Edition A Project of the American Chemical Society Chapter 2 The Air We Breathe What is air What are the components that make up the air we breathe How does the composition of air change from place to place ID: 759127
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Slide1
Chemistry in Context, 9th Edition
A Project of the American Chemical Society
Slide2Chapter 2The Air We Breathe
What is air? What are the components that make up the air we breathe?How does the composition of air change from place to place?What are the impurities in air and how did they get there?Are there harmful components in the air you breathe indoors?Are there ways we can prevent or limit contaminants from polluting our atmosphere?
Slide3The Troposphere
75% of our air, by mass, is in the troposphere, the lowest region of the atmosphere in which we live.
Slide4The Composition of Air
It’s a mixture – a physical combination of two or more substances present in variable amounts.
Slide5What’s in a Breath?
SubstanceInhaled Air (%)Exhaled Air (%)Nitrogen (N2)78.078.0Oxygen (O2)21.016.0Argon (Ar)0.90.9Carbon dioxide (CO2)0.044.0WaterVariableVariable
Slide6What Else Is In a Breath?
These images show Beijing, China from the same vantage point on different days.In addition to nitrogen, oxygen, and other colorless gases, there are harmful nitrogen oxides and particulate matter that contribute to air pollution.
Slide7Air Inversions
Cooler air can be trapped beneath warmer air due to weather conditions.Pollutants often accumulate in the cooler air of an inversion layer.This situation is worsened when air flow is limited, such as in cities surrounded by mountains.
Slide8Visualizing the Molecules in Air
A molecule is a fixed number of atoms held together by chemical bonds in a certain spatial arrangement.The chemical formula symbolically represents the type and number of each element present. Chemists use three viewpoints to study and understand matter, macroscopic, symbolic, and particulate.
Slide9Molecular Structures
The particulate view of matter shows the 3-D molecular structure, with atoms color-coded.
Slide10Naming Binary Compounds
Prefixes are used to designate the number of each type of element:
NumberPrefix1mono2di3tri4tetra5penta6hexa7hepta8octa9nona10deca
Slide11Naming Binary Compounds of Nonmetals
Prefixes are used to designate the number of each type of element:N2O = dinitrogen monoxide (also known as nitrous oxide, or laughing gas)P2O5 = diphosphorus pentoxide
Slide12Naming Hydrocarbons
Hydrocarbons are compounds containing only carbon and hydrogen atoms
Chemical FormulaNumber of Carbon AtomsCompound NameCH41MethaneC2H62EthaneC3H83PropaneC4H104ButaneC5H125PentaneC6H146HexaneC7H167HeptaneC8H188OctaneC9H209NonaneC10H2210Decane
Slide13Air Pollutants: Risk Assessment
Risk Assessment – evaluating scientific data and making predictions in an organized manner about the probabilities of an occurrence. Toxicity – intrinsic health hazard of a substance.Exposure – the amount of the substance encountered.Evaluate the risk of breathing the amount of ozone in the air between the hours of 4:00 p.m. and 6:00 p.m. where you live. Note: You may have to go online to access information from the EPA to help in your calculation.
Slide14Concentration Terms
Parts per hundred (percent)Atmosphere is 21% oxygen = 21 oxygen molecules per 100 molecules and atoms in airParts per million (ppm)Midday ozone levels reach about 0.4 ppm: Parts per billion (ppb) Sulfur dioxide in the air should not exceed 30 ppb:
Slide15Concentration Conversions
21% means 21 parts per hundred…means 210 parts per thousandmeans 2,100 parts per ten thousandmeans 21,000 parts per hundred thousandmeans 210,000 parts per million
The difference between
% and ppm is a factor of 10,000.
Slide16The Harmful Few…
These gases represent the most harmful for our health and the health of our planet:Carbon monoxideOzoneSulfur dioxide (SO2) and nitrogen dioxide (NO2)Particulate matter (PM)
Slide17U.S. National Ambient Air Quality Standards
PollutantStandard (ppm)Approximate Equivalent Concentration (mg/m3)Carbon monoxide1-hour average3540,0008-hour average910,000Nitrogen dioxide1-hour average0.100200Annual average0.053100Ozone8-hour average0.070140ParticulatesPM10, 24-hour averageN/A150PM2.5, 24-hour averageN/A35PM2.5, annual averageN/A15Sulfur dioxide1-hour average0.0752103-hour average0.501,300
Slide18Air Quality Monitoring and Reporting
The average concentration of air pollutants in the United States have decreased dramatically since 2000.
