Seasonal ozone production rate measurements by use of SAPHIR as a large continuous flow reactor during the JULIAC campaign

Abstract

<p>For the Jülich Atmospheric Chemistry Project campaign (JULIAC) at Forschungszentrum Jülich (FZJ), Germany, the atmospheric simulation chamber SAPHIR was used as a large photochemical flow reactor to study tropospheric chemistry in a rural environment. From an inlet at 50 m height above ground, ambient air was continuously fed through the chamber and exposed to natural solar radiation. A large set of instrumentation allowed for the measurement of NO, NO<sub>2</sub>, NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub>, HCHO, HONO, RO<sub>2</sub>, HO<sub>2</sub>, OH, k<sub>OH</sub>, CO, CO<sub>2</sub>, CH<sub>4</sub>, H2O, VOCs, aerosols, and O<sub>3</sub> in the sampled air. Intensive measurement phases were performed for one month in each season of 2019. One goal of the JULIAC project was to test our understanding of the chemistry of tropospheric ozone formation.</p><p>To determine the photochemical net ozone production rate in atmospheric air, O<sub>X</sub> (O<sub>3</sub> + NO<sub>2</sub>) was measured by commercial instruments at the inlet and inside the well mixed chamber. Through careful characterization of the flow reactor it is possible to predict a reference concentration of O<sub>X</sub> from the inflow measurements which excludes photochemistry. The measured O<sub>X</sub> concentration in the chamber was compared with the reference. At night, both concentrations agreed, but during daytime the chamber concentration was enhanced due to photochemical O<sub>X</sub> production. The difference was used to determine diurnal profiles of the net ozone production with 1 hour time resolution. Production rates up to 15 ppbv/h were observed with an accuracy of 1 ppb<sub>V</sub>/h. Uncertainties in the offsets of the instruments measuring at the inlet and inside the chamber were identified as large contributors (~0.5 ppb<sub>V</sub>/h) to the overall error. The measured net ozone production rates are compared to production rates that are expected from the reactions of peroxy radicals (HO<sub>2</sub>, RO<sub>2</sub>) with NO, all of which were concurrently measured. The analysis includes other chemical reactions that may produce or destroy ozone or NO<sub>2</sub> in the lower troposphere.</p><p>Good agreement (within 10%) between measured and calculated ozone production rates during the spring and summer campaigns confirms that the main contributions to daytime O<sub>X</sub> production and destruction in the troposphere are overall governed by the reactions of HO<sub>2</sub> and RO<sub>2</sub> with NO and the reaction of OH radicals with NO<sub>2</sub> in the rural environment studied in this project. The presentation will include a discussion of the role of the OH reactivity from VOCs for the local photochemical ozone production.</p>

Experimental chemical budgets of OH, HO2 and RO2 radicals in rural air in West-Germany during the JULIAC campaign 2019

“…In this work, the net production rate of OX (POx) was determined experimentally from the increase of OX in the sunlit SAPHIR chamber. Furthermore, measurements of radicals and NOX were used to calculate POx from the rate of OX formation reactions (Reaction R9, R10), and OX loss by the reaction of NO2 with OH (Reaction R12) (Mihelcic et al, 2003;Cazorla et al, 2012;Niether et al, 2022)):…”