OH and HO2 Measurements in Houston TX, during SHARP 2009

OH and HO2 radicals have been measured during the 2009 SHARP field campaign in Houston, TX using the Ground-based Tropospheric Oxide sensor (GTHOS). OH measurements were performed by two methods: wavelength modulation and chemical modulation. In the wavelength modulation method (“by line”) the OH signal was detected by Laser Induced Fluorescence as the online-offline signal difference with wavelengths near 308 nm. The chemical modulation method involved the quantification of OH from the amount of signal removed upon addition of C3F6 (“C3F6 method”). Significant differences were observed between the two methods. The “by line” method showed hourly peak OH radical concentrations of about 0.8 pptv, similar to the OH values found in the TEXASQ2000 field campaign, while the “C3F6 method” shows maximum hourly values for the OH concentration in the range of 0.5-0.6 pptv. The HO2 radical concentrations reached maximum concentrations of up to 60 pptv, similar to the TEXASQ2000 field campaign. In this presentation, we will discuss the implications of these measurements and the comparison with other studies.