Environmental Chemistry and Toxicology TO… · Act emission standards limit S emissions to 260 g...

CHEM 3360 / TOX 3360 (W06) (Martos) W1/2 (page 1)

Environmental Chemistry and Toxicology

CHEM 3360 / TOX 3360

Class Notes for Winter Semester, 2006

Perry Martos, Ph.D., CIH


Overview:

Perspectives – what is pollution? • Generation and release of undesirable constituents or

physical “effects” in to the environment where acute or chronic exposure to those “effects” results in a response that has or can have an impact on the resulting life forms and/or non-life forms.1 o Air (volatile, semi-volatile, particulate,

particulate adsorbed materials) o Water (drinking water, wastewater, sewage) o Soil (usually non-volatile, water “insoluble”

materials) o Food (pesticides) (fruits, vegetables grown with

pesticides) o (Pathogens) o Radiation (alpha, beta, gamma) o Thermal o Noise (sea animals and sonar radiation)

• So, we understand that a large number of critical variables exist that may have an “effect” on life forms; regardless of whether they are measurable. Clearly, our ability (and opportunity) to control (man-made) pollution will benefit all life forms.

1 We cannot be anthropocentric and consider only humans require a habitable environment, particularly when we (humans) are not aware of the true complex relationships among the simplest of microorganisms and ourselves.


• In almost all cases, economic driving forces dictate whether a “control” opportunity is realized, and usually only in the most dire of circumstances are those issues aggressively implemented. Strong scientific, fact-based evidence will ultimately convince regulators and therefore industry and consumers to make changes favoring the longevity and preservation of life forms (besides humans), while simultaneously ensuring viability of the “economic engine”.

• Similarly, efforts are made to reduce, control and possibly eliminate sources of pollution in air, water, soil, food, and others. For example, vehicular emissions control in Ontario was implemented to reduce mass loading of “exhaust” in to the air. While still missing the mark on this, the Government nonetheless made an attempt to “reduce” automobile emissions for the benefit of Ontario’s life forms.

• What about emissions from coal fired power-generating stations? Recently, proposals were made by our Provincial Government to shut down coal-fired power generating stations in favour of enhancing nuclear driven power generating stations. Why? Look at the following diagrams.


Typical coal fired power plant. What are the environmental issues facing us here?

A fuel fired (CH4) steam power plant. What are the environmental issues facing us here?


A Nuclear reactor based power-generating station. What are the environmental issues facing us here?


• Question: A typical US coal burning power plant uses coal with an energy content of about 24 kJ/g and has an average carbon content of about 62%. Clean Air Act emission standards limit S emissions to 260 g SO2/1,000,000 kJ of heat input into the plant (130 g S/1,000,000 kJ). Particulate matter emissions are restricted to 13g/106 kJ. Assume the plant uses coal with 2% S and 10% unburnable emissions called ash. About 70% of the ash is released as fly ash and 30% settles out as bottom ash. Also assume the plant uses 3 units of heat energy (from the coal) to deliver 1 unit of electrical energy (typical). o Determine the SO2, particulate and C emissions

in g per unit kW-hour (assume all C is released to atmosphere)

o How efficient must the S control system be in order to meet the standards set in the question?

o If all the particulate matter is made up of fly ash, how efficient must the particulate control system be to meet particulate emission control emission limits?


• Consider a 1500 ft² home requiring electric heating. What is the positive environmental impact in increasing insulation in the attic from R-11 to R-40? The typical home is kept at 70°F and the outdoor temperature averages 32°F. What is the annual $ savings to the homeowner if the electricity costs 10 cents/kWhr? What is the reduction in atmospheric C, SO2 and particulate matter if 1 million such houses were upgraded as described? Given 3412 Btu/kWhr. o R-values are described in units of ft² °F hr/Btu.

o RTTA

q i )( 0−= , Where q is the rate of heat transfer

through a barrier (assuming the surface area A is perpendicular to the heat flow, air temperature Ti on one side of the barrier and T0 on the other side. The R-value in SI units is given in m² K/W (m² Kelvin / Watt).

• Consider 1 million homes utilizing refrigerators with energy efficiency ratings of 500 kWhr versus 650 kWhr. What is the reduction in pollution then?


Why are we concerned about airborne pollutants?

Six Common Air Pollutants http://www.epa.gov/air/urbanair/6poll.html

Carbon Monoxide Lead

Nitrogen Dioxide Ozone

Particulate Matter (PM) Sulfur Dioxide

(Carbon Dioxide)

Example: Health and Environmental Impacts of SO2 http://www.epa.gov/air/urbanair/so2/hlth1.html

• Respiratory Effects from Gaseous SO2 o Peak levels of SO2 in the air can cause temporary

breathing difficulty for people with asthma who are active outdoors. Longer-term exposures to high levels of SO2 gas and particles cause respiratory illness and aggravate existing heart disease.

• Respiratory Effects from Sulfate Particles o SO2 reacts with other chemicals in the air to form

tiny sulfate particles. When these are breathed, they gather in the lungs and are associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death.


