Introduction to Ozone

Nate Herbst

Southern Ute Indian Tribe

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Introduction

• What is ozone?• Where does it come from?• Why is it bad?• How do we monitor for it?

All animation in today’s presentation is provided courtesy of the NASA Goddard Space Flight Center Scientific Visualization Studio.

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Basic Chemistry• Nature= basic building blocks called elements• Ozone = molecule with 3 oxygen atoms

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Basic Chemistry (cont.)

• Elements in periodic table shown in atomic forms

• Atoms can combine to form molecules• Atoms and molecules make up the universe

around us

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Atoms and Molecules

• Most elements don’t exist as atoms• Most elements need more electrons than they

actually have• To get electrons they need, most atoms take

electrons from, or share electrons with, other atoms to form ions and molecules

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Drawing Molecules• Spheres representing nuclei• Lines beside them representing electrons

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An Oxygen Atom

• Atomic oxygen consists of 1 oxygen atom• The oxygen atom has 3 electron pairs

(needs 4)• Unstable, needs more electrons

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• To get 4th electron pair, oxygen atoms can share with other atoms

• Results in stable molecules

An Oxygen Atom (cont.)

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• Most common form of oxygen is diatomic (2- atom) molecule

• This is what we breathe• Notice each oxygen atom in molecule has 4

electron pairs• Very stable

The Oxygen Molecule

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The Ozone Molecule

• Ozone is a tri-atomic oxygen molecule, consists of 3 oxygen atoms

• Only 1 of these atoms has 4 electron pairs• Very unstable

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Ozone Is Very Reactive• Ozone is unstable, will react with anything it

can to get 4 electron pairs• Ozone reactivity has positive and negative

qualities• Ozone absorbs UV rays• Can react very strongly with body tissues

and many other things, such as plants

Ozone casts a shadow in U.V radiation (it absorbs some of the radiation). Photo courtesy of University of Wisconsin General Chemistry Class.

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Two Types of Ozone• Stratospheric ozone- protects our planet by

absorbing UV radiation

• Tropospheric (ground-level) ozone-harmful, designated as criteria pollutant

Ozone absorbing UV radiation. Animation by NASA.

Ozone reactivity. Animation by NASA.

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Ground-Level Ozone• This class focuses on ground-level ozone• “Ozone” refers to ground-level ozone• Corrosive air pollutant• Dangerous at high concentrations• EPA requires ozone monitoring to ensure

NAAQS isn’t surpassed

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Health Effects of Ground-Level Ozone

• Respiratory problems, irritates asthma, decreases lung function

• Affects– Children, elderly – Those with asthma,other lung problems– People who spend significant time outdoors and

exercising• Others…

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Other effects– Main precursor of smog– Dangerous to animals – Damages vegetation – Damages materials– Others…

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Ozone standard

• 8-hour standard for Ozone: 0.080 ppm

• Ozone level must be kept below this standard

• More about this later

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• Ozone is not directly emitted

• Ozone forms from precursor molecules – anthropogenic, biogenic and pyrogenic

sources

• Meteorological conditions are also important in ozone formation

Ozone Formation Is Very Complex

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• Nitrogen Oxides (NOx) and Volatile Organic Compounds (VOCs) required to form ozone

• Can be locally emitted or transported• NOx consists of Nitric oxide (NO) and

Nitrogen dioxide (NO2)

• Many types of VOCs

NOx and VOCs Ozone

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Majpr sources of NOx and VOCs

• Industrial facilities

• Mobile source exhaust

• Utility companies

• Chemical solvents

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• Most important precursor condition is sunlight

• Ozone formation requires sunlight• Other meteorological conditions are also

important– Temperature, wind, precipitation, relative

humidity, others

Ozone Precursor Conditions

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O3 Dependence on Meteorology

Example of ozone dependence on meteorological conditions(Ute 1 monitoring site - 8/13/02)

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14:24 14:52 15:21 15:50 16:19 16:48 17:16 17:45 18:14

Time

O3 (ppb), RH (%)

O3

RH

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• NO + VOCs NO2 + O2

• NO2 + hv (sunlight) O + NO

• O + O2 O3

• If not enough VOCs, ozone will replace and no net ozone will result

Ozone Formation Chemistry

Animation shows NO NO2 and NO2 O+NO. Animation by NASA.

