Technical Information

Even if the air quality of large canadian cities like Montreal or Québec City cannot be compared to that of Los Angeles or Mexico, some weather conditions of the summer can cause the formation of smog, a noxious mixture of air pollutants. Ground level ozone - which is totally different than the ozone layer found in the high atmosphere - is the main constituent of urban smog. It can cause health problems particularly to the elderly people, those with heart or lung disease and children. Ozone not only affects human health, it can decrease the productivity of some crops, may contribute to forest decline and can also damage synthetic materials, rubber and textiles.

INFO-SMOG is a smog forecasting and information program that aims to inform and advise the population when smog concentrations are likely to reach or have reached levels that are harmful to health and the environment. In addition, the program INFO-SMOG offers suggestions to the public on what they can do through small daily acts to help improve air quality, by using public transit, driving in a more environmentally-friendly way, and by limiting the use of solvents and volatile chemical products, for example.

The INFO-SMOG program cover all Southern Québec regions
(list of regions).
See map of regions.

Among others, the program consists of a daily air quality forecast in three categories. It is based solely on the ground-level ozone concentrations and fines particulate with diameter less then 2.5 micrometers. An INFO-SMOG warning is issued when the forecasted category is identified as POOR.

INFO-SMOG is a joint program of the Ministère de la Santé et des Services sociaux du Québec in collaboration with the Directions de la santé publique, the City of Montréal, the ministère du Développement durable, de l'Environnement et des Parcs and Environment Canada (EC).

The warnings issued by the INFO-SMOG program are enriched by the participation of the ministère des Transports du Québec. INFO-SMOG warnings will be broadcast on the panels overhanging highways in the greater Montreal region and also in Quebec city area. The warnings will be available on the Info-Travaux hotline. The population will be informed as quickly as possible when a smog warning is issued so appropriate action can be taken.

Additionnal information about the Info-Smog program and the smog in general can be found in the Info-Smog fact sheets hosted by the City of Montréal^*.

A process linked to the weather conditions

Smog formation and ground level ozone buildup occur most often during hot and sunny afternoons of the summer months. A combination of solar radiation, volatile organic compounds (VOC), mainly produced by evaporation of liquid fuels, solvents and organic chemicals, react with nitrogen oxides (NOx) produced by the combustion of gas, diesel and coal. The product of this reaction is ground level ozone. Ozone and its precursors can be transported over large distance in the atmosphere by the winds.

Smog formation is not only caused by long range transport and weather conditions, but also by the local conditions such as the size of cities, the density of population and traffic and the industrial activities. Smog not only exists near urban centers, but is carried over rural regions by the winds. Typically it is formed by mid-afternoon over urban centers and spread across rural regions late in the afternoon or in the evening. An ozone episode has a lifetime from a few hours to several days.

Issuing a smog warning

When air quality become poor, a warning is issued which asks the public to reduce their use of motor vehicles, solvents and volatile chemicals and to use public transit services. The warnings are issued 24 hours in advance. For more information on the criteria and when warnings are issued, please read the technical informations.