• Visibility Impairment o Haze occurs when light is scattered or absorbed

by particles and gases in the air. Sulfate particles are the major cause of reduced visibility in many parts of the U.S., including our national parks.

• Acid Rain o SO2 and nitrogen oxides react with other

substances in the air to form acids, which fall to earth as rain, fog, snow, or dry particles. Some may be carried by the wind for hundreds of miles.

• Plant and Water Damage o Acid rain damages forests and crops, changes the

makeup of soil, and makes lakes and streams acidic and unsuitable for fish. Continued exposure over a long time changes the natural variety of plants and animals in an ecosystem.

• Aesthetic Damage o SO2 accelerates the decay of building materials

and paints, including irreplaceable monuments, statues, and sculptures that are part of our nation's cultural heritage.

Acid Rain: http://www.epa.gov/acidrain/

SO2:http://www.epa.qld.gov.au/environmental_management/air/air_quality_monitoring/air_pollutants/sulfur_dioxide/


• These examples illustrate impacts on the environment through usage of electricity, from the perspective of the homeowner; industrial activities in NA, however, dwarf all homeowner energy consumption and pollution generated combined.

• Similarly, vehicular emissions, unabated and controlled industrial activities, lead to broad scale pollutant issues in all areas: air, water, soil, and thermal. Manufacturing products for consumers keeps industry in business but at the expense of environmental mass loading of pollutants. Housing pressures have reduced farmland areas thus requiring pesticides to ensure high crop yields, or sometimes pesticides are used to control mosquitoes in the US and Canada (methoprene) for reasons of human safety (risk?).

• Since our atmosphere is the most ubiquitous of all the environmental mediums, it is logical to start with atmospheric chemistry. Delocalization and long-range transportation of pollutants through the air is simple (movement from the point source to everywhere else on the planet). During the lifetime of the pollutant though, tremendous environmental impacts can be realized. Following that, we will study water and metals in the environment.


Some Basics

Thermodynamics •Enthalpy, H:

The heat content of the reacting system reflects the number and kinds of chemical bonds; when reaction releases heat – exothermic; heat content of the products is less than that of the reactants; ∆H is negative when systems take up heat from surroundings–endothermic; ∆H is positive Endothermic (∆H > 0) and exothermic (∆H < 0)

•Entropy, S:

Inner tendency of a system to change (expand) and a measure of randomness of system; when products are less complex and more disordered than reactants; gain in entropy.

• First Law: The total energy of the universe is constant.

• Second Law: No process (biological, physical, or chemical) occur spontaneously unless it is coupled with an increase in the entropy of universe

Free energy (G, ∆G) is defined as available energy or useful work and relates enthalpy and entropy:

STHGo ∆−∆=∆ Equilibrium (∆G=0) and at non-equilibrium (∆G≠0)


Endergonic (∆G > 0) and exergonic (∆G < 0) Actual Free Energy Changes Depend on Reactant and Product Concentrations (concentrations are in mol/L).

aA + bB → cC + dD

beq

aeq

deq

ceq

eq BADC

K][][][][

=

)ln(][][][][

ln' eqbeq

aeq

deq

ceqo KRT

BADC

RTGG −=

−=∆−∆

At equilibrium, no force driving the reaction in either direction, 0=∆G

)ln(][][][][

ln eqbeq

aeq

deq

ceqo KRT

BADC

RTG −=

−=∆


Converting airborne concentrations of analyte from ppmv to mg/m³. Assume 1 ATM and 25°C Say you have 10 ppmv CO2 in air. This is 10 µL CO2/~1L air. Convert this volume of CO2 to mol. using n

RTPV

= …. molxnK

KmolatmL

Lxatm 76

1009.415.2980821.0

10101 −−

==⋅

⋅⋅⋅ .

Therefore, the number of g of CO2 is gx

molgmolx 57 1096.1481009.4 −− =⋅ . Now, recall that this was the

mass of CO2 in 1L of air at 1atm and 25°C. Now, convert 1 L air to 1 m³ air = 10-3m³ air. Therefore, we are left with:

)1,25³(@/6.19³10

1096.13

5

atmCmmgm

gx°=−

−

.

• It is extremely common to find concentrations of

airborne pollutants expressed in the dimensionless terms of ppmv and ppbv. The reason is that in those forms, no consideration is required for the temperature and pressure of the system. On the other hand, given humans breath in the order of 5 to 15 m³ of air per hour, it is quite common to express airborne concentrations of pollutants in mass/m³, typically ng/m³, µg/m³, or mg/m³ when discussing exposure to airborne pollutants in the occupational environment, in indoor air and in outdoor air.

Please DO NOT mistake ppmv with ppm in soil or water.


Mass Balance Expressions

Input rate =output rate + decay rate + accumulation rate

• Steady-State Conservative Systems

Input rate =output rate

• Steady-State Systems with Non conservative Pollutants

Input rate =output rate + decay rate

• Step Function Responses.

