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Mexico City: Confluence of complex meteorology and air pollution - Photoacoustic measurements of aerosol light absorption and scattering at four sites in and near Mexico City. Lupita Paredes-Miranda & W. Patrick Arnott Atmospheric Sciences Program

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slide1
Mexico City: Confluence of complex meteorology and air pollution - Photoacoustic measurements of aerosol light absorption and scattering at four sites in and near Mexico City

Lupita Paredes-Miranda & W. Patrick Arnott

Atmospheric Sciences Program

University of Nevada Reno, Physics Department MS/220

AMS Student Chapter Presentation, Nov. 09, 2006

slide2
REFERENCES AND ACKNOLEDGEMENTS

Jerome Fast: PNNL

Jeffrey Gaffney & Nancy Marley: University of Arkansas

slide3
The MILAGRO field campaign was carried out in March 1-30, 2006 in Mexico City.

(fixed and mobile ground sites, aircraft, and satellites).

Understand the local and global radiative and cloud micro physical impacts of aerosol from a large city, Mexico City.

MCMA Mexico City Metropolitan Area (DOE, NSF, Mexico)

MAX-MEX Megacity Aerosol Experiment in Mexico City (DOE)

MIRAGE Megacities Impacts on Regional and Global Environment(NSF)

INTEX Intercontinental Chemical Transport Experiment(NASA, DOE, NSF)

slide4
LAT N 19 00

LONG W 99

Altitude 2240 m to 3700 m North to South

Area: 1 964 375Km²

slide5
~23,000,000 people in 2005

>4,000,000 Motor vehicles

About Mexico City…

measurement sites
T0: Instituto Mexicano del Petroleo, Distrito Federal, Northeast Mexico City.

T1: University of Tecamac, Tecamac, north of Mexico City.

T2: Rancho La Biznaga, Road to Pachuca Hidalgo, north of Mexico City.

T3: Paseo De Cortes, Amecameca, 12,500’ ASL on the saddle between volcanos Popocatepetl (17,883’ ASL) and Iztaccihuatl (17,338’ ASL).

MEASUREMENT SITES
slide7
Scale 25 miles between

IMP and U of Tecamac

Scale 65 miles between IMP and La Biznaga

slide9
1) slope flows

[Jauregui, Atmosfera, 1988]

2) gap wind

[Doran and Zhong, JAM, 2000]

3) density current

[Bossert, JAM,1997]

Local Meteorology

IMADA 1997 radar wind profiler and sounding sites

Cuautitlan

Teotihuacan

3700 m

2200 m

3500 m

Chalco

UNAM

4700 m

1300 m

biomass burning contributes to the regional air pollution

Biomass Burning Contributes to the Regional Air Pollution

MODIS Satellite Image 2 March 2004

marine stratus common

biomass burning sites (red)

effects of clouds
How do clouds affect aerosol properties over central Mexico and does the Mexico City plume significantly alter cloud evolution?
  • What is the fraction of boundary layer particulates vented into the free atmosphere through clouds?

Effects of Clouds

MODIS Satellite Image 31 March 2005

Mexico City

clouds often form over the mountains surrounding Mexico City during the dry season

air pollution in mexico city
~ 85% coming from fuel combustion

~ 15% dust

~ 44 x106 liters of burned fuel per year as follows:

25% industry, 11% housing, 9% power companies, and 55% in transportation

(REFERENCESecretaria del Medio Ambiente SMP:

Government Department for the study of the Environment)THIS TALK CONSIDERS…

Gaseous (NO2) and aerosol light absorption and scattering at sites T0, T1, T2 and T3, and interpretation.

Air Pollution in Mexico City
relatively clean afternoon at t0 imp located in northeast mc looking southwest
Relatively clean afternoon at T0, IMP (located in Northeast MC) looking southwest.
example of a morning when the mexico city plume goes south to popocatepetl volcano
Example of a morning when the Mexico City Plume Goes South to Popocatepetl volcano.

near forward scattering by particles sca = 30 degrees

r << r ~  r >> 

photoacoustic instrumentation at the sites
T0: IMP Mexico City

Absorption and Scattering by particles and gaseous compounds: 532 nm

T1: TECAMAC

Absorption and Scattering by particles: 870 nm

T2: LA BIZNAGA

Absorption by particles: 870 nm

T3: AMECAMECA Mountains

Absorption and Scattering by particles, 780nm

Photoacoustic instrumentation at the sites
photoacoustic instrument schematic for light absorption measurements
Basic principles:

Laser light is power modulated by the chopper.

Light absorbing aerosols convert light to heat - a sound wave is produced.

Microphone signal is a measure of the light absorption.

Light scattering aerosols don't generate heat.

