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Section 9Pollutant Lifecycles and Trends
Definitions and Importance
Multi-year (Long-term) Trends
Seasonal Trends
Short-term Changes
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THE ATMOSPHERE: OXIDIZING MEDIUM IN GLOBAL BIOGEOCHEMICAL CYCLES
EARTHSURFACE
Emission
Reduced gasOxidized gas/aerosol
Oxidation
Uptake
Reduction
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Section 9 – Pollutant Lifecycles and Trends3
Definitions and Importance
• Definitions– Trends are longer-term (multi-year) changes in air pollution caused by
population and emissions changes– Lifecycles are daily and episodic changes in pollution levels– Episodes are several day events when air quality concentrations are
high
• Importance to forecasting– Determining how emissions changes affect air quality– Knowing which pollutants occur in each season– Understanding “typical” day-to-day changes
• Three time periods– Long-term trends– Seasonal trends– Short-term lifecycles
• Day/night (diurnal)• Day of week• Multi-day
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Multi-year Trends
• Multi-year trends – Five or more years
• Affected by– Emissions changes
• As emissions controls occur, pollutant levels typically decrease
• Similar weather conditions may not produce the same pollutant concentrations
– Year-to-year weather changes• Multi-year climate changes
• For example, above normal temperatures typically result in above normal ozone concentrations
– Monitor environment changes (location, environment)• If monitors move or the environment around monitors changes, the resulting air
quality conditions will be affected
– Metric used to evaluate trends can affect trend results• Maximum (peak) concentration
• 90th percentile
• 4th highest value
• Days above a threshold
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Section 9 – Pollutant Lifecycles and Trends5
Ozone concentrations are therefore likely to increase greatly in mid-latitudes in the future(GEOS-CHEM runs by Arlene Fiore, Harvard U.)
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Section 9 – Pollutant Lifecycles and Trends6
OZONE TREND AT EUROPEAN MOUNTAIN SITES, 1870OZONE TREND AT EUROPEAN MOUNTAIN SITES, 1870--19901990
Preindustrialozone models
}
Marenco et al. [1994]
Increase is important from pollution and climate perspectives
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Section 9 – Pollutant Lifecycles and Trends7
Multi-year Trends Example (1 of 3)
http://www.aqmd.gov/smog/o3trend.html
Long-term ozone trends in Los Angeles, California, USA
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Section 9 – Pollutant Lifecycles and Trends8
Multi-year Trends Example (2 of 3)
Number of days with daily maximum 1-hour O3 > 0.10 ppm at any one site in each capital city of Australia, 1991–2001
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Section 9 – Pollutant Lifecycles and Trends9
Seasonal Trends
• Affected by– Season (temperature, precipitation, clouds)
• Unusual weather conditions may affect severity of episodes• For example, above normal temperatures typically result in above
normal ozone concentrations
– Emissions changes (substantial)• Reformulated fuel• Changes in industrial emissions• Other
• Useful to understand typical season for each air pollutant– Determines forecasting season
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Section 9 – Pollutant Lifecycles and Trends10
GLOBAL DISTRIBUTION OF CO
NOAA/CMDL surface air measurements
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Section 9 – Pollutant Lifecycles and Trends11
O3 at the surface
• Surface sites in industrialized regions show an even more pronounced summer-time peak
Seasonal cycle of O3 concentrations at the surface for different rural locations in the United States.
From Logan, J. Geophys. Res., 16115-16149, 1999.
