Скачать презентацию Class objectives Cover some of the major

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Class objectives: • Cover some of the major topics in Environmental Chemistry • • Energy Atmospheric Compartment Water compartment Soil

1. Some examples of environmental chemicals • • Polynuclear Aromatic HC (PAHs) Dioxins Ketones PCBs CFCs DDT O 3, NO 2, aerosols, SO 2

Toxic loads • Scientists have hypothesized that the fetus is sharing the mother’s toxic load, and may actually provide some protection to the mother by reducing her internal exposure.

• Children get 12% of their lifetime exposure to dioxins during the 1 st year. • Their exposure is 50 times greater than an adult during a very critical developmental period.

• Firstborns from dolphins off the coast of Florida usually die before they separate from their mothers

Mother’s milk • Human babies nursed by mothers with the highest PCB contamination levels in their milk are afflicted with more acute ear infections than bottle fed Inuit babies. • Many of these children don’t seem to produce enough antibodies for childhood vaccinations to take.

PCBs and lower intelligence • There is evidence of lower intelligence in babies exposed to PCBs. • In adults, a blood-brain barrier insulates the brain from many potentially harmful chemicals circulating through the body • In a human child this barrier is not fully developed until 6 months after birth.

2. Energy

SO what is a joule? ? Force = mass x acceleration; f = m x a a = D velocity / D time = dv/dt velocity = D distance / D time; a= D distance / D time 2 Work = force x distance W = f x d W= m x a x d and W = m x d 2 /t 2 Work and energy have the same units a joule is defined as accelerating 1 kg of mass at 1 meter/sec 2 for a distance of 1 meter A watt is a unit of power = 1 joule/second or energy/time

how long will the oil last? ? 1980 estimate of reserves Oil 1 x 1022 J 1980 estimate of oil usage /year 1. 35 x 1020 J/year Estimate the # years of oil left if we used at the above rate from 1980 to 1990 and 2 x’s the 1980 rate after 1990 = 3 x; we estimated ~50 to 80 years We used more recent data in class.

Fuel energy §When we burn a fuel where does the energy reside? §Let s take hydrogen in water as an example. If we were to react H 2 with O 2 to form water, we would 1 st have to break the hydrogen bonds and the oxygen bonds §This takes energy; in the case of H 2 it takes 432 k. J/mole (~100, 000 calories/mole) for H 2 2 H. §How many days of food will supply you with 100, 000 calories? §To break O 2 to O. (O 2 2 O. ) requires 494 k. J/mol §When water forms, however, we get energy back from the formation of H 2 O because new bonds are formed. Which ones? ?

Combustion energies from different fuels (k. J) react. per per moles heat mole gram CO 2 per k. J O 2 fuel 1000 k. J hydrogen 482 241 2 H 2+O 2 2 H 2 O 120 0 Gas 810 405 810 52 CH 4 + 2 O 2 CO 2 +2 H 2 O 1. 2 Petroleum 1220 407 610 44 2 (-CH 2 -)+ 3 O 2 2 CO 2 +2 H 2 O 1. 6 Coal 2046 409 512 39 4 (-CH-)+ 5 O 2 4 CO 2 +2 H 2 O 2. 0 Ethanol 1. 6 1257 419 1257 27

3. Basic concepts • Where does p. V=n. RT come from? • At standard state can you calculate R? • A+B C+D ln Keq =-DH/R x 1/T + const.

4. The atmospheric compartment

Two important features the atmospheric Compartment are temperature and pressure

Why does the temperature normally decrease with height in the troposphere and increase with height in the stratosphere? ?

