Open AccessDerivation of tropospheric NO 3 profiles using off‐axis differential optical absorption spectroscopy measurements during sunrise and comparison with simulations
Author(s) -
von Friedeburg Christoph,
Wagner Thomas,
Geyer Andreas,
Kaiser Norbert,
Vogel Bernhard,
Vogel Heike,
Platt Ulrich
Publication year - 2002
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd000481
Subject(s) - sunrise , differential optical absorption spectroscopy , troposphere , atmospheric sciences , planetary boundary layer , environmental science , radiative transfer , atmospheric radiative transfer codes , absorption (acoustics) , boundary layer , meteorology , geology , physics , optics , thermodynamics
Early morning vertical profiles of tropospheric NO 3 were derived by spectroscopy of scattered sunlight in off‐axis geometry during sunrise. The measurements were carried out in the urban area of Heidelberg, Germany (April, July, and August 1999). The retrieval algorithm is based on the nitrate radical's rapid photolysis during sunrise, radiative transfer, as well photochemical modeling. We derived NO 3 near‐ground concentrations of typically (0.2–18) × 10 7 cm −3 , concentrations above 3 km of (5–50) × 10 7 cm −3 , and a NO 3 maximum at a height of ∼350 m with concentrations of (100–900) × 10 7 cm −3 . Assuming the case of very high terpene levels even at higher altitudes, which is very unlikely for the atmospheric conditions during the measurements, we obtain a different mathematical solution of our inversion problem yielding the NO 3 maximum at altitudes of ∼2.5 km. The enriched layer was found to hold the bulk of the tropospheric nighttime NO 3 . The retrieved profile confirms earlier suggestions that ground‐level measurements may be significantly underestimating the oxidative capacity of the boundary layer under stable nocturnal conditions. The NO 3 layer is probably formed as a result of the vertical profiles of the NO 3 educts (NO 2 and O 3 ), with NO 2 concentrations falling off more slowly with height than the NO 3 scavengers, e.g., anthropogenic NO as well as volatile organic compounds emitted at ground level. Independently from these measurements model simulations with a comprehensive three‐dimensional model system were performed for an area, which includes the measurement site. A pronounced maximum (3.3 × 10 9 cm −3 ) of the nocturnal NO 3 concentration was found at ∼250 m above the surface, i.e., at the top of the nocturnal stable boundary layer. The average NO 3 concentration close to the surface was 5 × 10 7 cm −3 . The only significant difference between the observations and the model results was a steeper decrease of the NO 3 concentration above the maximum of the observed profiles.