Abstract
The effect of the aerosol vertical distribution on photolysis frequencies of O3 and NO2 is studied. Aerosol measurements in Raciborz (50.08° N, 18.19° E), Poland, made using the CIMEL Sun photometer and collocated CHM-15k “Nimbus” ceilometer are analyzed for the period 2015–2020. Vertical profiles of the aerosol extinction are derived from the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm combining the ceilometer measurements of the aerosol backscattering coefficient with the collocated CIMEL measurements of the columnar characteristics of aerosols. The photolysis frequencies are calculated at the three levels in the lower troposphere (the surface and 0.5 and 2 km above the surface) using a radiative transfer model, Tropospheric Ultraviolet and Visible (TUV), for various settings of aerosol optical properties in the model input. The importance of the aerosol vertical distribution on photolysis frequencies is inferred by analyzing statistics of the differences between the output of the model, including the extinction profile from the GRASP algorithm, and the default TUV model (based on columnar aerosol characteristics by the CIMEL Sun photometer and Elterman’s extinction profile). For model levels above the surface, standard deviation, 2.5th percentile, 97.5th percentile, and the extremes, calculated from relative differences between these input settings, are comparable with the pertaining statistical values for the input pair providing changes of photolysis frequencies only due to the variability of the columnar aerosol characteristics. This indicates that the vertical properties of aerosols affect the distribution of the photolysis frequencies in the lower troposphere on a similar scale to that due to variations in columnar aerosol characteristics.
Highlights
We present a model study of the aerosol effects on two key photolysis frequencies, j (O1 D) and j (NO2 ), using the α-profile derived from the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm, combining the ceilometer measurements of the aerosol backscattering coefficient with the collocated CIMEL measurements of columnar characteristics of aerosols
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Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The important parameters affecting photolysis frequencies are solar zenith angle (SZA), clouds, aerosol optical characteristics (AOCs), surface albedo, column content of ozone, and altitude [23,24]. We present a model study of the aerosol effects on two key photolysis frequencies, j (O1 D) and j (NO2 ), using the α-profile derived from the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm, combining the ceilometer measurements of the aerosol backscattering coefficient with the collocated CIMEL measurements of columnar characteristics of aerosols. The j values for the three levels in the lower troposphere (the surface, 0.5 km and 2 km above surface) were analyzed based on the TUV model simulations with different AOC input settings to find out the importance of the vertical distribution of AOC on the photolysis rate
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