richard t. mcnider atmospheric sciences department university of alabama in huntsville...
TRANSCRIPT
Richard T. McNider
Atmospheric Sciences Department
University of Alabama in Huntsville
The Role of the Physical Atmosphere in Air Quality Impacts
Use of Satellite Data to Improve the Physical Atmosphere in Air Quality
Decision Models
NASA Air Quality Applied Science Team Project
Physical Atmosphere Panel Meeting
April 25-26, 2012
Atlanta, GA
Physical Atmosphere Can Significantly Impact Atmospheric Chemistry and Resulting Air Quality
Most Importantly the Physical Atmosphere Can Impact Control Strategy Efficacy and Response
Temperature Mixing HeightsClouds Winds
Temperature
In most areas maximum temperature is most correlated with ozone.
Thermal decomposition of nitrogen species – (Sillman and Samson 1995)
Emissions – Biogenic and anthropogenic evaporative VOCs
Emissions – Soil NO and electric demand
Impact of Physical Atmosphere on SIP Control Strategies
Temperature – over prediction of temperature can bias ozone controls toward NOx controls as thermal decomposition of increases slope of ozone/NOy curves. Additionally, biogenic emissions will be overestimated.
Mixing Heights – Underestimate of mixing heights can cause an over-estimate of the sensitivity of controls. Emission reductions confined to a smaller volume cause a larger reduction in pollutants. A 30% error in mixing heights can produce 30% error in emission change impacts
MoistureSoil moisture impacts NOx emissions.
Atmospheric moisture can impact dry chemistry and wet chemistry.
Pollutant uptake by plants is directly related to photosynthesis and transpiration. Under-estimation of moisture and associated surface loss can overestimate the role of long range transport in local air pollution levels.
Climatology Drought
Winds
Winds can have a direct impact on precursor concentrations.
Light winds increase the accumulation of pollutants as air parcels have longer resident times over emission areas.
Underestimation of winds can increase control strategy sensitivity.
Wind Direction can also be critical for emission loading.
Clouds
Insolation
Temperature
Mixing Heights
Emissions
Photolysis J (NO2)
Deep Vertical Mixing
Boundary Layer Venting
Aqueous Chemistry
Aerosol Formation and Aging
Traditional view is that high pollution potential would occur near the center of a high pressure system.
A. Subsidence due to conservation of mass and potential vorticity would decrease mixing heights.
B. Light horizontal winds would reduce dilution
C. Clear skies increase photochemical potential
D. Temperatures are hot due to low ventilation and clear skies
HLight winds
Subsidence
DFW Daily Maxim um OzoneAugust 1999
0
20
40
60
80
100
120
140
160
180
8/1 8/6 8/11 8/16 8/21 8/26 8/31
Ozo
ne (
ppb)
Background Concentration Local Contribution
Figure 1.1 Plot of daily ozone values for DFW after Breitenbach 2004
Aug 4-5
Aug 14-17 Aug 25
High ozone events during 1999 were associated with stationary front
Beginning of sea breeze produces dead zones. Parcels in this area accumulate emissions and then are advected away with high precursor concentrations
c
c
2
c
c
RiRi,0
RiRi0,Ri
RiRi)Ri(mf
Km= Kh = l2s)Ri(mf
Quadratic Form
Depicted for Rc=0.2
Typical Boundary Layer Stable Parameterization
How well do models handle the stable boundary layer
Higher resolution boundary layer models generally have a closure scheme dependent on turbulent kinetic energy (TKE) equations or
Richardson Number analogues.
ndissipatioz
gK
z
VK
t
TKEhm
2)()(
shear generation buoyancy suppression
2)/(z
V
z
gRi
Ratio of buoyancy term and shear generation term is the Richardson Number
2)/(z
V
z
gRi
The problem with implementing these closures in large scale models is that the closure may be grid dependent
While the Richardson Number is dimensionless it is dependent on grid size
Thus as the vertical grid size increases Ri becomes larger
Modelers engineer around this by adding more mixing or using stability functions with more mixing (Louis profiles)
2)/(z
V
z
gRi
zV
gRi
2)(
0 0.1 0.2 0.3 0.4 0.5 0.60
0.2
0.4
0.6
0.8
1
1.2
England-McNiderDuynkerkeBeljaars-HoltslagLouis
F h(Ri)
Ri
Figure 2A: Stability functions used in the present paper. Ri is the gradient Richardson Number. See England and McNider 1995, Duynkerke 1991, Beljaars and Holtslag 1991 and Louis 1979. Duynkerke, Beljaars and Holtslag and Louis represent curve fits to the original parameterization. See also Van de Weil et al. 2002a
APPENDIX Goal-Minimize numerical diffusion
Figure 11: Differential heating for the case with clear air radiational forcing added radiative energy minus base case versus wind speed for different stability functions.
ECMWF/GABLS workshop 7-10 November 2011 (34)Conclusions on wind and momentum issues•Diurnal cycle of wind is attenuated in the ECMWF model by the stable diffusion scheme•The momentum boundary layer is too deep resulting in a too weak low level jet
Initial urban plume
The inertial oscillation distorts the plume but in the stable conditions little true diffusion occurs (i.e. concentrations are not changed)
However, the next morning PBL turbulence acts on the distorted plume so that the effective diffusion over night is very large resulting in a wide but diluted urban plume
McNider et al. 1993 . Atmos. Envir.
How Well Do Weather Models Predict CoBL Processes / Conditions?
Synoptic Diurnal Synoptic Diurnal
Observed wind spectra Model wind spectra