Air pollution according to the south coast air quality management district, the level of nitrogen dioxide, a brown gas that impairs breathing, present in the atmosphere on a certain may day in downtown los angeles is approximated by
![2163_5797cc5d-e654-4a70-9bfc-63fcdc634971.png](https://secure.tutorsglobe.com/CMSImages/2163_5797cc5d-e654-4a70-9bfc-63fcdc634971.png)
Where a(t) is measured in pollutant standard index (psi) and t is measured in hours, with t = 0 corresponding to 7 a.m. At what time of day is the air pollution increasing, and at what time is it decreasing?