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

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 LONG W 99 Altitude 2240 m to 3700 m North to South Area: 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 commonbiomass 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 x10 6 liters of burned fuel per year as follows: 25% industry, 11% housing, 9% power companies, and 55% in transportation ( REFERENCE Secretaria del Medio Ambiente SMP: Government Department for the study of the Environment) THIS TALK CONSIDERS… Gaseous (NO 2 ) 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 particles  sca = 30 degrees 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 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. Acoustical Resonator

Schematic of the Photoacoustic instrument with scattering sensor LASER

Photoacoustic Instrument Details: Equation to Obtain Light Absorption Coefficient. } From the piezoelectric sound source 

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 am 06am 12pm 06pm 12am

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

00am 06am 12pm 06pm 12am

00am 06am 12pm 06pm 12am 00am 06am 12pm 06pm 12am 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 NO 2 (1/3 Mm -1 / ppb efficiency for absorption by NO 2 ) 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

Average Single Scattering Albedo: Scattering/Extinction Morning rush hour. Large amounts of black carbon aerosol. Secondary Organic Aerosol formation (UV+VOCs)

Average Single Scattering Albedo: Scattering/Extinction Morning rush hour. Large amounts of black carbon aerosol. Regional Mixing Increases

Aerosol Optics for 870 T1 30 minute average data T1 Tecamac University typically has large amounts of windblown dust in the afternoon. 00am 06am 12pm 06pm 12am am 06am 12pm 06pm 12am

Cooling effect Warming 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 am 06am 12pm 06pm 12am

Rural Mountain Site:, Long range plume transport from the north when level are higher am 06am 12pm 06pm 12am 31 00am 06am 12pm 06pm 12am

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 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 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.

Field Work At T1 SITES ALONG THE WAY….

A tale of 2 Cities… Vegas: Jan thru Feb Daily variations small Mexico City: March Daily variations large