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 ArnottAtmospheric Sciences ProgramUniversity of Nevada Reno, Physics Department MS/220AMS Student Chapter Presentation, Nov. 09, 2006

REFERENCES AND ACKNOLEDGEMENTS

Jerome Fast: PNNL

Jeffrey Gaffney & Nancy Marley: University of Arkansas

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

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

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)

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

LAT N 19 00 LONG W 99Altitude 2240 m to 3700 m North to SouthArea: 1 964 375 Km²

• ~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).

Scale 25 miles between

IMP and U of Tecamac

Scale 65 miles between IMP and La Biznaga

Local Meteorology

Teotihuacan

Chalco

Cuautitlan

UNAM

1) slope flows[Jauregui, Atmosfera,

1988]

2) gap wind[Doran and Zhong, JAM,

2000]

4700 m

3) density current[Bossert, JAM,1997]

3700 m

3500 m

2200 m

1300 m

IMADA 1997 radar wind profiler and sounding sites

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? 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.

Sometimes transportation may pollute in a different way! Methane Makers…

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.

near forward scattering by particlessca = 30 degrees

r << r ~ r >>

Photoacoustic instrumentation at the sites

• T0: IMP Mexico CityAbsorption and Scattering by particles and gaseous compounds: 532 nm

• T1: TECAMACAbsorption and Scattering by particles: 870 nm

• T2: LA BIZNAGAAbsorption by particles: 870 nm

• T3: AMECAMECA Mountains Absorption and Scattering by particles, 780nm

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.

Light(532 nm)

Air Inletto pumpPhoto-detectorMicrophoneChopper

Acoustical Resonator

Schematic of the Photoacoustic instrument with scattering sensor

Sample InletSample Outlet

Input

Coupler

Output

Coupler

Piezoelectric

Transducer

Microphone and

Surrounds

RESONATOR

SECTION

COUPLING

SECTION

COUPLING

SECTION

Photodetector

C osine-

Weighted

Sensor.

Scattering

Measurement.

Fiber-coupled

to PMT.

LASER 1

LASER 2

LASER 3

Fiber 1

Fiber 3

Fiber 2

Culmination

Fiber

LASER

Photoacoustic Instrument Details: Equation to Obtain Light Absorption Coefficient.

Light Absorption in Dimensions of Inverse Distance = Babs

B

abs

=

Pm

P

L

Ares

γ − 1

π2

f

0

Q

,

f0=ResonanceFrequency.=Q ResonatorQualityFacto .r

Pm=PeakAcousticPressureatf0.= Ratio of Isobaric andIsochoricSpecificHeatsForA .ir PL=PeakLaserBeamPower atf0.

=Q resonatorqualityf .actorAres= Resonator CrossSectionalA .rea

}From the piezoelectric sound source

γ

Inlet System at T0

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.

00am

06am

12pm

06pm

12am

11

16

21

26

00am

06am

12pm

06pm

12am

11

21

16

26

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

EASTERLIES

WESTERLIES

00am

06am

12pm

06pm

12am

16 21 26 31 06 11

00am

06am

12pm

06pm

12am

11 16 21 26 06 31

00am

06am

12pm

06pm

12am

00am

06am

12pm

06pm

12am

11

16

21

26

11

16

21

26

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

Particles, Electron Microscope, by R. Chakrabarty and C. Mazzoleni

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.

GASEOUS AND PARTICULATE ABSORPTION

00am

06am

12pm

06pm

12am

00am

06am

12pm

06pm

12am

09

11 13

15 21 09

11

13

15

21

Average Single Scattering Albedo: Scattering/Extinction

Morning rush hour.

Large amounts of black carbon

aerosol.

SecondaryOrganicAerosolformation (UV+VOCs)

Average Single Scattering Albedo: Scattering/Extinction

Morning rush hour.

Large amounts of black carbon

aerosol.

Regional MixingIncreases

Aerosol Optics for 870 nm @ T1 30 minute average data

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

00am

06am

12pm

06pm

12am

11

16

21

26

11

16

21

26

00am

06am

12pm

06pm

12am

Cooling effectWarming effect

Morning rush hour.Large amounts of black carbon aerosol.

Afternoon.Well mixed atmosphere.

Regional SOA, dust and local emissions mix.

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

11

16

21

26

00am

06am

12pm

06pm

12am

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

06

11

16

21

26

06 31

00am

06am

12pm

06pm

12am

3100am

06am

12pm

06pm

12am

2621161106

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

Site Location,

E Charleston

Typical Surface Wind Direction

Typical Wind Speed: 2 mph (daily average)

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

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.

Working on an instrument at Gloria’s house in Mexico City. Thanks for the help, “ayuda”. Thanks for your attention.