Midterm Matters any appeals regarding the test must be communicated to Dr. Gentleman by THURSDAY, NOVEMEBER 4 Next week: Lab #4

What’s coming up??? Oct 25The atmosphere, part 1Ch. 8 Oct 27Midterm … No lecture Oct 29The atmosphere, part 2Ch. 8 Nov 1Light, blackbodies, BohrCh. 9 Nov 3Postulates of QM, p-in-a-boxCh. 9 Nov 5,8Hydrogen atomCh. 9 Nov 10,12Multi-electron atomsCh.10 Nov 15Periodic propertiesCh. 10 Nov 17Periodic propertiesCh. 10 Nov 19Valence-bond; Lewis structuresCh. 11 Nov 22Hybrid orbitals; VSEPRCh. 11, 12 Nov 24VSEPRCh. 12 Nov 26MO theoryCh. 12 Nov 29MO theoryCh. 12 Dec 1Putting it all together Dec 2Review for exam

More about our atmosphere Last time we discussed some aspects of stratospheric chemistry –This is mostly all about ozone Today we will look at some chemistry which happens in the troposphere (below about 12 km altitude)

Solar illumination on earth Pretty much all the energy which drives the earth comes as radiation from the sun Light absorbed by ozone in ozone layer

In the troposphere most chemistry starts with ozone and UV light … and often ends with CO 2 –For example, oxidation of methane, whose balanced equation is: CH O 2  CO H 2 O O 3 + UV  O* + O 2 O* + H 2 O  2 OH OH + CH 4  H 2 O + CH 3 CH 3 + O 2  CH 3 OO CH 3 OO + NO  NO 2 + CH 3 O CH 3 O + O 2  HCHO + HO 2 HCHO + UV + 2O 2  2HO 2 + CO CO + OH + O 2  CO 2 + HO 2 NO 2 + UV  NO + O O + O 2  O 3 HO 2 + NO  NO 2 + OH

Troposphere NO 2 + UV  NO + O O + O 2  O 3 NO + O 3  NO 2 + O 2 HO 2 + NO  NO 2 + OH Stratosphere O 2 + UV  O + O O + O 2  O 3 NO + O 3  NO 2 + O 2 O + NO 2  NO + O 2 Interesting note: the role of NO and NO 2 in the troposphere is quite different from in the stratosphere. At lower altitudes, there is not the correct UV radiation (not enough energy, since it’s already been absorbed higher up!!)to form O atoms from O 2 … tropospheric O (and so O 3 ) is formed from NO 2

So we see that NO reacts with radicals to make NO 2, which reacts with sunlight and oxygen to make ozone Ozone reacts with sunlight and water to make hydroxyl radicals (OH) Hydroxyl radicals react with most substances to make oxidized products These reactions all involve formation and destruction of free radicals… they are examples of chain reactions

OH + NO 2  HNO 2 CH 3 COO + NO 2  PAN The radical chains are broken by reactions which form products such as nitric acid and PAN : O 3 + UV  O* + O 2 O* + H 2 O  2 OH OH + CH 4  H 2 O + CH 3 CH 3 + O 2  CH 3 OO CH 3 OO + NO  NO 2 + CH 3 O CH 3 O + O 2  HCHO + HO 2 HCHO + UV + 2O 2  2HO 2 + CO CO + OH + O 2  CO 2 + HO 2 Radicals!

The NO comes from the reaction of N 2 with O 2 at high temperatures: –N 2 + O 2  2 NO  H 0 f (NO) = kJ/mol (what would le Chatalier say?) Cars, trucks, buses, etc. Power plants and factories Lightning Hydrocarbons (such as methane) come from transport, power plants, ruminant animals, rice paddies, trash dumps, …

Urban air pollution involves the same chemistry as we just saw, but more intense The timing of photochemical smog generally tracks rush hours, and requires sunlight and warm enough (> 18 0 C) temperatures

Emitted from cars Formed from NO + radicals Formed from NO 2 + light Formed from NO 2 + radicals

We can help reduce such air pollution by using better engine designs and technology

Organics O3O3 OH H2OH2O H2OH2O Particles -soot, PM 2.5 Urban films -grime on windows Chemistry affects all aspects of the lifetimes and fates of pollution compounds. Air pollution NO x

For example, the uptake of water by organic particles to form haze on a polluted summer day: the oxidation state matters! Increasing O : C ratio

Oleic acid, and similar fatty acid compounds, are present in animal and plant cells. These compounds are observed in atmospheric particles due to ablation from leaves and from cooking

Water uptake by oleic acid before and after oxidation by ozone CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOH Before exposure After exposure

Amber Asad ( a UTSC student) measuring how water is sorbed by oleic acid

And the result … Organic compounds + Oxidants (ozone, OH, …) + Water + Sunlight

We saw how organic carbon (ie- methane) is transformed to carbon dioxide in the atmosphere. Note that CO is formed, along the way. Carbon monoxide is also a product of “incomplete combustion”, in much the same types of process as we saw earlier. CO is problematic because it is a poison to oxygen-breathers like us. The way in which oxygen is transported in the blood is by binding to haemoglobin – a molecule in our red blood cells. It turns out that CO is better at binding to haemoglobin, so oxygen is blocked.

Sulfuric acid is another important atmospheric molecule: it is a primary source of acid rain (along with nitric acid, which we saw before) and, because it is very, very hygroscopic, it acts as a condensation site for water vapour H 2 SO 4 is formed in the atmosphere by the oxidation of sulfur-containing compounds (mostly from biological processes) to SO 2, then to the acid SO 2 is a product of combustion and also is emitted by volcanoes

Once formed, SO 2 reacts in the atmosphere: SO 2 + OH  HSO 3 HSO 3 + O 2  HO 2 + SO 3 SO 3 + H 2 O  H 2 SO 4 The sulfuric acid may be in the gas phase (where it will form water droplets) or dissolved already Acid rain in this part of North America is mostly this acid

Apart from air pollution, human introduction of hydrocarbons and their oxidation products into the atmosphere affects the carbon cycle

These compounds, especially ones such as carbon dioxide, methane and halocarbons, can influence the heat balance in the troposphere by absorbing heat radiation (infrared light) emitted from the earth (“global warming”). The earth’s surface is warm enough to sustain life because of a greenhouse effect due to water vapour and some CO 2. By increasing the concentrations of greenhouse gases, we are altering this effect

Most of the observed warming in the past 50 years is attributable to human activities