The pressure or force per unit area udecreases with increasing altitude u. The decline in pressure (P) with altitude is approximately = to log P= - 0. 06 (z); where z is the altitude in km and P is bars

How thin is the air at the top of Mt. Everest? u. Mt. Everest is 8882 meters high or 8. 88 km high ulog P = -0. 06 x 8. 88 u. P = 10 -0. 06 x 8. 88 = 0. 293 bars u. Assume there are 1. 01 bars/atm. u. This means there is < 1/3 of the air

The quantity d is called the dry adiabatic lapse rate u. Air that contains water is not as heavy and has a smaller lapse rate and this will vary with the amount of water u. If the air is saturated with water the lapse rate is often called s u Near the surface sis ~ 4 o. K/km and at 6 km and – 5 o. C it is ~6 -7 o. K/km

How does air circulate u. At the equator air is heated and rises and water is evaporated. u. As the air rises it cools producing large amounts of precipitation in equatorial regions. u. Having lost its moisture the air mass moves north and south. u. It then sinks and compresses (~30 o. N and S latitude) causing deserts

u. The mean residence time (MRT) can be expressed as: MRT = mass / flux where flux is mass/time u. If 75% of the mass/year in the stratosphere comes from the troposphere u 1 MRT = --------- = 1. 3 years – 0. 75/year

u. Mt. Pinatubo in the Philippines erupted in June 1991, and added a huge amount of SO 2 and particulate matter the stratosphere. After one year how much SO 2 was left? u. For a 1 st order process C= Coe -1 year/ MRT u. C/Co= e -1 year/ MRT = e -1/1. 3= 0. 47 or ~ 50% uin 4 years, C/Co= e -4 years/1. 3 years = ~5%

u. What happened to global temperatures after the Pinatubo eruption? u. A lot of SO 2 was injected into the atmosphere u. SO 2 forms fine sulfate particles that reflect light back into the atmosphere and this cools the upper troposphere

5. What is Global Warming and how can it Change the Climate?

How fast are green house gases increasing? ? ? itime trace for the concentration of carbon dioxide from 1958 -1992 at Mt. Mauna lowa Hawaii i. Why does it oscillate up and down as it generally goes up? ?

How fast is Global Warming Occurring? i. The rate of global warming over the next century may be more rapid than any temperature change that has occurred over the past 100, 000 years!!! i. This will cause major geographical shifts in forests, vegetation, and cause significant ecological disruption

1979 perennial Ice coverage Nat. Geographic, Sept 2004)

2003 perennial Ice coverage

Doubling Emissions of CO 2 i. Often discussed are the effects of doubling CO 2 concentrations from pre-industrial times (2 xpre-Ind. CO 2=550 ppm) i. Some times predications are made with the assumption of CO 2 doubling or even quadrupling. i. On the next slide you will see world wide emissions using different assumptions.

Including Particles in Global Models i. Fine particles, especially sulfate particles resulting from SO 2 emissions from coal, combustion can reflect light from the sun and actually cause a negative temp. effect i. The next 2 picture from a global circulation model (GCM by Bob Charleston, UW-Wash, USA), shows a cooling effect in the industrialized world. First without considering particles then with ired= +2 o. C, yellow =+3 o. C, blue = +10 C

red= +2 o. C, yellow =+3 o. C, blue = +10 C

red= +2 o. C, yellow =+3 o. C, blue = +10 C

6. Kinetics: 1 st order reactions A ---> B -d [A] /dt = krate [A] - d [A]/[A] = kratedt [A]t= [A]0 e-kt

Some time vs conc. data Hr Conc [A] Ln[A] 0 2. 718 1 0. 3 2. 117 0. 75 0. 6 1. 649 0. 50 0. 9 1. 284 0. 25 1. 2 1. 000 0. 00 1. 5 0. 779 -0. 25

A plot of the ln[conc] vs. time for a 1 st order reaction gives a straight line with a slope of the 1 st order rate constant.

ln [A]/[A]o=-k t 1/2 ; ln 2 /k =t 1/2 2 nd order reactions A + B products d. A/dt = k 2 nd [A][B] If B is constant kpseudo 1 st = k 2 nd [B]

kpseudo 1 st = k 2 nd [B] ln 2 /k =t 1/2 1. constant OH radicals in the atmosphere kpseudo 1 st = k 2 nd [OH. ]

7. Stratospheric o 3 The Stratosphere begins about 10 k above the surface of the earth and goes up to 50 k The main gases in the stratosphere, as at the surface, are oxygen and nitrogen uv light of low wave lengths ( high energy) split molecular oxygen (O 2 ) to split oxygen O 2 O. + O. requires 495 k. J mole-1 of heat (enthalpy) What wave length of light can do this? ? Let’s start with hn = E, where h is Planck’s constant and n is the frequency of light and E is the energy associated with one photon.

