Abstract
Abstract. This paper presents a temperature sensitivity method (TESEM) to accurately calculate total vertical NO2 column, atmospheric slant NO2 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 NO2 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 NO2 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 two northern midlatitude sites in 2011. TESEM was applied to the Washington State University Multi-Function DOAS instrument (MFDOAS) measurements at four midlatitude locations with low and moderate NO2 anthropogenic emissions: (1) the Jet Propulsion Laboratory's Table Mountain Facility (JPL-TMF), CA, USA (34.38° N/117.68° W); (2) Pullman, WA, USA (46.73° N/117.17° W); (3) Greenbelt, MD, USA (38.99° N/76.84° W); and (4) Cabauw, the Netherlands (51.97° N/4.93° E) during July 2007, June–July 2009, July–August and October 2011, November 2012–May 2013, respectively. NO2 T and total, stratospheric, and tropospheric NO2 vertical columns were determined over each site.
Highlights
1.1 NO2 importanceActive nitrogen oxides (NOx = NO + NO2) play an important role in atmospheric chemistry
The main goal of this section is to demonstrate that temperature sensitivity method (TESEM) accurately calculates total NO2 SCD at profile T and provides a reasonable estimation of stratospheric and tropospheric columns based on retrieved NO2 slant profile effective temperature from DS differential optical absorption spectroscopy (DOAS) observations. It compares DS DOAS retrievals from TESEM and traditional DOAS fitting methods
Since the quality of the DOAS spectral fit greatly impacts the success of TESEM, we first show the optical depth (OD) of gaseous absorbers fitted by QDOAS software for two sites: Jet Propulsion Laboratory’s Table Mountain Facility (JPL-TMF) and NASA/GSFC
Summary
Active nitrogen oxides (NOx = NO + NO2) play an important role in atmospheric chemistry. They catalyze ozone destruction in the stratosphere, activate ozone production in the lower troposphere, and influence the HOx budget. NOx is efficiently removed from the lower troposphere (lifetime 3–10 h in the tropics and summer northern midlatitudes, increasing to 48 h in winter at high latitudes) mainly by wet and dry deposition of HNO3 (Martin et al, 2003). The NOx lifetime in the free troposphere is longer (5–10 days), mainly due to lower humidity levels (Wenig et al, 2003). The lower troposphere NOx lifetime allows for transport on a regional scale (up to 100 km). Long-range transport of NOx introduced into the free troposphere from the planetary boundary layer (PBL) has been observed (Parrish et al, 2004; Wenig et al, 2003)
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