In 2009, the city of Los Bernardinos ranked worst nationwide with 148 days of unhealthy air after a report was published by the Environmental Protection Agency. In early 2010, a series of pollution control measures were enacted by local government. Still, that year the city recorded smog alerts on 153 days and 160 days the following year. In 2012, however, the number of smog alerts in Los Bernardinos dropped to 118. Air pollutants from cars, buses and trucks, particularly ground-level ozone and particulate matter, can worsen respiratory diseases and trigger asthma attacks. These pollutants have been measured by gas spectrography from 2009-2012.
Which of the following statements, assuming that each is true, would be LEAST helpful in explaining the air pollution levels in Los Bernardinos between 2009 and 2012?