Photoacoustic Instrument Schematic For Light Absorption Measurements

Acoustical Resonator

photoacoustic instrument details equation to obtain light absorption coefficient
Photoacoustic Instrument Details: Equation to Obtain Light Absorption Coefficient.

}

From the piezoelectric sound source

to site mexico city aerosol optics for 532 nm
12am

12am

06pm

06pm

12pm

12pm

21

26

11

16

21

26

11

16

06am

06am

00am

00am

TO Site Mexico City, Aerosol Optics for 532 nm

Aerosol Absorption: Note the day to day variability in the peak absorption, probably due to meteorology.

Aerosol Scattering: peaks later in the day than absorption, due to dust, OC, secondary organic aerosol, and inorganics.

1 day 1 hr 2 m s wind speed 4 48 mph arrow tail marks the day and the hour of the day

1 Day = 1 hr = 2 m/s wind speed = 4.48 mph Arrow tail marks the day and the hour of the day

slide23
WESTERLIES

EASTERLIES

slide24
12am

06pm

12pm

31

06

21

26

11

16

06am

00am

slide25
12am

06pm

12pm

06am

31

00am

06

21

26

11

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slide26
TO Site Mexico City Light Scattering for 532 nm (G. Paredes & P.Arnott) and 550 nm (J. Gaffney &N. Marley)

12am

12am

06pm

06pm

12pm

12pm

06am

06am

00am

00am

21

21

26

26

11

11

16

16

slide28
GASEOUS AND PARTICULATE ABSORPTION

12am

12am

06pm

06pm

12pm

12pm

06am

06am

00am

00am

11

15

09

13

21

11

15

09

13

21

Gaseous Absorption, 532 nm, mostly NO2(1/3 Mm-1 / ppb efficiency for absorption by NO2)

Note that gaseous absorption peaks 2 hours later in the day than particulate absorption. Peak particle absorption is 6x gaseous absorption peak.

average single scattering albedo scattering extinction
Average Single Scattering Albedo: Scattering/Extinction

Secondary

Organic

Aerosol

formation

(UV+VOCs)

Morning rush hour.

Large amounts of black carbon aerosol.

average single scattering albedo scattering extinction1
Average Single Scattering Albedo: Scattering/Extinction

Morning rush hour.

Large amounts of black carbon aerosol.

Regional Mixing

Increases

aerosol optics for 870 nm @ t1 30 minute average data
Aerosol Optics for 870 nm @ T1 30 minute average data

12am

12am

06pm

06pm

12pm

12pm

06am

06am

00am

00am

21

21

26

26

11

11

16

16

T1 Tecamac University typically has large amounts of windblown dust in the afternoon.

slide32
Cooling effect

Warming effect

Afternoon.

Well mixed atmosphere.

Regional SOA,

dust and local

emissions mix.

Morning rush hour.

Large amounts of black carbon aerosol.

slide33
Rancho La Biznaga, Mexico Rural Site: Absorption only, Long range plume transport from the south when level are higher.

12am

06pm

12pm

06am

00am

21

26

11

16

rural mountain site long range plume transport from the north when level are higher
Rural Mountain Site:, Long range plume transport from the north when level are higher.

12am

12am

06pm

06pm

12pm

12pm

06am

06am

06

31

31

06

11

16

21

26

00am

00am

21

26

11

16

06

slide35
A Tale of 2 Cities…

Vegas: Jan thru Feb

Daily variations small

Mexico City: March 15

Sunrise: 6:45 am

Sunset: 6:45 pm

las vegas nevada sits in a basin
Las Vegas Nevada sits in a basin

Site Location,

E Charleston

Typical Surface Wind Direction

Typical Wind Speed: 2 mph (daily average)

slide37
A Tale of 2 Cities…

Vegas: February 1, 2003

Sunrise: 6:42 am

Sunset: 5:07 pm

Lat N 35.2

Long W 115.2

City width 11 miles E-W

Wind Speed Ave 2.4 mph W-SW

Mexico City: March 15, 2006

Sunrise: 6:45 am

Sunset: 6:45 pm

Lat N 19.49

Long W 99.15

slide39
SUMMARY
  • Significant day to day variations of BC are observed due to meteorology in the Mexico City Basin.
  • Peak gaseous absorption is approx. 2 hrs later in the day than peak particle absorption. Peak 30-minute-average aerosol absorption in Mexico City was 180 Mm-1. Heating effects on BL dynamics are likely.
  • Daily single scattering albedos vary between 0.6 and 0.85 at 532 nm at the T0 site. Transportation dominates aerosol optics in the morning and secondary OC is important in the afternoon. Dust is also important at the T1 site.
slide40
Working on an instrument at Gloria’s house in Mexico City. Thanks for the help, “ayuda”. Thanks for your attention.
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