Air quality level in California US state: persistence and seasonality.

In this paper, the level of air quality in ten highly polluted cities in California US state is investigated by looking at persistence and seasonality properties of the time series based on fractional integration framework. Five pollutants, which are carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3) and fine and coarse particulate matters (PM2.5 and PM10), for ten selected cities, including Bakersfield, Los Angeles, and El Centro, are considered. The levels of CO, O3 and PM2.5 are above the exceedance limits for these ten cities, while the results of fractional integration show the possibility of mean reversion for PM2.5 whereas CO levels are still in non-mean reverting range. Levels of pollutants are found to be seasonal in all pollutant cases and across the cities. Since all pollutants pose serious concern to inhabitants of the cities, the California government should intensify more effort in making appropriate policy to reduce pollutant levels in the state. [ABSTRACT FROM AUTHOR]