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Section 9 – Pollutant Lifecycles and Trends12
Seasonal Trends Example (1 of 5)
Compare ozone vs. temperature departure from normal• Columbus, Ohio, USA• Daily 8-hr ozone concentration (AQI)• Temperature departure
– Daily maximum temperature – daily normal temperature
2001 2002 2003
Number of high ozone days
Unhealthy for Sensitive Groups on the AQI scale
9 28 6
Number of days with above normal temperature
64 93 40
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Section 9 – Pollutant Lifecycles and Trends13
Seasonal Trends Example (2 of 5)
0
50
100
150
200
250
300
5/1
5/8
5/15
5/22
5/29 6/
56/
126/
196/
26 7/3
7/10
7/17
7/24
7/31 8/
78/
148/
218/
28 9/4
-100
-80
-60
-40
-20
0
20
40
Temperature departure from normal vs. maximum ozone AQI
AQ
I
Temperature above normal (64)
Temperature below normal
Unhealthy for SG (9)Unhealthy for SG (9)
ModerateModerate
2001
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0
50
100
150
200
250
300
5/1
5/8
5/15
5/22
5/29 6/
56/
126/
196/
26 7/3
7/10
7/17
7/24
7/31 8/
78/
148/
218/
28 9/4
9/11
9/18
9/25
-100
-80
-60
-40
-20
0
20
40
Seasonal Trends Example (3 of 5)
Temperature departure from normal vs. maximum ozone AQI
Unhealthy for SG (24)Unhealthy for SG (24)
ModerateModerate
Temperature above normal (93)
Temperature below normalUnhealthy (4)Unhealthy (4)
2002
AQ
I
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Section 9 – Pollutant Lifecycles and Trends15
Seasonal Trends Example (4 of 5)
Temperature departure from normal vs. maximum ozone AQI
0
50
100
150
200
250
300
-100
-80
-60
-40
-20
0
20
40
AQ
I
Unhealthy for SG (4)Unhealthy for SG (4)
ModerateModerate
Temperature above normal (40)
Temperature below normalUnhealthy (2)Unhealthy (2)
2003
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Seasonal Trends Example (5 of 5)
Days above Air Pollution Index (API) in Shanghia, China from 2001-2005
0
1
2
3
4
5
6
7
8
9
10
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Ave
rag
e A
nn
ual
Day
s A
bo
ve 1
00 A
PI
SO2
NO2
PM10
Days above Air Pollution Index (API) in Shanghai, China, from 2001-2005
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Section 9 – Pollutant Lifecycles and Trends17
Short-Term Lifecycles
• Largely controlled by weather conditions and emissions events that are predicable
• Affected by – Weather conditions
• Sunlight• Winds• Dispersion• Other factors
– Large emissions changes• Fires• Non-routine emissions events (holidays, etc.)• Day-of-week emissions changes
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Section 9 – Pollutant Lifecycles and Trends18
0
20
40
60
80
100
120O
zo
ne
Co
nc
en
tra
tio
n (
pp
b) Net Ozone Net
Production Peak DestructionPrecursor
Accumulation
Emissions Dispersion Vertical mixing Sunlight TransportRemoval
Short-Term Changes – Example (1 of 9)
Hour (LT)
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Section 9 – Pollutant Lifecycles and Trends19
Short-Term Changes – Example (2 of 9)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour
No
rmal
ized
tra
ffic
act
ivit
y, m
ixin
g h
eig
ht,
or
sola
r ra
dia
tio
n
Traffic Activity
Mixing Height
Solar Radiation
Key diurnal factors
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Short-Term Changes – Example (3 of 9)
Diurnal Pattern Categories
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour (LT)
Temp
Solar Radiation
Wind Speed
Mixing Depth
Secondary Production (Ozone)
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Short-Term Changes – Example (5 of 9)
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour (LT)
Temp
Solar Radiation
Wind Speed
Mixing Depth
Mobile Source (CO)
Diurnal Pattern Categories
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Short-Term Changes – Example (6 of 9)
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour (LT)
Temp
Solar Radiation
Wind Speed
Mixing Depth
PM2.5
Diurnal Pattern Categories
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Multi-day time series for model predictions at surface sites.
