[RESIDENTIAL BURNING, cont.]

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How does the BCAA determine whether or not to allow a "burn day"?

The burn day decision is determined by examining several factors.

• Mixing Level: The mixing level is the height to which air is thoroughly mixed and is usually transparent. Although, sometimes on cold winter mornings, the mixing level is visible as a thin line of clouds or mist. The mixing level is also sometimes called the "ceiling". If the mixing level is low, then pollutants can be concentrated. It is like being in a room with a cigarette, the bigger the room, the more air there is and the less the impact of the smoke. The reverse is also true, the smaller the room the more concentrated the smoke.
• Wind speeds: Related to the mixing level, the wind speeds help to determine how well the air below the mixing level is mixed. Gusty, light winds usually help raise the mixing level and keep pollutants diluted.
• Particulate levels: The BCAA monitors for particulate, which is small particles of smoke and dust, on a daily and hourly basis. Particulate levels are an indicator of how polluted the air is locally. On marginal days, the particulate level can be used to determine a burn day - if the levels are too high, allowing a burn day would only add to the problem.

By examining these factors, the BCAA tries to anticipate the effect of a burn day on the general pollution levels in the local area. A high mixing level with light winds is usually considered to be a good burn day. If the winds are forecast to be high, usually a burn day will not be allowed due to safety considerations. Often the snarly, cloudy, gusty days are considered to be good burn days. While the beautiful blue sky days seem to be good days to burn, the blue skies are usually due to low mixing levels, meaning that burning would cause more problems.

The information for determining a burn day is examined daily, with the decision being made and posted by 9 a.m.