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In September 2016 the IAP instrument participated in the CINDI-2 campaign, held in the Netherlands. CINDI 2 (2nd Cabauw Intercomparison of Nitrogen Dioxide Measuring Instruments) involves about 40 instruments quasi-synchronously performing DOAS measurements of NO2 and other trace gases.
During the campaign the instrument ports had telescopes A and B with similar field of view of about 0.3°. Telescope A was always directed to the zenith. Telescope B was directed at 5° elevation angle. Two gratings were installed in the spectrometer. They provide different spectral resolution (FWHM ~0.4 and 0.8 nm respectively) and spectral window width (~70 and ~140 nm respectively). During CINDI-2 campaign we performed test measurements in UV and visible wavelength ranges to investigate instrument stability and retrieval errors of NO2 and HCHO contents.
We perform the preliminary error analysis of retrieval of the NO2 and HCHO differential slant column densities using spectra measured in four modes of the instrument basing on residual noise analysis in this paper. It was found that rotation of grating turret does not significantly affected on quality of NO2 DSCD retrieval from spectra which measured in visible spectral region. Influence of grating turret rotation is much more significant for gas DSCD retrieval from spectra which measured in UV spectral region. Standard deviation of retrieval error points to presence of some systematic error.
HCHO has a sufficiently large absorption cross-section in the UV spectral region to be detected by the technique of the differential optical absorption spectroscopy (DOAS). We present here new version 1.3a of the algorithm for retrieval of the HCHO total content in the troposphere from DOAS observations of the scattered solar radiation developed in A.M. Obukhov Institute of Atmospheric Physics (IAP). The new version has reduced retrieval error but negligible bias with respect to the previous versions. DOAS measurements of scattered solar radiation are performed at Zvenigorod Scientific Station (ZSS, 55°41'49''N, 36°46'29''E) located in 38 km west from Moscow Ring Road by a MAX-DOAS instrument since 2008. We provide preliminary results of the HCHO total content measurements in the troposphere observed in 2010-2012 obtained by the revised retrieval algorithm.
For analysis of the HCHO variability we selected spectra taken in cloud free conditions. Version 1.2 of retrieval algorithm is used. It uses information on the surface albedo and the height of the atmospheric boundary layer inferred from a model. Data screening using color index was implemented. The obtained data quantify the Moscow megapolis influence on air quality at Zvenigorod by comparison of HCHO VCD for east and west wind directions. HCHO VCD for east winds is grater one for west winds for 0.5×1016 mol×cm-2 in average. Strong dependence of HCHO VCD on air temperature is noticeable in our data for air temperatures from +5 to +35°C. In different conditions of the atmosphere gradient of the temperature effect is about 1.1–1.2×1015 mol×cm-2×°C-1. The increase of the formaldehyde content with the increase of the air temperature can be caused by the HCHO formation from non-methane biogenic volatile organic compounds for which more emission is expected at higher temperatures.
Measurements of formaldehyde total content using DOAS technique: a new retrieval method for overcast
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