And, n l = c where c is the speed of light and l is the wave length of light Combining we can solve for the wave length that will break apart oxygen at an enthalpy of 495, 000 J mole-1 l= h c/ E If the value of Planck’s constant is 6. 62 10 -34 joules sec c = 2. 9979 x 108 m sec-1 l= h c/ E = 241 nm can you verify this calculation? Hint energy E is for one photon? ?

Paul Crutzen in 1970 showed that NO and NO 2 react catalytically with O 3 and can potentially remove it from the stratosphere. (he get’s a nobel prize for this in 1995) NO + O 3 NO 2 + O 2 NO 2 + O. -> NO + 2 O 2 So where would NO come from? ? SST’s

CCl 3 F + uv Cl. +. CCl 2 F but the free chlorine atom can react with O 3 Cl. + O 3 Cl. O. (chlorine oxides) + O 2 what is really bad is that Cl. O. + O. Cl. + O 2 Remember that: O. + O 2 O 3 (Ozone) It is estimated that one molecule of chlorine can degrade over 100, 000 molecules of ozone before it is removed from the stratosphere or becomes part of an inactive compound.

Molina found in 1985 that HCl could be stored on the surface of small nitric acid particles in polar stratospheric clouds (PSC). The HCl then just had to wait for a Cl. O-NO 2 to hit the particle Cl 2 + uv Cl. + Cl. These nitric acid particles form under extremely low temperatures in polar stratospheric clouds HCl Cl. O-NO 2 Cl 2

8. What are aerosols? • Aerosols are simply airborne particles • They can be solids or liquids or both • They can be generated from some of the following sources: 1. combustion emissions 2. atmospheric reactions 3. re-entrainment

Cooking stir-fried vegetables: Kamens house, 1987, EAA data

u. Anthropogenic sources u. Primary aerosol Industrial particles 100 x 1012 g/year soot 20 forest fires 80 u. Secondary aerosols sulfates from SO 2 140 organic condensates 10 nitrates from NOx 36 usum of Anthropogenic 390 x 1012 g/year usum of natural sources 3070 x 1012 g/yea

What are some of the terms used to describe aerosols? • Diameters are usually used to describe aerosol sizes, but aerosols have different shapes.

Often particles are sized by their aerodynamic diameter • The aerodynamic diameter of a particle is defined as the diameter of an equivalent spherical particle (of unit density) which has the same settling velocity. • It is possible to calculate the settling velocity of a spherical particle with a density =1

Fresh wood soot in outdoor chambers (0. 5 mm scale

Gas Particle Partitioning toxic gas particle

Langmuirian Adsorption (1918) gas surface • = fraction of total sites occupied • Rateon= kon (Pg) (1 - ); • Rateoff= koff ; • kon/koff= Keq

Langmuirian Isotherm • • if Keq Cgas<< 1; = Keq Cgas

Yamasaki et al. (1982) • Langmuirian adsorption • • Assumes total # sites TSP (particle conc) • log Ky = -a(1/T)+ b

Yamasaki (1982) • Collects Hi-vol filters+PUF • Analyzes for PAHs filter Ba. A log Ky PUF 1/Tx 1000

Partitioning & uptake by the lungs • Nicotine (Pankow’s group)

Killer Particles

Mortality vs. particle exposure 1. 3 1. 2 mortality 1. 1 ratio 1. 0 10 20 30 40 2. 5 mm particle conc. in mg/m 3 • On a mass basis urban fine particles may be more toxic than cigarette smoke

Samet et al. at UNC exposed human airway epithelial cells to residual oil fly ash (ROFA) particles • cells secreted prostaglandins • Prostaglandins are a class of potent inflammatory mediators which play a role in inflammatory, immune and functional responses in the lung