Measurements of HOx and Other Species in a Mid-Latitude Deciduous Forest

HO_x radicals are critically important to tropospheric chemical cycles that oxidize emitted species and lead to production of ozone, growth of aerosols, and presence of oxidized organic compounds. Measurements of OH, HO₂, and RO₂, along with accurate and comprehensive observations of species and processes that control their concentrations, provide important tests of current understanding of detailed chemistry.

Important to establishing confidence in the difficult measurements of these short-lived, hard-to-sample species is the comparison of measurements using different observational techniques. An expert group of scientists involved in measurements of HOx and related species has recommended conducting informal intercomparisons among small groups eventually leading to one or more large comprehensive, formal intercomparisons (Hofzumahaus and Heard, 2016). We conducted informal comparisons in two summers: (1) at the PROPHET site in northern Michigan in 2016 as part of PROPHET-AMOS, and (2) at the Indiana University Research and Teaching Preserve (IURTP) in 2017.

Described here are the results of ambient measurements during the summer of 2017 using the University of Colorado instruments that included two quadrupole CIMS (chemical ionization mass spectrometers) for peroxy radicals and OH, and a nitrate-CIMS time-of-flight instrument (NO3-ToF-CIMS) that observed highly oxidized organic compounds and peroxy radicals. The ambient measurements will be compared with results from a constrained steady-state box model. Initial results from the intercomparisons are shown in other presentations (Reidy et al.; Rosales et al.).

Reference:

Hofzumahaus, A., and D. Heard, Assessment of local HOx and ROx Measurement Techniques: Achievements, Challenges, and Future Directions, Report of International HOx Workshop 2015, Forschungszentrum Julich, April, 2016.