 and the AQHI-Plus for SO₂ are reported as the “AQHI” value. This value is available at http://www.env.gov.bc.ca/epd/bcairquality/data/aqhi.html?id=AQHI-Kitimat.

When SO₂ levels warrant additional guidance beyond the standard AQHI messages, a special note is attached to the AQHI value. For example, a reported AQHI value of “2*” means that the health risk posed by air quality is low for the general population, but that due to elevated SO₂ concentrations, persons with chronic respiratory conditions such as asthma should take additional care if experiencing symptoms. An AQHI value of “7*” means that the AQHI has been adjusted upward to reflect an increased health risk for both sensitive populations and the general population due to elevated SO₂ concentrations.    

The special notes referred to in Table 4 are as follows: 

 *Elevated levels of sulphur dioxide have been reported. Persons with chronic respiratory conditions such as asthma should consider reducing or rescheduling strenuous outdoor activities if experiencing symptoms. No effects are expected for the general population. For more information, visit B.C.’s Ministry of Environment and Climate Change Strategy.

 ** Elevated levels of sulphur dioxide have been reported and the AQHI has been adjusted to reflect an increased health risk for both sensitive populations and the general population. Consider reducing or rescheduling strenuous outdoor activities if experiencing symptoms. For more information, visit B.C.’s Ministry of Environment and Climate Change Strategy.

Kitimat AQHI values are updated hourly and made available by the ministry at http://www.env.gov.bc.ca/epd/bcairquality/data/aqhi.html?id=AQHI-Kitimat. SO₂ is included in these calculations. Kitimat AQHI values are also reported by Environment and Climate Change Canada at https://weather.gc.ca/airquality/pages/provincial_summary/bc_e.html. 

The SO₂ alert system is based on the highest SO₂­ concentrations measured at the Kitimat Whitesail, Riverlodge and Haisla Village monitoring sites. The AQHI reflects a more holistic measure of air quality and what it means for an individual’s health. Under the Kitimat pilot, the publicly reported AQHI value is the higher of (1) the three-pollutant AQHI determined for the Whitesail station, (2) the AQHI-Plus based on 1-hour PM_2.5 levels at the Whitesail station, and (3) the AQHI-Plus based on the highest 1-hour SO₂ concentrations measured at the Kitimat Whitesail, Riverlodge and Haisla Village stations.

Some updates have been made to the SO₂ alert system, as summarized in Table 3, to ensure that its health messages are both consistent with those associated with the AQHI and appropriate based on the health evidence. These changes were reviewed by health experts at the BC Centre for Disease Control. The special notes associated with the AQHI-Plus for SO₂ are applied when additional guidance beyond the standard AQHI message is warranted to reflect elevated SO₂ concentrations.

As shown in Figure 1, each SO₂ alert describes:

• the time, location and 1-hour SO₂ concentration that was reached over the past hour,
• health advice appropriate for the SO₂ concentration, to help sensitive individuals, including persons with asthma, to adjust their activities to protect their health,
• the time that the next alert may be issued if concentrations remain elevated, and
• a web link to additional information on the website of the BC Ministry of Environment & Climate Change Strategy.

Figure 1. Example of SO₂ alert

SO₂ is monitored immediately north of the smelter, at the Haul Rd site, and at three community sites in Whitesail, Riverlodge and Kitamaat Village.

SO₂ levels in Kitimat are generally low, with the highest concentrations observed at the Haul Rd site located in an industrial area near the smelter. The Haul Rd site is considered an industrial fence line monitoring site, and not generally reflective of community air quality. In 2018, SO₂ concentrations at the community monitoring sites averaged below 1 ppb and 1-hour SO₂ concentrations did not exceed 36 ppb. Data from 2019 have yet to be fully validated, but based on preliminary information, the 1-hour SO₂ levels of 36 ppb was reached or exceeded on 7 different days at the three community monitoring sites to the end of September 2019. The highest value of 73 ppb was recorded at the Haisla Village monitoring site on August 19, 2019.   

On a seasonal basis, the highest SO₂ levels tend to occur in the spring through fall periods, when winds are mostly from the south. In general, SO₂ levels can change quickly with the weather conditions.

The SO₂ alert system is a public information tool only.  Emissions from the RT smelter are regulated under a permit issued by the Ministry of Environment & Climate Change Strategy. Criteria for triggering a reduction in emissions and/or other mitigation are described in the Environmental Effects Monitoring (EEM) program plan that is a requirement of the permit amendment. 

Canadian Ambient Air Quality Standards (CAAQS) for SO₂ were endorsed by the Canadian Council of Ministers of the Environment in 2016. These include standards based on one-hour and annually-averaged data for 2020 and 2025 (see Table 4). The 1-hour CAAQS is primarily intended to protect human health, whereas the annual CAAQS is intended to protect ecosystems.

When SO₂ concentrations are elevated, consider reducing or rescheduling activities outdoors, remaining indoors, and reducing indoor sources of SO₂ including tobacco smoke, wooden matches, and unvented gas stoves. Persons with asthma should follow a management plan developed with their health care provider. If you are having trouble in breathing, chest pain or discomfort, or a severe cough, contact your health care provider, walk-in clinic, or emergency department. See HealthLinkBC for summary health recommendations and Heath Canada’s Human Health Risk Assessment for Sulphur Dioxide for more detailed information.

The AQHI-Plus for SO₂ will be piloted in Kitimat until enough data is available for its conclusive evaluation. The project involves an ongoing assessment for further application.

During this period, the Ministry will continue to operate the SO₂ alert system. A decision on next steps will follow the project review.