AIRMAP Site: Thomson Farm
0
20
40
60
80
100
120
140
160
190 200 210 220 230
julian day
O3
(ppb
v) obs
NEI99
NEI01
AIRMAP Site: Thomson Farm. CO (ppbv)
0
100
200
300
400
500
600
700
800
900
190 200 210 220 230
julian day
CO
(pp
bv)
obs
NEI99
NEI01
AIRMAP Site: Thomson Farm. NOy (ppbv)
0
5
10
15
20
25
30
35
40
190 200 210 220 230
julian day
NO
y (p
pbv)
obs
NEI99
NEI01
Figure. Comparison of model performance in surface sites, NEI 1999 and NEI 2001
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Section 9 – Pollutant Lifecycles and Trends24
Lifecycles – Multi-day
Combined ozone and PM2.5
0
20
40
60
80
100
120
140
21-Jun 22-Jun 23-Jun 24-Jun 25-Jun 26-Jun 27-Jun 28-Jun
Ozo
ne
Co
nc
en
tra
tio
n (
pp
b)
0
10
20
30
40
50
60
70
80
PM
2.5
Co
nc
en
tra
tio
n (
ug
/m3
)
Ozone
PM2.5
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PM 2.5 Variation in Beijing
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Temperature
Dewpoint
Wind Speed
PM 2.5 variation with:
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Build-up of regional PM 2.5
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Sulfur-to-Aluminum Ratio
Ratio of PM2.5 to PM10
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Section 9 – Pollutant Lifecycles and Trends29
Summary
Trends and lifecycle of pollution• Long-term – Controlled by changes in emissions and
climate• Seasonal – Controlled by annual and seasonal weather
patterns• Short-term – Controlled by weather and non-routine
emissions events
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Short-Term Changes – Example (7 of 9)
• GTT – Please provide examples showing the influence of weather, emissions, and chemistry
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Short-Term Changes – Example (8 of 9)
• GTT – Please provide examples showing day of week influence on pollution
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Short-Term Changes – Example (9 of 9)
• GTT - Show multi-day lifecycle of an episode
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Multi-year Trends Example (3 of 3)
Ozone trends with and without adjusting for meteorology
The top left panel shows the raw ozone season values while the top right panel shows the seasonal values adjusted for meteorology. Values on the y-axis are on a log scale with the mean removed. The bottom two panels are just smooth splines fit to the data in the top two panels. The plots also include +/- twice the standard error of prediction. (Courtesy: Bill Cox, U.S. EPA)
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Section 9 – Pollutant Lifecycles and Trends34
PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-
RANGE TRANSPORT OF NOx
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Winds Clouds, fog Winds Temperature
Temperature Temperature Precipitation Relative humiditySolar radiation Relative humidity WindsVertical mixing Solar radiation
condensation andcoagulation
photochemical productioncloud/fog processes
gases condense onto particles
cloud/fog processes Measurement Issues
• Inlet cut points• Vaporization of
nitrate, H2O, VOCs• Adsorption of VOCs• Absorption of H2O
transport
sedimentation(dry deposition)
wet deposition
Mechanical• Sea salt• Dust
Combustion• Motor vehicles• Industrial• Fires
Other gaseous• Biogenic• Anthropogenic
Particles• NaCl• Crustal
Particles• Soot• Metals• OC
Gases• NOx
• SO2
• VOCs• NH3
Gases• VOCs• NH3
• NOx
SourcesSample
CollectionPM Transport/LossPM
FormationEmissionsChemical Processes
Meteorological Processes
Particulate Matter Chemistry (4 of 4)
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Winds Clouds, fog Winds Temperature
Temperature Temperature Precipitation Relative humiditySolar radiation Relative humidity WindsVertical mixing Solar radiation
condensation andcoagulation
photochemical productioncloud/fog processes
gases condense onto particles
cloud/fog processes Measurement Issues
• Inlet cut points• Vaporization of
nitrate, H2O, VOCs• Adsorption of VOCs• Absorption of H2O
transport
sedimentation(dry deposition)
wet deposition
Mechanical• Sea salt• Dust
Combustion• Motor vehicles• Industrial• Fires
Other gaseous• Biogenic• Anthropogenic
Particles• NaCl• Crustal
Particles• Soot• Metals• OC
Gases• NOx
• SO2
• VOCs• NH3
Gases• VOCs• NH3
• NOx
SourcesSample
CollectionPM Transport/LossPM
FormationEmissionsChemical Processes
Meteorological Processes
Particulate Matter Chemistry (4 of 4)
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Phenomena Emissions PM Formation PM Transport/Loss
Aloft Pressure Pattern
No direct impact. No direct impact. Ridges tend to produce conditions conducive for accumulation of PM2.5.
Troughs tend to produce conditions conducive for dispersion and removal of PM and ozone.In mountain-valley regions, strong wintertime inversions and high PM2.5 levels may not be
altered by weak troughs. High PM2.5 concentrations often occur during the approach of a trough from the west.
Winds and Transport
No direct impact. In general, stronger winds disperse pollutants, resulting in a less ideal mixture of pollutants for chemical reactions that produce PM2.5.
Strong surface winds tend to disperse PM2.5 regardless of season.
Strong winds can create dust which can increase PM2.5 concentrations.
Temperature Inversions
No direct impact. Inversions reduce vertical mixing and therefore increase chemical concentrations of precursors. Higher concentrations of precursors can produce faster, more efficient chemical reactions that produce PM2.5.
A strong inversion acts to limit vertical mixing allowing for the accumulation of PM2.5.
