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Interactions Between Air - PowerPoint Presentation

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Interactions Between Air - PPT Presentation

Quality and Climate Change over the Eastern United States An Investigation of Climate Change in Our Own Backyard Loretta J Mickley Harvard University Wildfires in Quebec the same day ID: 758093

climate ozone nox trend ozone climate trend nox vocs cold warming fronts change surface particles 1980 models ppb episodes observed pollution summer

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Slide1

Interactions Between Air Quality and Climate Change over the Eastern United States: An Investigation of Climate Change in Our Own Backyard

Loretta J. MickleyHarvard University

Wildfires in

Quebec the same day.

Haze over Boston on

May 31, 2010

Daniel J.

Jacob, Eric M.

Leibensperger, Amos P.K.A. Tai, Shiliang Wu

EPA Science Forum, March 14, 2012

1Slide2

2

Our work focuses on interactions of short-lived gases and particles in the atmosphere and climate change.Lifetimes in atmospheric chemistry

Centuries: SF6, some CFCs Decades:

many greenhouse gases: CO2, N2O, . . . 9-10 years: CH

4 (methane, precursor to ozone and greenhouse gas)Days-weeks: O3 (ozone), particulate matter (PM)Seconds: OH, NO

Pollution over Hong Kong

Air pollution over Hong Kong reached dangerous levels one of every eight days in 2009Slide3

Air pollution in the United States: Ozone

and fine particulate matter (PM2.5) are the two main pollutants

75 ppb (8-h average)

15

m

g m-3

(1-y av.)

Ozone

PM

2.5

Counties violating the EPA standards

3

Millions of people living in areas in violation of the standards.Slide4

The greenhouse effect keeps the Earth warm.

IPCC, 2007

Greenhouse Effect

Radiation from the earth’s surface is absorbed and re-emitted by clouds and greenhouse gases: CO

2. . .This process warms the earth.

CO

2

CO2

CO24

Change in CO

2

since mid-1800s: 280 ppm to 390 ppm.Slide5

Observed trends in surface temperature, 1880-2011.

NASA

Goddard Institute for Space Studies

Global mean temperature increase is ~0.5

oC since 1950s.

Boston/ Logan Airport

Over Boston, we see lots of year-to-year variability, but a significant trend towards warming.

Record annual mean temperature

5Slide6

Climate models show that observed global warming trends cannot be explained without human influence.

IPCC, 2007

Models with human activity.

Models with just natural processes

Observed trend

Observed trend

6Slide7

7

Basic working of climate modelsAll climate models depend on

basic physics to describe motions and thermodynamics of the atmosphere:

E.g., vertical structure of pressure is described by hydrostatic equation

Climate models also depend on

parameterizations

for many processes.

E.g., microphysics of cloud droplet formation, vegetation processes.

Tilt of earth, geography, greenhouse gas content

Weather + Climate

Input

Physics + Parameterized processes

Climate model

OutputSlide8

Simulations of future climate depend on the path of socio-economic development.

Different scenarios follow different socio-economic paths for developed and developing countries

.

IPCC 2007

Global mean surface temperature anomalies

A2 = heavy fossil fuel

B1 = alternative fuels

A1B = mix of fossil + alternative fuels

8Slide9

What do climate models

predict for future (2100) climate?Christensen et al., 2007

Annual mean Winter Summer

Annual mean Winter Summer

Temperature increases everywhere,

especially at high latitudes.

Precipitation will likely increase over high latitudes but decrease over low latitudes.

In between, the trend is not clear!

Much uncertainty in future precipitation.

Precipitation changes are more complicated.

9Slide10

How do particles affect regional climate?10Slide11

Particles affect solar radiation directly…and also indirectly by modifying cloud properties.

Pollution off U.S. east coast

Black carbon

California fire plumes

Aircraft contrails and cirrus over Europe

Light-colored particles reflect sunlight and cool the earth’s surface.

cooler

11Slide12

Comparison to observed sulfate concentrations shows good agreement.

Sequence shows increasing sulfate from 1950-1980, followed by a decline in recent years. Most of aerosol has already cleared by 2010.

1950

1960

1970

1980

1990

2001

Leibensperger

et al., 2011

Calculated trend in surface sulfate concentrations, 1950- 2001.

Clearing trend

in

particles

over United States

since 1980s suggests possible recent warming.

12Slide13

Observed US surface temperature trendGISTEMP [2010]

Is the U.S. “warming hole” a signature of cooling due to particles?