Animation shows atmospheric ozone formation but the net process (O+O2O3) is the same. Animation by NASA.

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Ozone Formation Reaction (Cont.)

Net reaction

Oxygen atom

[ 3 electron pairs]

Oxygen molecule

[4 electron pairs each]

Ozone molecule

[4, 5 and 3 electron pairs, respectively]

Animation shows atmospheric ozone formation but the net process (O+O2O3) is the same. Animation by NASA.

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More about NOx, VOC’s and O3

• NOx (NO and NO2) and VOC’s react to form ozone

• NO can form and “scavenge” ozone (depends on VOC’s)

• Control strategies must address both NOx and VOC’s NOx, VOC's and Ozone

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8 13 18 23 28

NO (ppb)

O3 (ppb)At constant [VOC]

O3

NO forming Ozone

NO scavenging Ozone

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Ozone Scavenging

Example of ozone being scavenged by NO(Ute 1 monitoring site - 8/13/02)

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19:40 20:09 20:38 21:07 21:36 22:04 22:33

Time

O3, NO2, NOx (ppb)

O3

NOx

NO2

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Good Control Strategies Work

EPA 2003 trends report – 4th max 8hr ozone averages are dropping nationwide, due to effective control strategies!

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Hypothetical Graph (Xs of VOCs)

Ozone formation vs. precursor conditions (xs VOC)

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Time of day

O3 & NOx [ppb], precursors

Ozone [ppb]

Temperature [o C]

VOCs [ppb]

Sunlight [AU]

NO X [ppb]NO 2 [ppb]NO [ppb]

NO + VOCs ?

NO2 + O2

NO2 + sunlight ?

NO + O

O + O2 ? O3

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Hypothetical Graph (Few VOCs)Ozone formation vs. precursor conditions (constant VOC)

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0 2 4 6 8 10 12 14 16 18 20 22

Time of day

O3 & NOx [ppb], precursors

Ozone [ppb]

Temperature [o C]

Sunlight [AU]

NO X [ppb]NO 2 [ppb]NO [ppb]

NO + VOCs ? NO2 + O2

NO2 + sunlight ?

NO + O

VOCs [ppb]

O + O2 ? O3

NO + O3 ? NO2 + O2

With no XS VOCs all ozone formed is used to oxidize NO. There is no net O3 formed.

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Actual Graph (6/1/02)Ute 3 June 1st '02 ozone vs. precursor conditions

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0 2 4 6 8 10 12 14 16 18 20 22

Time of day

O3 & NOx [ppb], precursors

Ozone [ppb]

Temperature [o C]

Sunlight [AU]

NO X [ppb]NO 2 [ppb]NO [ppb]

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Ozone-Formation Movies

• Ozone formation associated with NOx and VOCs (from pyrogenic sources) - temperature also important here (Indonesia 1997)

• Global ozone formation (May 1997 – May 1998)

Ozone in Indonesia ’97. Animation by NASA.

Global ozone ’97-’98. Animation by NASA.

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Ozone Analysis

• Ozone analysis performed using EPA reference method

• Ozone absorbs 240nm U.V radiation • By determining UV absorbance, ozone

concentration can be known• We’ll discuss this later

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U. V. Photometric Absorption

Quick schematic of ozone U.V absorption analysis

Ozone absorbing U.V radiation.

Animation by NASA.

Zero air Ambient airU.V. Lamp Detector

The amount of U.V light leaving cell #1 corresponds to [O3]

The amount of U.V light leaving cell #2 provides your blank.

Photo courtesy of University of

Wisconsin General Chemistry Class.

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Summary

• Ground level ozone is a dangerous pollutant

• Must be maintained below standard• Ozone formation is complex, involves

different precursor molecules and conditions

• Ozone monitoring is important• Ozone monitoring should be included in

any air quality program