Lupita Paredes-Miranda & W. Patrick Arnott Atmospheric Sciences Program

1. 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

2. REFERENCES AND ACKNOLEDGEMENTS Jerome Fast: PNNL Jeffrey Gaffney & Nancy Marley: University of Arkansas

3. 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)

4. LAT N 19 00 LONG W 99 Altitude 2240 m to 3700 m North to South Area: 1 964 375Km²

5. ~23,000,000 people in 2005 >4,000,000 Motor vehicles About Mexico City…

6. 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

7. Scale 25 miles between IMP and U of Tecamac Scale 65 miles between IMP and La Biznaga

9. 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

10. Biomass Burning Contributes to the Regional Air Pollution MODIS Satellite Image 2 March 2004 marine stratus common biomass burning sites (red)

11. 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

12. ~ 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

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

14. Relatively clean afternoon at T0, IMP (located in Northeast MC) looking southwest.

15. 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 >> 

16. 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

17. 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

18. Schematic of the Photoacoustic instrument with scattering sensor LASER

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

20. Inlet System at T0

21. 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.

22. 1 Day = 1 hr = 2 m/s wind speed = 4.48 mph Arrow tail marks the day and the hour of the day

23. WESTERLIES EASTERLIES

24. 12am 06pm 12pm 31 06 21 26 11 16 06am 00am

25. 12am 06pm 12pm 06am 31 00am 06 21 26 11 16

26. 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

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

28. 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.

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

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

31. 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.

32. Cooling effect Warming effect Afternoon. Well mixed atmosphere. Regional SOA, dust and local emissions mix. Morning rush hour. Large amounts of black carbon aerosol.

33. 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

34. 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

35. A Tale of 2 Cities… Vegas: Jan thru Feb Daily variations small Mexico City: March 15 Sunrise: 6:45 am Sunset: 6:45 pm

36. Las Vegas Nevada sits in a basin Site Location, E Charleston Typical Surface Wind Direction Typical Wind Speed: 2 mph (daily average)

37. 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

39. 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.

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