Change in temperatures over 60 year period, 1930-1990

No trend between 1930 and 1980

Warming trend after 1980

Contiguous US

o

C

13Slide14

We can examine the influence of particles on regional climate using a climate model. Most of the warming from reducing particle sources has already been realized.

Observations

Model without US particles

Standard model

US manmade particles can explain the “warming hole.”

Warming since 1990s can be attributed to reductions in particle sources.

Leibensperger

et al., 2012

Eastern US

14Slide15

How does climate change affect smog episodes?15Slide16

EPA

Roles of ozone (O3) in the atmosphere.

O

2

O3

16Slide17

Weather plays a large role in ozone air quality.

1988, hottest on record

Days

Number of summer days with ozone

exceedances

, mean over sites in Northeast

Lin et al., 2001

A very hot summer can mean more ozone

exceedances

, even if emissions of ozone precursors are declining.

17Slide18

In the Northeast, cold fronts sweep out pollution.

During heat wave:

Clear skiesFaster chemical reactionsGreater biogenic emissions

Little ventilation of pollutants

Leibensperger et al., 2008

Can climate change affect the frequency of cold fronts?

Fewer cold fronts could mean more persistent smog episodes.

18Slide19

The number of cold fronts coming through the Northeast has already showed a signal of decline.

Trend in

low-pressure systems and associated cold fronts is linked to rapid warming at high latitudes.

What does this trend mean for ozone pollution in US?Emissions of ozone precursors have declined during this period.

Mickley et al., 2004;

Leibensperger

et al., 2008

Trend

in summer low-pressure systems in S. Canada

0.14

/year

0.16

/year

observations

with increasing GHGs

with constant GHGs

model

model

19Slide20

Trend in emissions and trend in cold fronts have competing effects on surface ozone.Emissions

Ozone Episodes

Cold fronts per summer

Ozone Episodes

More heat waves, less ventilation, more persistent smog.

Smog over Baltimore in 2002.

20Slide21

Observed trends of ozone pollution and cold fronts in Northeast US

Ozone exceedance days in Northeast dropped from 30 in 1980 to 10 in 2006, but would have dropped to ≈ zero in the absence of cold-front trend.

Leibensperger

et al. [2008]

Number of ozone

episode days (O

3> 80 ppb) + Number of cold fronts, 1980-2006

Cold fronts each summer

Ozone episodes

Ozone episodes, constant climate

21Slide22

Change in

max daily 8-hour average JJA surface ozone in 2050s, relative to present-day.

Most models agree that surface ozone will increase over the

Northeast in a warming climate.

Climate penalty for air quality

:

Harvard model shows

3-7 ppb

increase in surface ozone in Midwest US in 2050s climate.

During heatwaves

, increases in ozone reach 10 ppb in future climate.

ppb

Wu et al., 2008

22Slide23

Take home messages:Reductions in particles (PM2.5) over the Eastern US has likely contributed to rapid warming

in recent years.Smog episodes in the East are sensitive to many meteorological variables, especially the frequency of cold fronts. The climate penalty:

climate change will likely worsen ozone air quality over the East.

Contiguous US

o C

Rapid warming after 1980

Acknowledgments:

23Slide24

24Slide25

25Slide26

26

O

3

O

2

h

n

O

3

Deposition

STRATOSPHERE

TROPOSPHERE

8-18 km

Lifecycle of tropospheric ozone:

production is via

oxidation of CO, VOCs, and methane in the presence of NOx.

NOx

Nonmethane volatile organic compounds (VOCs)

NOx = NO + NO

2

Human activity

Fires

Biosphere

emissions

Many processes affected by climate

NOx

NOx

NOx

VOCs

NOx

NOx

VOCs

VOCs

VOCs

VOCs

CO

CO

CH

4

CH

4

Soup of chemical reactions

Ozone is produced in the atmosphere in sunlight.

26Slide27

27

Life cycle of particulate matter (PM, aerosols)

nucleation

coagulation

condensation

wildfires

combustion

soil dust

sea salt

.

.

.

.

.

.

cycling

ultra-fine

(<0.01

m

m)

fine

(0.01-1

m

m)

cloud

(1-100

m

m)

combustion

volcanoes

agriculture

biosphere

coarse

(1-10

m

m)

scavenging

precursor gases

Climate change affects many processes, including gas-particle partitioning.

Soup of chemical reactions

NOx

NOx

NOx

NOx

NOx

VOCs

VOCs

VOCs

VOCs

VOCs

SO

2

NH

3

SO

2Slide28

Current standard (75 ppb)

EPA-recommended range for revision of standard (60-70 ppb)

Exceedances

of the ozone air quality standard

28