Air pollution exposure monitoring and estimation Part III. Development of new types of air quality indicators

The temporal pattern of exposure to a specific compound may affect health in several ways. Exposure to pollution can have short-term effects or long-term effects. For some compounds there is a threshold under which there is no presumed measurable effect, whereas for other compounds, there is no presumed threshold. For short-term effects, the exposure to a high concentration of a compound one day may either increase or decrease the response if values of the same compound become high again the next day. Adaptation to effects of short-term exposure to ozone, for example, is reported. Similarly, health response to sudden high peaks of concentration may also possibly differ in effect from those to peaks attained more gradually. For long-term effects of some compounds, the cumulative exposure may be more decisive in influencing health. This paper proposes and describes in detail several air quality indicators that reflect the time variability and the episodic nature of air pollution exposure, as an attempt to represent the temporal aspects of pollution exposure that may have important effects on health. Mean concentrations, 98th percentile and maximum values are the traditional indicators for estimating exposure. The temporal variability of particulate matter (PM10) and NO2, however, is here described by means of: (1) the rate of change of pollution as the difference between two consecutive hourly or daily values, and of (2) episodes, described in terms of number, duration and inter-episode period, maximum concentration in the episode, and integrated episode exposure.