The United States Congress, in the year 1960, voted to draft an act that later evolved into existence as the Clean Air Act in 1970 (US Environmental Protection Agency, 2012), owing to the escalation of the dense smog in the US metropolitan cities. Thus, Section 109 of the Clean Air act compelled the authorities to revise the emission standards for on- and off-road motor vehicles in the same year. The framework and the protocol circumscribing the carbon monoxide emission were introduced in 1971, with the collaborative support from the United States National Ambient Air Quality Standard (NAAQS). Owing to the metamorphosis of carbon monoxide pollution, the state decided to introduce a phrase called ‘Time-weight average exposure,’ which had a limiting value of 9 ppm for 8 hours and 35 ppm for 1 hour in an outdoor environment, calculated cumulatively for a year. The primary motivation for establishing the standard was to enhance public health and to provide a measure to protect the public welfare. The content and the objectives were successively reviews in 1985, which yielded the (US Environmental Protection Agency to maintain the primary standard without revision but revoked the secondary standard due to lack of evidence demonstrating a direct effect of ambient CO levels on public welfare. However, the primary criteria for the emission levels have never undergone any modifications since then, making the benchmarked points to remain functioning even today. The NAAQS was developed into two stages, where the first stage was to assess the figures via statistics and probability. In contrast, the second phase consisted of various primary and secondary surveys to bolster the theoretical numbers. A pivotal basis for the study was based on the correlation between the post-exposure rise in the carboxyhemoglobin and the post exospores time reduction of the coronary artery diseases sensitive toward carbon monoxide positioning.
Recently, the Environmental Protection Agency is working closely with the state local and tribal agencies to amend the standards set in 1971. The organizations are overviewing various aspects of the pollution ranging from air quality and using algorithms to predict future trends. In this context, the World Health Organization has also framed a guideline for the time-weighted carbon monoxide exposure to help prevent various physiological complexities originating from carbon monoxide emission. The WHO recommends limiting exposure to 9 ppm CO for 8 hours, 26 ppm CO for 1 hour, 52 ppm CO for 30 minutes, and 87 ppm CO for 15 minutes, assuming that the carboxyhemoglobin level must have an elevated bracket of 2.5% when a healthy adult human is exposed to moderate exposure. Along with the assertion, the US government has also laid down specific permissible standards for the indoor exposure of the carbon monoxide.
One of the examples may be cited from the Occupational Safety and Health Administration (OSHA) who recommends the carbon dioxide limiting exposure to be 50 ppm for 8 hours with a threshold concentration of 200 ppm. The figures were adopted from the Underwriters Laboratories, who had initiated the process of establishing an ‘indoor carbon monoxide level’ cutoff value in 1992. The data were based on the assumption that beyond the 10% exposure of carbon dioxide in a closed environment, a patient with cardiovascular disease experienced a dramatic rise in various supplementary risks.
With the advent of climate change, the US Environmental Protection Agency is once again planning to amend the cutoff values for the carbon monoxide emission.
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