For location c (low routine emissions), despite the fact that routine emissions total approximately 10 kg h -1 km -2 , the enhancement ratio, ER, for a 1000 kg/hr event averages only 1.42 when the simulation is done at a 4 km resolution, indicating a 1000 kg event only increases local column concentrations at location c by 42%, on average. As shown in Figure , there are time periods when ER is relatively large, reaching a maximum value of 3.82. These periods of high ER are relatively infrequent, however; as shown in Table . ER only exceeds 2 in 6.9% of the simulation hours and exceeds 3 in 0.7% of the simulation hours. If the time period for analysis is restricted to daylight hours, the time periods of high ER are lower; in the 1300-1400 hour time period, the ER only exceeds 2 in 2.8% of all 1300-1400 simulation hours, as compared to 6.9% for all hours.