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    Atmosphere - Air Quality
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State Indicators

Pollutant concentrations

When pollutants such as carbon monoxide, nitrogen dioxide, PM2.5, sulfur dioxide and ozone are present in high concentrations or for prolonged periods, these can affect the health of populations exposed to them (WB, 1998, 2002; Lacasaña-Navarro et al., 1999; ATSDR, 2002; Environment Canada, 2008). Health effects include eye, nose, throat and lung irritation and infections, exacerbation of asthma, pulmonary function impairment, inhibition of the blood’s ability to transport gases and increased morbidity in children under five years and vulnerable population (Semarnat-INE, 2003; WB, 2003).

To protect human health, governments in many countries around the world control the concentration of air pollutants through a variety of regulatory instruments. Mexico developed standards specific for each pollutant, which establish criteria for evaluating air quality by setting an upper concentration limit. In general, air-quality standards are set based on the results of toxicological and epidemiological studies that evaluate the relationship between exposure to a given pollutant and its health effects. In our country, mainly due to the lack of resources to conduct such studies, and to the problem’s severity in the early nineties, the Mexican air quality standards were based on the World Health Organization’s and the US Environmental  Protection Agency’s standards rather than on specific studies on the Mexican population (Semarnat, 2009; INE-Semarnat, 2007a).

To measure the concentration of pollutants, networks of air-quality monitoring stations have been installed. Currently, records of air pollutants are available for 53 metropolitan areas and towns across the country (Semarnat, 2009). Direct measurement of the concentration of these pollutants provides more accurate information for assessing air quality. In fact, standards that set forth allowable concentration limits are based on studies of health impacts as a function of the concentration and time of exposure to each pollutant. In this way, daily concentrations (24-h average for PM10 and SO2) and daily maximum concentrations (daily maximum values for CO and NO2 and daily maximum of the 8-h moving average for O3) are compared to the limit established in the corresponding air-quality standard (INE-Semarnat, 2007a).

To describe the air quality annual trend in air quality, this report shows annual mean concentrations. The indicator Annual mean concentrations for criteria pollutants and exceedance days describes the trends in air quality and provides a means to assess policy performance. The indicator is presented separately for six pollutants: carbon monoxide, nitrogen dioxide, particles smaller than 10 micrometres, sulfur dioxide, ozone and particles smaller than 2.5 micrometres. This shows the pollutants levels at which populations are exposed in metropolitan areas, as well as the level of compliance with the respective standard. This indicator is proposed by OECD, Environment Canada, the US-EPA and the initiative on Sustainable Development Indicators in Mexico (OECD, 2005; INEGI and Semarnap-INE, 2000; EPA 2003; Environment Canada, 2008).