11:00 AM - 1:00 PM
[AAS11-P12] Investigation of the sensitivity of ozone production to NOx and VOCs by means of smog chamber experiments
Keywords:photochemical oxidant, ozone, smog chamber, NOx, VOCs, chemical scheme
Tropospheric ozone known not only as an air pollutant but also recently as a short-lived climate forcer is produced by the photochemical reactions involving volatile organic compounds, VOCs, and NOx as precursors. Observation over decades has shown that although the concentrations of these precursors have decreased, the ozone concentration has increased. It has been recognized that ozone production depends nonlinearly on the precursors’ concentration, which is expected to give some explanations to the recent ozone trend. Accordingly, an accurate understanding of the chemical mechanism is required to estimate the contribution of the nonlinear dependence on the recent ozone trend and to predict the future trend for ozone mitigation control. Then, with the aim of obtaining an accurate chemical model to predict the sensitivity of ozone production to NOx and VOCs, in this study we examined the sensitivity of ozone production to NOx and VOCs during photochemical oxidation of propene using a NIES smog chamber as a first test case.
Experiments were performed at 1 atm and room temperature with the use of a 6m3 smog chamber equipped with a long optical path FT-IR. Propene (199–455 ppb) and NO (91–253 ppb) were introduced into the chamber as precursors. IPONO was (isopropyl nitrite, <7 ppb) also introduced as the OH radical source whose photolysis initiates the photochemical reaction. Then, a solar simulator was turned on to start irradiation and the photochemical reaction. Irradiation was conducted for from six to eight hours. The concentrations of reactants and products in the chamber were monitored by FT-IR every 15 minutes. A series of experiments were performed by changing the initial precursor concentrations, and, in several runs, additional propene or NO was introduced three hours after the irradiation started. The ozone production was evaluated by potential ozone formation (O3+NO2) and compared with a chemical model simulation.
The results qualitatively showed a typical ozone production dependence on the initial NO and propene. For example, with the initial concentration of propene being 400 ppb and NO being 100 ppb, the ozone production was NOx-controlled and the addition of NO raised the ozone production while adding VOC concentration had little influence on ozone production. On the other hand, with the initial concentration of propene being 200 ppb and NO being 200 ppb, ozone production was VOC-controlled and the addition of VOC raised the ozone production while the addition of NO resulted in a decrease in the ozone production. Furthermore, the results were quantitatively compared with model simulation, and its basic performance to predict the sensitivity of ozone production to NOx and VOCs was evaluated.
Experiments were performed at 1 atm and room temperature with the use of a 6m3 smog chamber equipped with a long optical path FT-IR. Propene (199–455 ppb) and NO (91–253 ppb) were introduced into the chamber as precursors. IPONO was (isopropyl nitrite, <7 ppb) also introduced as the OH radical source whose photolysis initiates the photochemical reaction. Then, a solar simulator was turned on to start irradiation and the photochemical reaction. Irradiation was conducted for from six to eight hours. The concentrations of reactants and products in the chamber were monitored by FT-IR every 15 minutes. A series of experiments were performed by changing the initial precursor concentrations, and, in several runs, additional propene or NO was introduced three hours after the irradiation started. The ozone production was evaluated by potential ozone formation (O3+NO2) and compared with a chemical model simulation.
The results qualitatively showed a typical ozone production dependence on the initial NO and propene. For example, with the initial concentration of propene being 400 ppb and NO being 100 ppb, the ozone production was NOx-controlled and the addition of NO raised the ozone production while adding VOC concentration had little influence on ozone production. On the other hand, with the initial concentration of propene being 200 ppb and NO being 200 ppb, ozone production was VOC-controlled and the addition of VOC raised the ozone production while the addition of NO resulted in a decrease in the ozone production. Furthermore, the results were quantitatively compared with model simulation, and its basic performance to predict the sensitivity of ozone production to NOx and VOCs was evaluated.