Chemical processes related to net ozone tendencies in the free troposphere
Ozone (O<sub>3</sub>) is an important atmospheric oxidant, a greenhouse gas, and a hazard to human health and agriculture. Here we describe airborne in situ measurements and model simulations of O<sub>3</sub> and its precursors during tropical and extratropical field campa...
Main Authors: | , , , , , , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-09-01
|
Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/17/10565/2017/acp-17-10565-2017.pdf |
Summary: | Ozone (O<sub>3</sub>) is an important atmospheric oxidant, a greenhouse
gas, and a hazard to human health and agriculture. Here we describe airborne
in situ measurements and model simulations of O<sub>3</sub> and its precursors
during tropical and extratropical field campaigns over South America and
Europe, respectively. Using the measurements, net ozone formation/destruction
tendencies are calculated and compared to 3-D chemistry–transport model
simulations. In general, observation-based net ozone tendencies are positive
in the continental boundary layer and the upper troposphere at altitudes
above ∼ 6 km in both environments. On the other hand, in the
marine boundary layer and the middle troposphere, from the top of the
boundary layer to about 6–8 km altitude, net O<sub>3</sub> destruction prevails.
The ozone tendencies are controlled by ambient concentrations of nitrogen
oxides (NO<sub><i>x</i></sub>). In regions with net ozone destruction the available
NO<sub><i>x</i></sub> is below the threshold value at which production and destruction of
O<sub>3</sub> balance. While threshold NO values increase with altitude, in the
upper troposphere NO<sub><i>x</i></sub> concentrations are generally higher due to the
integral effect of convective precursor transport from the boundary layer,
downward transport from the stratosphere and NO<sub><i>x</i></sub> produced by lightning.
Two case studies indicate that in fresh convective outflow of electrified
thunderstorms net ozone production is enhanced by a factor 5–6 compared to
the undisturbed upper tropospheric background. The chemistry–transport model
MATCH-MPIC generally reproduces the pattern of observation-based net ozone
tendencies but mostly underestimates the magnitude of the net tendency (for
both net ozone production and destruction). |
---|---|
ISSN: | 1680-7316 1680-7324 |