HR: 1340h
AN: A33D-1532    [Abstracts]
TI: Influence of Nocturnal Vertical Stability on Daytime Chemistry: A One-dimensional Model Study
AU: * Wong, K
EM: clare@atmos.ucla.edu
AF: UCLA Atmospheric and Oceanic Sciences, Mathematical Sciences Building 7127, Los Angeles, CA 90095, United States
AU: Stutz, J
EM: jochen@atmos.ucla.edu
AF: UCLA Atmospheric and Oceanic Sciences, Mathematical Sciences Building 7127, Los Angeles, CA 90095, United States
AB: Nocturnal chemistry can play an important role in determining the initial conditions for photochemistry of the next day, through the chemical removal and conversion of air pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOC). The quantification of these processes is challenging because radiation cooling leads to the suppression of turbulence and vertical mixing. Consequently, emissions at the ground are only slowly transported vertically and vertical concentration gradients develop for many trace gases, making nocturnal chemistry dependent on altitude and vertical stability. The stable nocturnal boundary layer which is often capped by a neutrally stratified residual layer breaks up after sunrise and a vertically well-mixed boundary layer forms. The transition from a vertically non-uniform chemical regime to a well-mixed boundary layer makes the assessment of the influence of nocturnal vertical stability on daytime chemistry challenging. Here we present one-dimensional (1-D) chemical transport model calculations for different nighttime vertical stability (stable, weakly stable and neutral) and different O₃ formation regimes, i.e. NOx- vs VOC-sensitive. We investigate the influence of nocturnal vertical stability on O₃ formation during the next day by analyzing the vertically integrated nocturnal loss of NOx, and the concentrations of NOx and O₃ during the next day. Our results show that the impact of nocturnal chemistry depends on whether O₃ formation occurs under NOx- or VOC-sensitive conditions.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting