Limits on Ozone Air Quality Improvement in North American Megacities. David Parrish

Transcription

1 Mexico City 8-10 October 2018 Limits on Ozone Air Quality Improvement in North American Megacities David Parrish Independent Consultant Retired from: NOAA/ESRL Chemical Sciences Division Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Colorado USA

2 Mexico City 8-10 October 2018 Limits on Ozone Air Quality Improvement in North American Megacities Today: 1. Severe air pollution in urban areas is a long-standing problem. 2. Los Angeles and Mexico City both improved ozone air quality over decades. 3. What is the limit to which ozone could be reduced (based on the statistic on which the standard is judged)?

3 1. Severe air pollution in urban areas is a long-standing problem. Air pollution in Los Angeles in mid-20 th century was second to none Los Angeles smoggiest day occurred on Sept. 13, 1955, when ozone levels reached 900 parts per billion (ppb) - Newspaper report Photo from front page of the Sept. 15, 1955, Los Angeles Times

4 1. Severe air pollution in urban areas is a long-standing problem. Air pollution in Los Angeles in mid-20 th century was second to none Los Angeles smoggiest day occurred on Sept. 13, 1955, when ozone levels reached 900 parts per billion (ppb) - Newspaper report Photo from front page of the Sept. 15, 1955, Los Angeles Times

5 1. Severe air pollution in urban areas is a long-standing problem. Air pollution in Los Angeles in mid-20 th century was second to none 24-hour average PM 10 concentrations exceeded 600 µg/m 3 in Los Angeles (National Academy of Engineering Report, 2007) Peak PM 10 concentrations exceeded 1150 µg/m 3 in Beijing (Zheng et al., Atmos. Chem. Phys., 2015) Photo from front page of the Sept. 15, 1955, Los Angeles Times

6 2. Ozone air pollution in North American megacities has greatly improved. Great progress has been made in reducing ozone pollution in Los Angeles and Mexico City (as well as other U.S urban areas) Based on the same statistic, Mexico City maximum ozone was reached later, but improved more rapidly compared to Los Angeles Speculation: Mexico City may achieve lower ozone concentrations than Los Angeles not long after yr averages of the 4th highest 8-hr annual maxima U.S. NAAQS statistic Curves are polynomial fits Tremendous progress has been made in Los Angeles, but it required > 5 decades! Parrish, Singh, Molina, and Madronich (2011), Air quality progress in North American megacities: A review, Atmos. Environ., 45,

7 How was air quality improved in Los Angeles? Emissions from all sources addressed! - Open burning banned - Industrial emissions controlled - Electrical generation emissions controlled, or power plants moved elsewhere

8 How was air quality improved in Los Angeles? Emissions from all sources addressed! - Open burning banned - Industrial emissions controlled - Electrical generation emissions controlled, or power plants moved elsewhere - U.S. Urban Areas: Motor Vehicles dominate emissions

9 How was air quality improved in Los Angeles? Exhaust and evaporated fuel contain: Hydrocarbons (VOCs), Carbon monoxide (CO), Oxides of Nitrogen (NOx), and Primary PM VOCs + CO + NOx + sunlight gives O 3 and Secondary PM

10 How was air quality improved in Los Angeles? Ambient VOC and CO concentrations decreased by factor of ~50 in 5 decades Warneke et al., J. Geophys. Res., 2012

11 How was air quality improved in Los Angeles? Ambient VOC and CO concentrations decreased by factor of ~50 in 5 decades even while fuel use increased by factor of ~3 Per km traveled, modern U.S. vehicles emit ~1% of VOCs and CO compared to 1960 vehicles Warneke et al., J. Geophys. Res., 2012

12 How was air quality improved in Los Angeles? Ambient VOC and CO concentrations decreased by factor of ~50 in 5 decades Factor of ~4 even while fuel use increased by factor of ~3 NO X reductions much slower than VOC reductions Factor of ~50 Pollack et al., J. Geophys. Res., 2013

13 How was air quality improved in Los Angeles? Ambient VOC and CO concentrations decreased by factor of ~50 in 5 decades Factor of ~4 even while fuel use increased by factor of ~3 NO X reductions much slower than VOC reductions Response of O 3 above background was not proportional to VOC or NOx reductions Factor of ~10 Factor of ~50 Pollack et al., J. Geophys. Res., 2013

14 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? 3-yr averages of the 4th highest 8-hr annual maxima Ozone Design Values (ODVs) Parrish, Singh, Molina, and Madronich (2011), Air quality progress in North American megacities: A review, Atmos. Environ., 45,

15 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? Los Angeles area maximum ODVs 3-yr averages of the 4th highest 8-hr annual maxima U.S. NAAQS statistic Corresponds to ~98 th percentile over ½ year ozone season Parrish et al., J. Geophys. Res., 2017

16 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? Fit maximum ODVs to a simple mathematical function to RMSD = 5.3 ppb r 2 = 0.99 y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb t = 21.9 ± 1.2 years 3-yr averages of the 4th highest 8-hr annual maxima U.S. NAAQS statistic Corresponds to ~98 th percentile over ½ year ozone season Parrish et al., J. Geophys. Res., 2017

17 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? Fit maximum ODVs to a simple mathematical function to RMSD = 5.3 ppb r 2 = 0.99 y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb t = 21.9 ± 1.2 years Physical interpretation: y 0 : U.S. Background ODV i.e., the ozone design value that would exist if US anthropogenic precursor emissions were reduced to zero Parrish et al., J. Geophys. Res., 2017

18 How was air quality improved in Los Angeles? Ambient VOC and CO concentrations decreased by factor of ~50 in 5 decades Factor of ~4 even while fuel use increased by factor of ~3 NO X reductions much slower than VOC reductions Response of O 3 above background was not proportional to VOC or NOx reductions Factor of ~10 Factor of ~50 Pollack et al., J. Geophys. Res., 2013