Slide19The Number of Unhealthy Days Per Year
Although air quality has improved in recent years, on average, people in some metropolitan areas breathe air containing unhealthy levels of pollutants.
Metropolitan AreaOzonePM2.5Boston08Chicago100Cleveland101Houston210Los Angeles430Phoenix114Pittsburgh141Sacramento3513Seattle20Washington, DC212
Slide20EPA’s Air Quality Index
Slide21Example: Air Quality Index Values for Phoenix, AZ
Variations reflect those in the local weather patterns. Regional events such as forest fires and volcanic eruptions can influence air quality.
Slide22Chemical Reactions
Chemical reactions are characterized by the rearrangement of atoms when reactants are transformed into products.This is an example of a combustion reaction.The number of atoms on each side of the arrow must be equal (Law of Conservation of Mass).
Slide23Balancing Equations
Tips for balancing equations:If an element is present in just one compound on each side, balance it firstBalance anything that exists as a free element lastBalance polyatomic ions as a unitCheck when done – same number of atoms, and same total charge (if any) on both sides
Slide24Balancing Equations: An Example
As an example, consider the combustion of methane (CH4) to generate carbon dioxide (CO2) and water (H2O):When balanced, there is 1 carbon atom, 4 oxygen atoms, and 4 hydrogen atoms on either side of the equation.
Slide25“Incomplete Combustion”
If the amount of oxygen is altered, the hydrocarbon can burn incompletely:2 Verify that both of these equations are properly balanced!
Slide26Vehicle Emissions
This U.S. auto emissions report shows the amount of CO generated from the exhaust, which can tell if the vehicle is operating properly or exhibits incomplete combustion products.
Slide27Direct Source of Sulfur Trioxide
Sulfur trioxide then reacts with water to produce sulfuric acid, a contributor to acid rain. The good
n
ews: Since 1985, we have seen a 55% reduction in SO2 emissions in the U.S.
Slide28The Complexities of Nitrogen Dioxide Formation
NO2 is a brown gas, giving smog its characteristic brown tinge.i) ii) NO2 is also produced from the reaction with ground-level ozone:Volatile Organic Compounds (VOCs) emitted from vehicle exhausts are also involved in NO2 production:’A’ + ’’ + NO2
Slide29Vehicle Catalytic Converters
Catalytic converters reduce the amount of carbon monoxide (CO) in the exhaust due to catalyzing the combustion of carbon monoxide to carbon dioxide (CO2).Newer designs also limit the release of nitrogen oxides by reducing them to nitrogen and oxygen gases.
Slide30AIRNOW Website: Local Air Quality Conditions and Forecasts
The EPA AirNow website provides information regarding particulate matter and ozone concentrations for local regions in the U.S. This shows that the ozone concentrations in southern California peak around mid-afternoon and drop overnight. Sunlight is needed to produce ozone from VOCs and nitrogen oxides.
Slide31Ozone (O3): A Secondary Pollutant
Unlike nitrogen and sulfur oxides that are direct pollutants, ozone is a “secondary pollutant”. It is produced from one or more other pollutants (VOCs and NO2):i) ii)
Slide32Indoor Air Pollutants?
Do you think of harmful pollutants when you light your incense candle or want to begin painting a room in the house? Why do you think these are considered indoor air pollutants?
Slide33What is “Green Chemistry”?
The EPA Design for the Environment Program initiated green chemistry programs. Green chemistry reduces pollution through the design or redesign of chemical processes.“Green” processes use less energy, create less waste, use fewer resources, and use renewable resources. Some examples include:Plastics synthesized from renewable sources instead of typical fossil-fuel derived precursors.Paints that contain fewer volatile organic compounds (VOCs)Cheaper and less wasteful ways to produce consumer products.Limiting or eliminating the use of organic solvents.Removing arsenic from the touchscreens of portable electronic devices.