Transcript Global atmospheric changes and future impacts on regional

Global atmospheric changes and future impacts
on regional air quality
Will O3 produced elsewhere in the world affect local air quality?
How will a changing climate affect surface O3 concentrations?
Loretta J. Mickley
Harvard University
Number of people living in US counties violating
National Air Quality standards, 1999
Good O3 vs Bad O3
NOx = nitrogen oxide radicals
VOC = volatile organic carbon
How has tropospheric O3 increased in last 100 years?
Ozone measured on various mountaintops in Europe, 1870 to 1990
What could increase regional O3 in 21st century?
•
Increase of local emissions of O3 precursors (NOx, VOCs)
•
Transport of O3 or O3 precursors produced elsewhere
Can use model with observed winds to calculate current influence
•
Climate change effects on O3 loss and production rates
Need to use model that generates its own climate (GCM)
How does intercontinental transport of O3 enhance
local O3 surface concentrations today?
North America
Europe
Asia
GEOS-CHEM model, July
1997, Li et al 2002
How does N. American O3 affect O3 violations in Europe?
Number of exceedance days
for European standards
(55 ppb, 8 hour average)
Number of exceedance days
due to North American
sources
GEOS-CHEM model,
summer, Li et al 2002
Does Asian O3 enhance US surface O3 in summer?
Subsidence of Asian pollution
+ production aloft
Tropical
air
Maximum Asian
enhancements
(up to 14 ppb) occur at
intermediate ozone levels
(50-70 ppb)
Stagnation
Major concern if O3
standard decreases or
Asian O3 increases
Fiore et al. 2002
How important is methane to O3 and climate?
Methane = overlooked precursor of ozone, has long lifetime (8-10 years)
Cutting methane by 50% would:
decrease incidence of ozone > 80 ppb in surface air by more than 50%
decrease radiative forcing by both ozone and methane
Trends in methane
How might climate change affect O3 loss and production?
O2 + hn
Stratospheric ozone
Complex non-linear chemistry
?
Nitrogen oxides (NOx) hn Ozone (O ) hn, H2O Hydroxyl (OH)
3
CO, Hydrocarbons
?
Fires
?
Biosphere
O3 source with high NOx
O3 sink with low NOx
Human
activity
Ocean
physics
chemistry
biology
How might changing climate affect surface O3?
Temperature changes ? (not the whole story!)
Changes in circulation
frequency of stagnation?
stratospheric influx of ozone?
transport from other continents?
Lightning frequency?
Water vapor concentrations?
Emissions of VOCs from trees, grasses?
Sum of climate changes
more ozone? less ozone?
Chemistry, Aerosols, and Climate:
Tropospheric Unified Simulation (CACTUS)
Objective: to improve understanding of interactions between
atmospheric chemistry, aerosols, and climate
Approach: coupled chemistry-aerosol-climate
General Circulation Model (GCM)
CACTUS model
 emissions
 land use
 greenhouse gas
Atmospheric
chemistry
GISS GCM
Aerosol
microphysics
 climate
 chemistry
CACTUS model study of preindustrial O3
Monthly mean observations at
two sites in Europe
Two model attempts, with differing
natural emissions, but same climate
as present-day
Mickley et al. 2000
How will atmospheric motions change
in 2xCO2 climate?
Use SF6 to show how
atmospheric motions change
with warmer climate
• Stronger convective
transport
• Weaker interhemispheric
exchange
Rind et al., 2001
How can we calculate change in O3 due to climate?
1. 2000-2100: change well-mixed greenhouse gases year-by-year,
calculate  climate
2. 2000,2025,2050,etc: change emissions of O3 precursors, use
current climate, calculate  ozone
3. 2000,2025,2050,etc: recalculate  ozone using climate from step 1.
Diagnose  in ozone due to climate change. (Step 3- Step2)
Final thoughts
Transport could have a big effect in future if Asian emissions increase.
We need to learn how climate change may affect local ozone levels
Ozone in July 2100, worst case scenario