Direct measurement of ozone production rates in Houston in 2009 and comparison with two estimation methods

Net ozone production rates, P(O-3), were measured directly using the Penn State Measurement of Ozone Production Sensor (MOPS) during the Study of Houston Atmospheric Radical Precursors (SHARP, 2009). Measured P(O-3) peaked in the late morning, with values between 15 ppbv h(-1) and 100 ppbv h(-1), although values of 4080 ppbv h(-1) were typical for higher ozone days. These measurements were compared against ozone production rates calculated using measurements of hydroperoxyl (HO2), hydroxyl (OH), and nitric oxide (NO) radicals, called calculated P(O-3). The same comparison was done using modeled radicals obtained from a box model with the RACM2 mechanism, called modeled P(O-3). Measured and calculated P(O-3) had similar peak values but the calculated P(O-3) tended to peak earlier in the morning when NO values were higher. Measured and modeled P(O-3) had a similar dependence on NO, but the modeled P(O-3) was only half the measured P(O-3). The modeled P(O-3) is less than the calculated P(O3()) because the modeled HO2 is less than the measured HO2. While statistical analyses are not conclusive regarding the comparison between MOPS measurements and the two estimation methods, the calculated P(O-3) with measured HO2 produces peak values similar to the measured P(O3()) when ozone is high. Although the MOPS is new and more testing is required to verify its observations, the measurements in the SHARP field campaign show the potential of this new technique for contributing to the understanding of ozone-producing chemistry and to the monitoring of ozone's response to future air quality regulatory actions.