4:00 PM - 4:15 PM
[AAS09-21] Quantifying net production rates of tropospheric ozone by using the triple oxygen isotopes of nitrogen oxides as tracers
Keywords:ozone, nitric oxide, nitrogen dioxide, Δ17O
Tropospheric ozone (O3) is the third largest contributor to greenhouse radiative forcing after carbon dioxide and methane. Besides, O3 is one of the most important oxidizing species in the atmosphere, so that it has multiple negative impacts on the atmospheric environment, humans, ecosystems, and the climate. Consequently, it is necessary to quantitatively understand the origin and the formation pathways of tropospheric O3.
Tropospheric O3 is supplied through two basic processes: downward flux from the stratosphere, and in situ production through the photodissociation of nitrogen dioxide (NO2) into nitric oxide (NO). In the clean air where the reaction between NO and O3 is responsible for the production of NO2, however, net production of O3 is zero, so that net ozone production is limited to the polluted air, where the reaction between NO and peroxy radicals (HO2 and RO2) is responsible for the production of NO2. Therefore, to quantify ozone production in each atmospheric environment, not only the photodissociation rate of NO2, which can be estimated from the concentration of NO2 and the irradiance (solar radiation), but also the contribution of chemical reactions between NO and HO2+RO2 in the production of NO2 in the atmosphere should be clarified.
Therefore, this study quantitatively assessed the contribution of the HO2+RO2 reaction to the formation of NO2 in the atmosphere, using the Δ17O value (Δ17O = δ17O – 0.52 × δ18O), which represents the relative composition of three oxygen isotopes (16O, 17O, and 18O) in NOx (NO2 + NO). Additionally, an attempt was made to estimate the net O3 production rate by multiplying the contribution rate of the HO2+RO2 reaction by the total O3 production rate estimated from the photodissociation rate of NO2.
Observations were conducted at two locations, namely Wakamiya-Odori Park in Nagoya City (urban area) and the Nagoya University campus (suburban area), during both day and night. The multi-stage filter pack method was used, where specific filters for each compound, soaked in collection solution. The atmospheric air was passed through the filters using a pump, simultaneously capturing various nitrogen oxide compounds (NO, NO, HNO3, HONO, etc.) in the form of NO2-. The filters were extracted with ultrapure water, reduced to N2O, and introduced into a mass spectrometer via online thermal decomposition to measure the Δ17O value.
The Δ17O values of NO and NO2 in Nagoya exhibited significantly higher values than 0‰ at both urban and suburban locations, confirming the contribution of O3 (Δ17O = +36 to 37 ‰). to their respective formation reactions. Furthermore, a comparison of the Δ17O values of NO and NO2 revealed the involvement of both O3 and HO2+RO2 in the oxidation process of NO to NO2 at both locations. The estimated contribution rate of the HO2+RO2 reaction to the formation of NO2 indicated a contribution of approximately 40% in the urban area and about 30% in the suburban area. This presentation will also discuss the calculated O3 production rates based on these results.
Tropospheric O3 is supplied through two basic processes: downward flux from the stratosphere, and in situ production through the photodissociation of nitrogen dioxide (NO2) into nitric oxide (NO). In the clean air where the reaction between NO and O3 is responsible for the production of NO2, however, net production of O3 is zero, so that net ozone production is limited to the polluted air, where the reaction between NO and peroxy radicals (HO2 and RO2) is responsible for the production of NO2. Therefore, to quantify ozone production in each atmospheric environment, not only the photodissociation rate of NO2, which can be estimated from the concentration of NO2 and the irradiance (solar radiation), but also the contribution of chemical reactions between NO and HO2+RO2 in the production of NO2 in the atmosphere should be clarified.
Therefore, this study quantitatively assessed the contribution of the HO2+RO2 reaction to the formation of NO2 in the atmosphere, using the Δ17O value (Δ17O = δ17O – 0.52 × δ18O), which represents the relative composition of three oxygen isotopes (16O, 17O, and 18O) in NOx (NO2 + NO). Additionally, an attempt was made to estimate the net O3 production rate by multiplying the contribution rate of the HO2+RO2 reaction by the total O3 production rate estimated from the photodissociation rate of NO2.
Observations were conducted at two locations, namely Wakamiya-Odori Park in Nagoya City (urban area) and the Nagoya University campus (suburban area), during both day and night. The multi-stage filter pack method was used, where specific filters for each compound, soaked in collection solution. The atmospheric air was passed through the filters using a pump, simultaneously capturing various nitrogen oxide compounds (NO, NO, HNO3, HONO, etc.) in the form of NO2-. The filters were extracted with ultrapure water, reduced to N2O, and introduced into a mass spectrometer via online thermal decomposition to measure the Δ17O value.
The Δ17O values of NO and NO2 in Nagoya exhibited significantly higher values than 0‰ at both urban and suburban locations, confirming the contribution of O3 (Δ17O = +36 to 37 ‰). to their respective formation reactions. Furthermore, a comparison of the Δ17O values of NO and NO2 revealed the involvement of both O3 and HO2+RO2 in the oxidation process of NO to NO2 at both locations. The estimated contribution rate of the HO2+RO2 reaction to the formation of NO2 indicated a contribution of approximately 40% in the urban area and about 30% in the suburban area. This presentation will also discuss the calculated O3 production rates based on these results.