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Photochemical regimes in urban atmospheres: The influence of dispersion
Author(s) -
Honoré Cécile,
Vautard Robert,
Beekmann Matthias
Publication year - 2000
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl011050
Subject(s) - atmosphere (unit) , diurnal cycle , forcing (mathematics) , dispersion (optics) , environmental science , atmospheric sciences , diurnal temperature variation , range (aeronautics) , meteorology , materials science , physics , optics , composite material
The dependence on emissions of urban photochemistry is studied under meteorological conditions favouring pollution episodes. We use a simple chemistry‐transport model, yet realistic with respect to the main chemical and physical processes and considering the diurnal cycle of forcing parameters. For a range of NO x emissions, the diurnal equilibria of the system are searched for. It is shown that, if the photochemistry over a large city mostly exhibits a negative sensitivity to NO x emissions, there are meteorological situations under which it becomes (positively) NO x sensitive, the dispersion time scale being a key parameter. We show that, under specific conditions, the urban atmosphere might reach two very different diurnal equilibria. We demonstrate that the sensitivity to NO x emissions evolves with time: under specific conditions, the urban atmosphere becomes NO x sensitive within two days.