Field measurements and analysis of reactive tropospheric species using the FAGE technique

Measurements of OH and HO2 using the Fluorescence Assay by Gas Expansion (FAGE) technique were made during a series of nighttime and daytime flights over the UK in summer 2010 and winter 2011. OH was not detected above the instrument’s limit of detection during any of the nighttime flights or during the winter daytime flights, placing upper limits on [OH] of 1.8 × 106 molecule cm−3 and 6.4 × 105 molecule cm−3
for the summer and winter flights, respectively. HO2 reached a maximum concentration of 3.17 × 108 molecule cm−3 (13.6 pptv) during a nighttime flight on 20th July 2010.
Analysis of the rates of reaction of O3 and NO3 with the alkenes measured indicates that the summer nighttime troposphere can be as important for the processing of VOCs as the winter daytime troposphere. Analysis of the instantaneous rate of production of HO2 from the reactions of O3 and NO3 with alkenes has shown that, on average, reactions of NO3 dominated nighttime production of HO2 during summer, and reactions of O3 dominated nighttime HO2 production during winter.
Measurements of IO were made by laser-induced fluorescence (LIF) during a cruise between Singapore and Manila in November 2011. The mean IO mixing ratio was 0.8 pptv. No correlation was found between IO and sea surface temperature, salinity, air temperature, wind speed or concentrations of chlorophyll-a. Measurements of I2 and the
sum of HOI + ICl during the cruise contributed to a steady-state analysis of the IO measurements. Production of IO was dominated by photolysis of I2, with a smaller but
significant contribution from photolysis of HOI. Reasonable agreement was found between measurements of IO made by LIF, MAX-DOAS, and satellite-based DOAS.
A laser-induced phosphorescence instrument for detection of glyoxal is in development. The results of initial testing are reported here. The instrument, which will be deployed
for field measurements in Cape Verde in 2014, has high sensitivity and a low 1 minute limit of detection (2.5 × 107 molecule cm−3 or 6.8 pptv), enabling detection of low
ambient mixing ratios of glyoxal.