Post on 30-Dec-2015
OMI HCHO columnsJan 2006 Jul 2006
Policy-relevant background (PRB) ozone calculations for the EPA ISA and REA
Zhang, L., D.J. Jacob, N.V. Smith-Downey, D.A. Wood, D. Blewitt, C.C. Carouge, A. van Donkelaar, D.B.A. Jones, L.T. Murray, and Y. Wang, Improved estimate of the policy-relevant background ozone in the United States using the GEOS-Chem global model with 1/2ox2/3o horizontal resolution over North America, Atmos. Environ., 45, 6769-6776, doi:10.1016/j.atmosenv.2011.07.054, 2011
Lin Zhang and Daniel Jacob
Air quality management partner: Joe Pinto (EPA/NCEA)
GEOS-Chem nested simulation for North America
2ox2.5o
0.5o x0.67o
• 0.5o x0.67o resolution for North America, 2o x2.5o global, 48 vertical layers
• Driven by NASA GEOS-5 assimilated meteorological data• Detailed mechanistic representation of ozone-NOx -VOC-aerosol chemistry• 2006 anthropogenic emissions: NEI05 for US, CAC for Canada, BRAVO (scaled)
for Mexico, EMEP for Europe, Streets for East Asia, EDGAR (scaled) for rest of world
• Natural sources: lightning (OTD/LIS), fires (GFED2 monthly), soils (Yienger), stratosphere (Linoz)
• 2006-2008 3-year simulation; focus on 2006 for evaluation
Color scale Indicates topography (surface pressure)
Ozone statistics for the US (CASTNet sites)
+ > 1.5 km
PRB: 27 ± 8
40 ± 7
Natural: 18 ± 6
27 ± 6
Frequency distribution of MDA8 ozonefor March-August 2006
• GEOS-Chem is overall unbiased• PRB is 4 ppb higher than in
previous GEOS-Chem versions• Model shows little interannual
variability for 2006-2008, but neither do observations
Obs: 50 ± 13Model: 52 ± 12
58 ± 957 ± 10
Zhang et al. [2011]
Model “4th highest” MDA8 ozone in 2006
Background may limit or confuse ability of West to achieve a 60 ppb NAAQS; no such issue in East
Annual 4th highest ozone
PRB for annual 4th highest ozone 4th highest PRB value
Zhang et al. [2011]
Model PRB statistics vs. observed ozone in Intermountain West
Comparison of daily MDA8 ozone concentrations for the ensemble of elevated sites (>1.5 km; 11 sites) in Intermountain West for spring and summer 2006
Model underestimates high extrema in spring (> 75 ppbv) - stratosphere Correlation with measurements is poor in summer – lightning, wildfires
1:1 line
max
min
75th50th25th
r = 0.57 r = 0.33
Lin Zhang, Harvard
Model underestimate of stratospheric intrusions in spring
Sample stratospheric intrusion at Pinedale (WY) : model captures timing but not magnitude.
Obs.
model
PRB
Observed vs. simulated MDA8 ozone in spring 2006 at the 11 elevated CASTNet sites, colored by model stratospheric ozone concentration.
Model has correct STE and vertical transport; we attribute problem to the general difficulty of Eulerian models in resolving fine structures.
Lin Zhang, Harvard
observations
stratosphere
Ozone enhancement from lightning in Intermountain West
Model lightning increases ozone concentrations by 7-19 ppbv in summer, comparable to enhancements from US anthropogenic emissions.
This lightning influence in the model is biased high, even though lightning location is constrained by OTD/LIS satellite observations;
focus future model improvement on NOx yield per lightning flash, vertical distribution
Lin Zhang, Harvard
model
PRB
observations
lightning
Sensitivity of model ozoneto wildfire emission inventory
fire reportsmonthly
Maximum fire enhancements of MDA8 ozoneIn GEOS-Chem – August 2006
• Model is highly sensitive to choice of inventory, spatial and temporal resolution
• Influence of fires is mainly limited to fire region; little influence at CASTNet sites in 2006
• Need to examine other years, MOPITT and AIRS CO data for fires
Lin Zhang, Harvard
Observed interannual correlation of ozone with wildfiresmay reflect common variation with temperature
Ozone correlation with T at elevated CASTNet sites (summer 2006) Correlation of T with PBL depth
Subsidence of background air appears to be a major factor driving variability of ozone in the intermountain West
Lin Zhang, Harvard
ObservationsModel
GEOS-5
New IP: Nitrogen Deposition to US National Parks
Motivation:• N deposition at some National
Parks has reached critical load: changes may not be reversible
• Nitrogen wet deposition at Rocky Mountain NP is twice the critical load of 1.5 kg N ha-1 a-1
• Need to understand where the N is coming from and in what form
Approach:• Simulate N deposition with nested
GEOS-Chem model, evaluate with surface data and OMI NO2
• Initial focus on source attribution for RMNP
Outcome:• Contribute to RMNP Nitrogen
Deposition Reduction Plan
Raluca Ellis and Daniel Jacob (Harvard)Air quality management partner: Bret Schichtel (NPS)
NH4+
NO3-
1985-2002 trend in wet deposition fluxes(Lehmann et al., 2005)