Absorption cross-sections of NO2: simulation of temperature and pressure effects

Abstract

The measurements of the NO 2 absorption cross sections by several authors have been considered in order to derive its temperature and pressure dependences in the 13 200 -42 000 cm −1 spectral range. The temperature dependence is assumed to be linear in the temperature range investigated (217.0 -298:5 K), whereas the in uence of the total pressure is expressed as a temperature-dependent broadening coe cient. From measurements performed with mixtures of NO 2 in air and in N 2 , values of 0 air (296 K) and 0 N2 (296 K) were found to be, respectively, 0:081 ± 0:002 and 0:069 ± 0:003 cm −1 atm −1 . The temperature coe cient n obtained in the present work is 0:8 ± 0:1. The parameterization of the cross sections developed in this work can reproduce measured cross sections within 4%. ?

The use of NO<sub>2</sub> absorption cross section temperature sensitivity to derive NO<sub>2</sub> profile temperature and stratospheric–tropospheric column partitioning from visible direct-sun DOAS measurements

“…The temperature-dependent NO 2 cross section, σ , in UV and visible wavelength regions can be calculated at any T , using a linear regression model (Vandaele et al, 2003) (Eq. 1).…”

“…Figure 3 shows the high-resolution (0.1 cm −1 ; Vandaele et al, 2003) laboratory σ 0 (λ) at 273 K and α(λ) convolved with the MFDOAS instrument transfer function (FWHM 0.83 nm/40.91 cm −1 at 450 nm). While the atmospheric NO 2 profile spans an altitude range with a significant pressure gradient, the pressure effect on σ (λ) is not present at spectral resolution λ > 2 cm −1 (0.04 at 450 nm; Vandaele et al, 2003). Since most DOAS systems have much lower spectral resolution ( λ > 0.4 nm/FWHM), the effect of pressure is ignored in this analysis.…”

“…T was derived using the Vandaele et al (2003) linear regression model at T 0 = 220 K. The stratospheric NO 2 profile effective temperature was taken from atmospheric soundings or ozonesondes at 27 km. Tropospheric temperature was approximated as surface temperature.…”

“…-the sentence was rearranged. In this study we linearly interpolate Vandaele et al (2003) NO 2 cross sections at 220 and 298 K to the desired temperatures. Fitting a constant temperature cross section results in biases that are pollution and temperature dependent.…”

“…This paper presents a temperature sensitivity method (TESEM) to accurately calculate total vertical NO 2 column, atmospheric slant NO 2 profile-weighted temperature (T ), and to separate stratospheric and tropospheric columns from direct-sun (DS), ground-based measurements using the retrieved T . TESEM is based on differential optical absorption spectroscopy (DOAS) fitting of the linear temperature-dependent NO 2 absorption cross section, σ (T ), regression model (Vandaele et al, 2003). Separation between stratospheric and tropospheric columns is based on the primarily bimodal vertical distribution of NO 2 and an assumption that stratospheric effective temperature can be represented by temperature at 27 km ± 3 K, and tropospheric effective temperature is equal to surface temperature within 3-5 K. These assumptions were derived from the Global Modeling Initiative (GMI) chemistry-transport model (CTM) simulations over…”