Abstract
Abstract. We apply a novel experimental procedure for the rapid measurement of the average volume mixing ratios (VMRs) and horizontal distributions of trace gases such as NO2, SO2, and HCHO in the boundary layer, which was recently suggested by Sinreich et al. (2013). The method is based on two-dimensional scanning multi-axis differential optical absorption spectroscopy (MAX-DOAS). It makes use of two facts (Sinreich et al., 2013): first, the light path for observations at 1° elevation angle traverses mainly air masses located close to the ground (typically < 200 m); second, the light path length can be calculated using the simultaneous measured absorption of the oxygen dimer O4. Thus, the average value of the trace gas VMR in the atmospheric layer between the surface and the particular altitude, for which this observation was sensitive, can be calculated. Compared to the originally proposed method, we introduce several important modifications and improvements: We apply the method only to measurements at 1° elevation angle (besides zenith view), for which the uncertainties of the retrieved values of the VMRs and surface extinctions are especially small. Using only 1° elevation angle for off-axis observation also allows an increased temporal resolution. We determine (and apply) correction factors (and their uncertainties) directly as function of the measured O4 absorption. Finally, the method is extended to trace gases analysed at other wavelengths and also to the retrieval of aerosol extinction. Depending on atmospheric visibility, the typical uncertainty of the results ranges from about 20% to 30%. We apply the rapid method to observations of a newly-developed ground-based multifunctional passive differential optical absorption spectroscopy (GM-DOAS) instrument in the north-west outskirts near Hefei in China. We report NO2, SO2, and HCHO VMRs and aerosol extinction for four azimuth angles and compare these results with those from simultaneous long-path DOAS observations. Good agreement is found (squares of the correlation coefficients for NO2, SO2, and HCHO were 0.92, 0.85, and 0.60, respectively), verifying the reliability of this novel method. Similar agreement is found for the comparison of the aerosol extinction with results from visibility meters. Future studies may conduct measurements using a larger number of azimuth angles to increase the spatial resolution.
Highlights
Nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) are important atmospheric constituents which play crucial roles in tropospheric chemistry (Crutzen, 1979; Lurmann et al, 1992; Ho et al, 2002; Hellén et al, 2004; Smith et al, 2011)
The method is extended to trace gases analysed at other wavelengths and to the retrieval of aerosol extinction
Note that the effective light path length derived in Eq (1) is representative for 360 nm because it was derived from the O4 absorption band at 360 nm. It can be transformed for other wavelength ranges of 340 nm and 310 nm using Eqs. (6) and (7). Using this effective light path length derived in Eq (1), the average trace gas concentration near the ground can be calculated from the derived trace gas differential slant column density (dSCD): c = dSCD/L
Summary
Nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) are important atmospheric constituents which play crucial roles in tropospheric chemistry (Crutzen, 1979; Lurmann et al, 1992; Ho et al, 2002; Hellén et al, 2004; Smith et al, 2011). Concentration profiles of trace gases and aerosol extinction in the boundary layer can be derived from MAX-DOAS observations using different inversion techniques, e.g. the optimal estimation method (Frieß et al, 2006, 2011; Yilmaz, 2012) or a look-up table approach (Li et al, 2010, 2013; Wagner et al, 2011). Using this effective light path length derived in Eq (1), the average trace gas concentration (and from that the VMR) near the ground can be calculated from the derived trace gas dSCD: It was shown by Sinreich et al (2013) that using this simple retrieval scheme, systematic errors are introduced, if the relative profile of the considered trace gas differs from that of O4. They are usually between 20 % and 30 % (see Sect. 2.2)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