19 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? Fit maximum ODVs to a simple mathematical function to RMSD = 5.3 ppb r 2 = 0.99 y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb t = 21.9 ± 1.2 years Physical interpretation: y 0 : U.S. Background ODV A: ODV enhancement above y 0 in 1980 t : e-folding time for decrease in ODV enhancement

20 Reduction in ozone pollution in Los Angeles has slowed (also in other U.S urban areas, and perhaps Mexico City). Why? Fit maximum ODVs to a simple mathematical function to There is a lowest possible ODV (i.e., the U.S. background ODV) from natural emissions and transport. As that limit is approached, reduction of ozone concentrations must slow and eventually stop. RMSD = 5.3 ppb r 2 = 0.99 y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb t = 21.9 ± 1.2 years Physical interpretation: y 0 : U.S. Background ODV A: ODV enhancement above y 0 in 1980 t : e-folding time for decrease in ODV enhancement

21 Compare NYC with Los Angeles Fit maximum ODVs to a simple mathematical function to RMSD = 5.3 ppb r 2 = 0.99 Los Angeles: y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb (1980) t = 21.9 ± 1.2 years New York City: y 0 = 45.8 ± 1.7 ppb A = 64 ± 3 ppb (2000) t set to 21.9 years RMSD = 3.5 ppb r 2 = 0.92

22 Compare NYC with Los Angeles Fit maximum ODVs to a simple mathematical function to Los Angeles: y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb (1980) t = 21.9 ± 1.2 years New York City: y 0 = 45.8 ± 1.7 ppb A = 64 ± 3 ppb (2000) t set to 21.9 years

23 Implications: U.S. background ODVs are 65% to 89% of 70 ppb NAAQS. Los Angeles: y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb (1980) t = 21.9 ± 1.2 years New York City: y 0 = 45.8 ± 1.7 ppb A = 64 ± 3 ppb (2000) t set to 21.9 years

24 Implications: U.S. background ODVs are 65 to 89% of 70 ppb NAAQS. U.S. background ODVs are larger than today s ODV enhancements from U.S. anthropogenic precursor emissions. Los Angeles: y 0 = 62.0 ± 1.8 ppb A = 197 ± 8 ppb (1980) t = 21.9 ± 1.2 years New York City: y 0 = 45.8 ± 1.7 ppb A = 64 ± 3 ppb (2000) t set to 21.9 years

25 Implications: U.S. background ODVs are 65 to 89% of 70 ppb NAAQS. U.S. background ODVs are larger than today s ODV enhancements from U.S. anthropogenic precursor emissions. To reach NAAQS, 2015 ODV enhancements must decrease by: -- 25% in New York -- factor of 4 in Los Angeles

26 Implications: U.S. background ODVs are 65 to 89% of 70 ppb NAAQS U.S. background ODVs are larger than today s ODV enhancements from U.S. anthropogenic precursor emissions. To reach NAAQS, 2015 ODV enhancements must decrease by: -- 25% in New York -- factor of 4 in Los Angeles Forward projections of trends suggest NAAQS will be reached much sooner in LA than NYC

27 What is background ozone in Mexico City? U.S. NAAQS = 70 ppb - 3-yr average of 4th highest 8-hr annual maxima Corresponds to ~98 th percentile over ½ year ozone season Mexico NAAQS = 70 ppb - 75th percentile of 8-hr annual maxima in year 3-yr averages of the 4th highest 8- hr annual maxima Ozone Design Values (ODVs) Parrish, Singh, Molina, and Madronich (2011), Air quality progress in North American megacities: A review, Atmos. Environ., 45,

28 What is background ozone in Mexico City? 6000 km Elevation 2.3 km

29 What is background ozone in Mexico City? At Mexico City s latitude, 6000 km to the west, 75 th percentile ozone is 40 ppb at 2-3 km. May be a reasonable estimate of the lower limit of Mexico NAAQS in Mexico City NOAA/GMD sondes - Hilo Hawaii

30 What is background ozone in Mexico City? At Mexico City s latitude, 6000 km to the west, 75 th percentile ozone is 40 ppb at 2-3 km. May be a reasonable estimate of the lower limit of Mexico NAAQS in Mexico City May be easier to reach NAAQS in Mexico City (background ~ 40 ppb) than Los Angeles (background ~ 62 ppb) 3-yr averages of the 4th highest 8-hr annual maxima Ozone Design Values (ODVs)

31 Mexico City 8-10 October 2018 Limits on Ozone Air Quality Improvement in North American Megacities Today: 1. Ozone concentrations cannot be reduced below a minimum background 2. Background is ~ 65 to 89% of 70 ppb U.S. NAAQS in New York City and Los Angeles 3. U.S. background ODVs are greater than today s ODV enhancements from U.S. anthropogenic precursor emissions. 4. Difficulty of reaching NAAQS depends strongly on magnitude of background - ~2021 in New York City, ~2050 in Los Angeles

32 Model calculated U.S. background ODVs: Models have some skill: r 2 values ~0.31 to Models average systematically lower by 4 to 12 ppb.

33 What is background ozone in Mexico City? At Mexico City s latitude, 6000 km to the west, 75 th percentile ozone is 40 ppb at 2-3 km. May be a reasonable estimate of the lower limit of Mexico NAAQS in Mexico City NOAA/GMD sondes - Hilo Hawaii

34 What is background ozone in Mexico City? At Mexico City s latitude, 6000 km to the west, 75 th percentile ozone is 40 ppb at 2-3 km. May be a reasonable estimate of the lower limit of Mexico NAAQS in Mexico City Sonde measurements in California are much higher than in the tropics NOAA/GMD sondes Trinidad Head, California