Environmental Trends 2007

Air Quality

Communities in B.C. Achieving the Canada-Wide Standard for Ground-Level Ozone

Photo credit: Ministry of Transportation

Ground-level ozone is formed by chemical reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight. The component compounds for these reactions come from local emissions, such as burning fossil fuels, or are transported in the air from other regions.

Ozone concentrations vary by location and time of day. Hourly concentrations in urban areas are typically highest in the long days of summer when temperatures are highest and the sun is most intense.

Most communities achieved the Canada-wide Standard for ground-level ozone in 2004-2006. Only one (Hope, marked with a red dot) exceeded the CWS target.

Note: The CWS for ground-level ozone is 65 parts per billion (ppb) over an 8-hour averaging time. Jurisdictions compute the three-year average using the annual fourth-highest daily eight-hour average recorded each year. Source: B.C. Ministry of Environment

• Most communities in B.C. had levels below the CWS for ground level ozone (65 ppb). For the past 3 years, the CWS was exceeded at Hope, while readings at Chilliwack, Langley Central and Maple Ridge were at or near the CWS threshold.

• The highest annual mean concentrations of ground level ozone occur in the southern interior region, where summers are very warm and sunny. The lowest concentrations are measured in downtown Vancouver.

For detailed information, including graph data, see In-depth Report [pdf].

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