GROUND-­‐LEVEL OZONE Ozone is a highly reactive chemical made of three oxygen atoms that is associated with two different parts of the atmosphere. In the upper atmosphere (the stratosphere), ozone is found in a thin layer (the ozone layer) and protects us from harmful ultraviolet rays from the sun. This is sometimes referred to as “good” ozone. In the lower atmosphere, the part of the atmosphere we breathe, ozone is one of the main components of smog and is harmful to our health and the environment. This “ground-­‐level ozone” can be thought of as “bad” ozone. Ground-­‐level ozone is formed in the air we breathe when nitrogen oxides and volatile organic compounds react in the air during hot sunny days. Since sunlight is very important in production of ground-­‐level ozone, the highest levels can be observed during the summer. The main source of nitrogen oxides in our airshed is vehicles. VOCs are emitted when solvents (e.g. paints, varnishes, personal care products) are used as well as being naturally released by vegetation. More information about the sources of air contaminants that form ground-­‐level ozone and the impacts ground-­‐level ozone has on our health and environment can be found in a Metro Vancouver fact sheet at http://www.metrovancouver.org/services/air/Documents/GLOFactsheet.pdf. A strategy to address peak and non-­‐peak ground-­‐level ozone has been developed jointly by Metro Vancouver, the Fraser Valley Regional District, BC Ministry of Environment, Environment Canada and Port Metro Vancouver. The background to the issue, current state of scientific knowledge and broad policy directions to advance policy and program development have been described in the Regional Ground-­‐Level Ozone Strategy for the Canadian Lower Fraser Valley Region. Ground-­‐level ozone levels are typically highest during the late afternoons of hot, sunny summer days. Measurements from the Lower Fraser Valley Air Quality Monitoring Network provide hour-­‐by-­‐hour information about the levels of ground-­‐level ozone in the region, which is reported on AirMap.ca. When concentrations become elevated to levels that are worse than the standards established for desirable air quality in our region, an air quality advisory may be issued to the public through the media, federal, provincial and local government websites and social media networks. Advisories issued by Metro Vancouver provide information about air quality levels, precautionary steps to limit exposure, and actions to reduce emissions such as minimizing the use of vehicles and gas mowers. Metro Vancouver issued a 48-­‐hour air quality advisory for eastern parts of Metro Vancouver and the Fraser Valley on Sunday July 13th after a period of hot temperatures and sunny skies caused air quality to deteriorate. Exceedances of the standards for ground-­‐level ozone were recorded for periods of between one and six hours. The highest concentrations recorded for a single hour were at Hope (85.9 ppb), Maple Ridge (84.1 ppb) and Agassiz (82.8 ppb). The advisory was lifted on the afternoon of Tuesday July 15th as temperatures cooled and levels of ground-­‐level ozone decreased.