Actinometer and Eppley radiometer measurements of the NO₂ photolysis rate coefficient during the Mauna Loa Observatory photochemistry experiment

Abstract

Measurements of the apparent first‐order rate coefficient for NO2 photodissociation (jNO2) were made using a chemical actinometer during the month of May 1988 at the Mauna Loa Observatory, Hawaii. Simultaneous measurements of the ultraviolet irradiance (E), obtained with an Eppley radiometer, allowed extensive testing of the semi‐empirical relationships between E and jNO2 proposed by Madronich (1987a). More than 3700 simultaneous measurements of jNO2 and E were obtained for solar zenith angles ranging from 4–90 degrees, and for different sky conditions (including clear skies, partial cloud cover, arid valley clouds below the horizon). For overhead clear skies, the NO2 photodissociation rate coefficient derived from Eppley radiometer data, here denoted j′, was in good agreement with actinometric measurements, j′/jNO2=1.01±0.05(1σ). The actinometer‐radiometer relationship holds reasonably well even when low‐lying valley clouds are present. For the periods of overhead intermittent clouds, the j′values track jNO2 values well, but the observed ratio shows significantly more scatter and the average is somewhat less than unity: 0.93 ± 0.09 (1σ). Measurements taken with and without upward scattered and reflected radiation show that valley clouds can contribute to the jNO2 values for the conditions encountered during the Mauna Loa Observatory Photochemistry Experiment.

Measurements of the HONO photodissociation constant

“…As a result, the direct measurement of j is preferred. Only chemical actinometers (Junkermann et aI., 1989;Shetter et al, 1992) directly measure photodissociation frequencies, by observing the respective photochemical process inside a closed UV-transparent cell. The decay of the reactant or the formation of products during a given time of exposure is then a measure of the respective j value.…”

The effects of parametric uncertainties in simulations of a reactive plume using a Lagrangian stochastic model

“…The maximum and minimum values for the Arrhenius parameters are in accordance with Atkinson et al (2004). The uncertainty ranges for the photolysis rates are obtained from Shetter et al (1992) and Shetter et al (1996). Uncertainties for the temperature were assumed to be within the range of [273…293]K. The range for NO fraction in the source (initial concentration [NO]=1.26x10 16 molcm -3 ) was varied from 1 to 0.8 in order to assess the impact of uncertainties of primary NO 2 in NO x sources which is also of relevance to transport related emissions of NO x .…”

“…7 from Shetter et al (1996) and no. 8 from Shetter et al (1992). The HDMR software package (Ziehn and Tomlin, 2008c) has been applied in order to perform global sensitivity analysis and to calculate variance based sensitivity indices for the 22 input parameters based on the uncertainty ranges described above.…”

NO<sub>2</sub> and HCHO photolysis frequencies from irradiance measurements in Thessaloniki, Greece

“…In the past, chemical actinometers and filter radiometers have been used to measure J(NO 2 ) (e.g. Dickerson et al, 1982;Shetter et al, 1992;Lantz et al, 1996;Balis et al, 2002;Shetter at al., 2003). Similar measurements for other photolysis rates such as J(HCHO), were not as common as in the case of NO 2 or O 3 , due to considerable requirements concerning the development and maintenance of these instruments, so those rates were either estimated or modeled (Kraus and Hofzumahaus, 1998).…”