National air quality goals are extremely difficult to attain in the Los Angeles area,
despite decades of stringent air pollution control efforts and the substantial improvement
that has occurred because of those efforts. According to the 2007 AQMP, population
exposure to unhealthy levels of ozone had declined by roughly 35% since 1990, and even
the most heavily polluted areas of the region had seen almost a 50% decline in the number
of days they exceed the national ambient air quality standard for ozone.
3
Average
particulate levels have also been declining, though less sharply than ozone. Nevertheless,
the 2007 AQMP estimates that to attain the national ozone standard by 2024 as required by
the US Clean Air Act, it will be necessary to reduce regional nitrogen oxides (NO )
x
emissions by nearly 90% compared to 2006 levels. To attain the PM
2.
5
standard, it will be
necessary to reduce regional NO
x
emissions by 55%, and PM
2.5
emissions by 15%, also
compared to 2006 levels.
4
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