Stratospheric NO₂: 1. Observational method and behavior at mid‐latitude

Abstract

This paper describes a method for obtaining the abundance and altitude of stratospheric NO• by using ground-based spectroscopy at twilight. The method is then used to study the behavior of NO• over Colorado at 40øN; a companion paper discussed observations elsewhere. Large changes in both the abundance of NO• and in its diurnal variation are commonly seen at mid-latitude and appear to reflect the role of quasi-horizontal transport in the stratosphere on a global scale. stratosphere and its center of mass in altitude. Since the density of NO2 changes during the twilight period, we discuss how this affects the interpretation; the abundance is greater at night than in daytime, since sunlight dissociates NO2 into a mixture of NO and NO2. We then discuss the limits and errors associated with this method for determining the abundance and vertical distribution of NO2 in the stratosphere.As in the earlier work [Noxon, 1975], we employed a scanning spectrometer operated at a resolution of 7 A (not the 5 .• incorrectly stated there); instrumental details are described in the earlier paper. Even a simple spectrometer is adequate for such work owing to the relatively strong intensity of the twilight sky and the lack of any requirement for high spectral resolution. Figure I shows at the top two spectra of the zenith Paper number 9C0466. 5047 5048 NOXON ET AL.: STRATOSPHERIC NO•.

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

“…Passive differential optical absorption spectroscopy (DOAS) has been successfully applied since the 1970s to retrieve numerous trace gases, including NO 2 , from ground-based and satellite instruments (Noxon, 1975;Noxon et al, 1979;Mount et al, 1987;Solomon et al, 1987;Platt et al, 1979;Platt, 1994;Plane and Smith, 1995). While all passive DOAS measurements contain information about gas absorption at all atmospheric altitudes, different observation geometries have been developed to optimize the sensitivity of the passive DOAS instruments to trace gas amounts located in various layers of the atmosphere.…”

“…The "traditional" ground-based DOAS technique employs a zenith-looking instrument to measure scattered sunlight (Noxon, 1975;Noxon et al, 1979), and is mainly sensitive to stratospheric and upper tropospheric absorbers, especially at large solar zenith angles (SZA > 85 • ). Vertical stratospheric NO 2 profiles during sunset/sunrise were derived from zenith sky (e.g., McKenzie et al, 1991;Preston et al, 1997;Hendrick et al, 2004) and balloon DOAS measurements (e.g., Pommereau and Piquard, 1994;Butz et al, 2006;Kritten et al, 2010).…”

Comparison of box-air-mass-factors and radiances for Multiple-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) geometries calculated from different UV/visible radiative transfer models

“…In contrast to the well established ground based observations of zenithscattered sun light (Noxon et al, 1979;Solomon et al, 1987), MAX-DOAS observations are directed into the illuminated atmosphere under various elevation angles. Since for a slant viewing geometry, the absorption paths through (and accordingly the AMFs for) the lower atmosphere can become rather large, MAX-DOAS observations are especially sensitive to tropospheric trace gases.…”

“…For the interpretation of remote sensing measurements, however, the most important output is a measure for their sensitivity to atmospheric trace gases. Usually the sensitivity is expressed as so called Air Mass Factor (AMF) (Noxon et al, 1979;Solomon et al, 1987;Perliski and Solomon, 1993), which is defined as the ratio of the measured slant column density (SCD) and the vertical column density (VCD, the vertically integrated concentration):…”

Mobile MAX-DOAS observations of tropospheric trace gases

“…For that purpose, a so called air mass factor (AMF) is applied (Noxon et al, 1979;Solomon et al, 1987;Marquard et al, 2000), which is defined as the ratio of the (total) SCD and (total) VCD:…”