Ground-level ozone Brian I. Magi Associate Professor of Atmospheric - - PowerPoint PPT Presentation

1 Image from NASA

Brian I. Magi

Associate Professor of Atmospheric Sciences

UNC Charlotte, Department of Geography and Earth Sciences

Ground-level ozone

Presentation at Mecklenburg County Air Quality Commission meeting, 28 August 2017

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Picture of ground-level ozone

(it’s invisible)

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Image from wikipedia

Air pollution kills 3 million people per year worldwide. Diabetes kills 1.5 million. AIDS kills 1 million. Malaria kills 450,000. Air pollution kills more people than diabetes, AIDS, and malaria combined!

Sources: http://www.who.int/mediacentre/news/releases/2016/air-pollution-estimates/en/ http://www.who.int/features/factfiles/malaria/en/ http://www.who.int/gho/hiv/en/ http://berkeleyearth.org/air-pollution-and-cigarette-equivalence/

Pollutant Primary/ Secondary Averaging Time Level Form Carbon Monoxide primary 8-hour 9 ppm Not to be exceeded more than once per year 1-hour 35 ppm Lead primary and secondary Rolling 3 month average 0.15 μg/m3 Not to be exceeded Nitrogen Dioxide primary 1-hour 100 ppb 98th percentile of 1-hour daily maximum concentrations, averaged over 3 years Ozone primary and secondary 8-hour 0.070 ppm Annual fourth-highest daily maximum 8- hr concentration, averaged over 3 years Particle Pollution (Particulate Matter

• r PM)

PM2.5 primary 24-hour 12 μg/m3 Annual mean, averaged over 3 years PM10 primary and secondary 24-hour 150 μg/m3 Not to be exceeded more than once per year on average over 3 years Sulfur Dioxide primary 1-hour 75 ppb 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years

EPA Criteria Pollutants

Concentrations from the National Ambient Air Quality Standards (NAAQS) that are scientifically determined to minimize harmful air quality

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AQI Values Pollution Level 0 to 50 Good 51 to 100 Moderate 101 to 150 Unhealthy for Sensitive Groups 151 to 200 Unhealthy 201 to 300 Very Unhealthy 301 to 500 Hazardous

Determining the AQI relative to NAAQS

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Measure pollutant concentration Convert to AQI Every pollutant has its own AQI Highest AQI at that particular time is the reported AQI

Three main types of smog:

• 1. Smoky fog (smog) or the classic London Smog

2.Photochemical (ozone) smog

• 3. Particle (PM2.5) smog

6 This is particle smog in Beijing

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Ozone is NOT EMITTED. Ozone forms via gas chemistry that is

completely dependent on nitrogen dioxide (𝑂𝑃2) 𝑂𝑃2 + 𝑡𝑣𝑜𝑚𝑗𝑕ℎ𝑢 → 𝑂𝑃 + 𝑃 𝑃 + 𝑃2 + 𝑁 → 𝑃3 + 𝑁 𝑃3 + 𝑂𝑃 → 𝑂𝑃2 + 𝑃2 This chemistry shows that 𝑃3 depends on the ratio of

𝑂𝑃2 𝑂𝑃

If 𝑂𝑃2 increases more than 𝑂𝑃, then 𝑃3 will increase, but 𝑃3 itself is destroyed by reaction with 𝑂𝑃. These reactions help explain background 𝑃3 but not pollution levels.

𝑃3 𝑂𝑃 𝑂𝑃2

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The key to understanding photochemical smog is to introduce new chemical pathways that convert 𝑂𝑃 to 𝑂𝑃2 without destroying 𝑃3 (big red arrow)

𝑃3 𝑂𝑃 𝑂𝑃2 𝑃3 𝑂𝑃 𝑂𝑃2

New chemical pathways

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The key to understanding photochemical smog is to introduce new chemical pathways that convert 𝑂𝑃 to 𝑂𝑃2 without destroying 𝑃3

Bring in the humans!

𝑃3 𝑂𝑃 𝑂𝑃2

New chemical pathways are introduced when:

VOCs and NOx concentrations increase in the presence of sunlight

*Volatile organic compounds and NOx is NO2 and NO (nitrogen oxides)

𝑊𝑃𝐷𝑡 break down chemically and are then oxidized by 𝑂𝑃 to form 𝑂𝑃2

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𝑃3

𝑂𝑃 𝑂𝑃2 𝑊𝑃𝐷𝑡 break down chemically and are then oxidized by 𝑂𝑃 to form 𝑂𝑃2 As 𝑂𝑃2 increases, then the pathway to 𝑃3 increases in strength and we get smog!

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VOC concentration NO concentration NO2 concentration Ozone concentration

Daytime: Ozone increase follows an NO2 increase Overnight: Ozone is depleted by NOx

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Mecklenburg County

Winds typically blow from SW to NE VOCs and NOx are produced in center city Transport means highest O3 should develop downwind

Check air quality at https://www.mecknc.gov/LUESA/AirQuality/Air-Quality- Data/Pages/default.aspx and UNC Charlotte Urban Institute, Wikipedia, and Mecklenburg County Air Quality “Mobile Source Indicators” report for various county stats 2014.

Garinger H.S. (Ozone, PM2.5, NO2, CO, SO2) Montclaire E.S. (PM2.5) Charlotte-Douglas University Meadows (Ozone) Remount Road (PM2.5, NO2, CO)

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Figure is based on data in the very useful 2012 AQC report available at: https://www.mecknc.gov/luesa/airquality/educationandoutreach/pages/aqc.aspx

Mecklenburg County Snapshot Stationary sources – what we see being permitted at AQC (facilities, manufacturing, etc.) Area sources – include a wide variety of mostly stationary sources, and sometimes (but not always) permitted. Examples include dry cleaners, gas stations, lawnmowers, BBQs. …Restaurants (I think) Mobile sources – planes, trains, automobiles, etc. The number 1 problem!

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Great webpage of recent AQI:

https://www.mecknc.gov/LUESA/AirQuality/Air-Quality-Data/Pages/recent.aspx

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Useful interactive tool for seeing how pollution, meteorology, and human activities interact: Smog City!

(not the brewing company in LA link)*. Smog city program is at http://www.smogcity2.org/

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Summary

• Ozone is not emitted
• Ozone forms as a biproduct of NO2 breakdown by high

temperatures and sunlight

• NO2 itself increases via VOC breakdown
• Ozone forms during the day
• Transport of precursors (NOx and VOCs) can cause
• zone to form downwind
• Ozone precursors are mainly emitted by mobile sources
• Ozone pollution is only aspect of any pollution event

Email if you have any questions brian dot magi at uncc.edu