Section 9 Pollutant Lifecycles and Trends

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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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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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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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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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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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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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GLOBAL DISTRIBUTION OF CO

NOAA/CMDL surface air measurements

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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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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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0

50

100

150

200

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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

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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




ModerateModerate


Temperature below normalUnhealthy (4)Unhealthy (4)

2002

AQ

I

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-100

-80

-60

-40

-20

0

20

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AQ

I


ModerateModerate


Temperature below normalUnhealthy (2)Unhealthy (2)

2003

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Days above Air Pollution Index (API) in Shanghia, China from 2001-2005

0

1

2

3

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6

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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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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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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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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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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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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)


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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


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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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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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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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• GTT – Please provide examples showing the influence of weather, emissions, and chemistry

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• GTT – Please provide examples showing day of week influence on pollution

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• GTT - Show multi-day lifecycle of an episode

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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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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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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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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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0

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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)

Section 9 Pollutant Lifecycles and Trends

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