Rain No direct impact. Rain can remove precursors of PM2.5. Rain can remove PM2.5.
Moisture No direct impact. Moisture acts to increase the production of secondary PM2.5
including sulfates and nitrates.
No direct impact.
Temperature Warm temperatures are associated with increased evaporative, biogenic, and power plant emissions, which act to increase PM2.5. Cold temperatures can also
indirectly influence PM2.5
concentrations (i.e., home heating on winter nights).
Photochemical reaction rates increase with temperature.
Although warm surface temperatures are generally associated with poor air quality conditions, very warm temperatures can increase vertical mixing and dispersion of pollutants.Warm temperatures may volatize Nitrates from a solid to a gas.Very cold surface temperatures during the winter may produce strong surface-based inversions that confine pollutants to a shallow layer.
Clouds/Fog No direct impact. Water droplets can enhance the formation of secondary PM2.5. Clouds
can limit photochemistry, which limits photochemical production.
Convective clouds are an indication of strong vertical mixing, which disperses pollutants.
Season Forest fires, wood burning, agriculture burning, field tilling, windblown dust, road dust, and construction vary by season.
The sun angle changes with season, which changes the amount of solar radiation available for photochemistry.
No direct impact.
Particulate Matter MeteorologyHow weather affects PM emissions, formation, and transport
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ORIGIN OF THE ATMOSPHERIC AEROSOL
Soil dustSea salt
Aerosol: dispersed condensed matter suspended in a gasSize range: 0.001 m (molecular cluster) to 100 m (small raindrop)
Environmental importance: health (respiration), visibility, radiative balance,cloud formation, heterogeneous reactions, delivery of nutrients…
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PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-
RANGE TRANSPORT OF NOx
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Lifetimes of ROGs Against Chemical Loss in Urban Air
Table 4.3
ROG Species Phot. OH HO2 O NO3 O3 n-Butane --- 22 h 1000 y 18 y 29 d 650 ytrans-2-butene --- 52 m 4 y 6.3 d 4 m 17 mAcetylene --- 3 d --- 2.5 y --- 200 dFormaldehyde 7 h 6 h 1.8 h 2.5 y 2 d 3200 yAcetone 23 d 9.6 d --- --- --- ---Ethanol --- 19 h --- --- --- ---Toluene --- 9 h --- 6 y 33 d 200 dIsoprene --- 34 m --- 4 d 5 m 4.6 h
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Impacts of NOx emission
• by mass, most NOx is emitted at the surface
• chemical impacts of NOx very non-linear
– limited impact in the continental PBL• high OH and high NO2/NO ratio near surface result
in a short photo-chemical lifetime
• NOx concentrations are already substantial
– per molecule, impact of NOx much greater in free troposphere
• venting to the free troposphere important• emissions that occur in free troposphere
– aircraft, lightning
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Global tropospheric ozone
• Remote northern stations– spring-time maximum
• nearer to industrial emissions– broader maximum stretching through summer
Seasonal cycle of O3 concentrations at different pressure levels, derived from ozonesonde data at eight different stations in the northern hemisphere. From Logan, J. Geophys. Res., 16115-16149, 1999.
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Global distribution
• constructed from surface observations, ozonesondes and a bit of intuition– note very low concentrations over tropical Pacific ocean
Spatial distribution of climatological O3 concentrations at 1000hPa.
From Logan, J. Geophys. Res., 16115-16149, 1999.
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Section 9 – Pollutant Lifecycles and Trends44
Measurements from satellite
• Data from asd-www.larc.nasa.gov/TOR/data.html• See Fishman et al., Atmos. Chem. Phys., 3, 893-907, 2003.
– Tropospheric residual method• total column (from TOMS) - stratospheric column (SBUV)
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Midwest
NY-MA-MD
TX-NM
Southeast
Ohio etc
California
Canada
2km wind field
A strong outflow event will appear from Saturday to Sunday
Mission Overview
July 1 to 25 Model CO
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Aerosols in the East Asia Environment Have a Profound Impact on Resulting Secondary Pollution Formation Through Radiative
Feedbacks
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Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS-CHEM model results for 1997 (contours).
GEOS-CHEM tropospheric ozone columns for July 1997.
GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE
Li et al. [2001]
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Short-Term Changes – Example (4 of 9)
Diurnal Pattern Categories
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour (LT)
Temp
Solar Radiation
Wind Speed
Mixing Depth
Ozone (Background)