NO<sub>2</sub> and HCHO photolysis frequencies from irradiance measurements in Thessaloniki, Greece

Abstract

Abstract. An empirical approach for the retrieval of nitrogen dioxide (NO 2 ) and formaldehyde (HCHO) photolysis frequencies from measurements of global irradiance is presented in this work. Four months of synchronous measurements of actinic flux and global irradiance performed in Thessaloniki, Greece by a Bentham spectroradiometer were used to extract polynomials for the conversion of global irradiance to photolysis frequencies [J(NO 2 ) and J(HCHO)]. The comparison of these photolysis frequency values to the corresponding values calculated by spectral actinic flux measurements, showed a ratio very close to unity for all J's with a standard deviation of 12% (2σ ) for J(NO 2 ) and 6% (2σ ) for J(HCHO). Additional sets of polynomials were also extracted to allow determination of J(NO 2 ) by spectroradiometers with lower upper wavelength limits such as single and double Brewer spectroradiometers within acceptable uncertainty (corresponding ratio was 1 and standard deviation was 12% (2σ ) for the method that can be used with double Brewers and 20% for the method that can be used for single Brewers). The validity of the method under different atmospheric conditions was also examined by applying the polynomials to another set of actinic flux and global irradiance measurements performed in May 2004, in Buchhofen, Germany. In this case, comparing J values extracted from the polynomials to those calculated from actinic flux, showed equivalent results, demonstrating that the method can also be applied to other measurement sites.

Changes in tropospheric composition and air quality due to stratospheric ozone depletion and climate change

“…Methods have now been developed for converting irradiance to actinic flux. [27][28][29][30][31][32] The uncertainty in irradiance-derived actinic flux for J(O 1 D) is greater than for directly measured values. The uncertainty in the conversion of irradiance into actinic flux depends on the solar zenith angle, wavelength, and ambient conditions, but can be as low as 7% (95% confidence).…”

“…There are two different routes for decay, and the rate of both routes will depend on stratospheric ozone. Methods for deriving the photolysis rate from irradiance have been proposed, 32 although to date such estimates have not been widely used.…”

Estimation of photolysis frequencies from TOMS satellite measurements and routine meteorological observations

“…To apply this method we selected irradiance at certain wavelengths which are representative of the spectral regions of interest for these two frequencies, namely 305 nm and 380 nm. The method presented in the two previous publications (Kazadzis et al, 2004;Topaloglou et al, 2005) is an approach for the retrieval of J(NO 2 ) and J(O 1 D) photolysis frequencies from measurements of surface global irradiance.…”

“…The TOMS spectral irradiance is converted to J(O 1 D) and J(NO 2 ) photolysis frequencies, using the methodology established by Kazadzis et al (2004) and Topaloglou et al (2005). To apply this method we selected irradiance at certain wavelengths which are representative of the spectral regions of interest for these two frequencies, namely 305 nm and 380 nm.…”

“…Several methods include conversion of ground-based (GB) measurements of irradiance to actinic flux, which is then used for the photolysis frequency calculation (Van Weele at al., 1995;Cotté et al, 1997;Kazadzis et al, 2000;Webb et al, 2002b;Kylling et al, 2003;Schallhart et al, 2004) while more recent work introduces the direct calculation of photolysis frequencies from irradiance from empirical relationships (McKenzie et al, 2002;Seroji et al, 2004;Kazadzis et al, 2004;Topaloglou et al, 2005).…”