Input rate =output rate + decay rate + accumulation rate

Units Quantity Prefix Symbol

10-18 atto A 10-15 femto F 10-12 pico P 10-9 nano n 10-6 micro µ 10-3 milli m 10-2 centi c 10-1 deci d 10 deca da 102 hecto h 103 kilo k 106 mega M 109 giga G 1012 tera T 1015 peta P 1018 exa E


Some Useful Units and Conversions

Gas Chemistry

Gas pressure ↓with ↑altitude.

HxPP O41015.1 −−=

where P=atmospheric pressure at altitude H H=altitude (m) PO=atmospheric pressure at sea level (atm)

• Dalton’s Law of Partial Pressures • Boyle’s Law • Charle’s Law • Avogadro’s Principle • Combined Gas Law • Rauolt’s Law


• Henry’s Law (Solubility of Gases In Water) (W. Henry, 1903) o When air comes in contact with water, some of it

dissolves in the water o Different constituents of air and its impurities

(vapourized pollutants) partition in relation to T and water purity

o Several ways to describe this phenomenon

o gH PKX =

where X = mole fraction of the gas dissolved in liquid KH = Henry’s Law Constant (atm−1). Pg = the partial pressure of the gas in air (atm)

o Another way to describe it… TCC

Kaq

gH ,∞

∞

=

]2[][

...][][]2[][ 1

21

1

OHgas

gasgasOHgasX ≅

+++=

Since [H2O]=55.56 mol/L…we can write.

gH PKgas 56.55][ = . Using this equation, calculate the maximum concentration of O2 that can be dissolved in water at 25°C, at sea level. What about at 1500 m (in Denver). (answers: 8.3 / 6.8 mg/L).

Gas phase


Data from Tchobanoglous and Schroeder, 1985

T (°C) KHCO2 KHO2 0 0.001374 0.00003915 0.001137 0.000033

10 0.000967 0.000030315 0.000823 0.000027120 0.000701 0.000024425 0.000611 0.0000222

KHCO2 as a Function of Temperature

0.0006

0.0007

0.0008

0.0009

0.001

0.0011

0.0012

0.0013

0.0014

0 5 10 15 20 25T (°C)

KH

CO

2


Atmospheric composition

Major components N2 78%, O2 21%, Ar ~1%

Medium” components CO2 370 ppmv (↑1.5 ppmv/year) CH4 1700 ppbv H2O variable

Trace components H2 600 ppbv N2O 310 ppbv CO ~100 ppbv O3 <30 ppbv (clean troposphere)→82 ppbv (Canadian guideline)→300 ppbv Other hydrocarbons: low ppbv NOx low pptv-10 ppbv SO2 <1 ppbv

• Unique nature of Earth’s atmosphere: O2 present (photosynthesis)


Regions of the atmosphere and environmental problems Thermosphere (> 90 km) Mesosphere (~50-90 km) Stratosphere (~15-50 km) Troposphere (lower atmosphere, to ~ 15 km)

• Most of the mass of the atmosphere (~5×1015 tonnes) is present in the troposphere (~99% below 30 km)

Tropospheric Environmental Issues Greenhouse warming Photochemical smog Particulate Matter Acid precipitation

Stratospheric problems Ozone depletion

Residence times (simplified perspectives)

Definition #1 (kinetics) ∑ ′=

k1τ

Definition #2 (materials flow) MVC RR )(

=τ

CR is concentration of analyte in Reservoir (mass/volume) VR is volume of Reservoir (volume) M is the mass loading rate or mass removal rate (mass/time).

Note that CRVR can also be considered a static mass that is removed over time. Terms: reservoir; sources; sinks


Residence times of atmospheric gases –biologically regulated O2 (1.2 × 1015 t)/(4.0 × 1011 t yr-1) = 3.0 × 103 yr N2 (3.9 × 1015 t)/(3 × 108 t yr-1) = 1 × 107 yr CO2 (6.2 × 1011 t)/(3.7 × 1011 t yr-1) = 1.7 yr rate of increase 1.5 ppmv/yr H2O (1.3 × 1010 t)/(4.3 × 1011 t yr-1) = 3.0 × 10-2 yr (10 d) What does the following graph suggest?


Vapour pressure of water as f(temperature)

Relative Humidity (RH) is a value calculated to indicate the relative level of saturation of water vapour in air. Note that RH can be calculated using:

)(TPV

nRTPRH

sat

==


Solar energy and photochemical reactions • Photochemical reactions are caused, or accelerated, by

light (energy) • Sunlight can supply the energy to drive chemical

reactions that would otherwise be energetically unfavourable

• Absorption of light raises the substrate to an "excited" state

• Photochemical reactions require prior absorption of photons: 1 photon absorbed per atom or molecule

λhcE photon =

h=Plank's constant=6.626 x 10-34 J s

c=the speed of light=2.998 x 108 m s-1

λ=wavelength of light, m

Multiply by Avogadro's Constant to get the energy per mole ∆E, kJ mol-1 = (1.19 x 105)/λ, nm

• Example: Calculate the energy of o (i) one photon of wavelength 530 nm o (ii) a mole of photons of wavelength 530 nm.

• [Answers: 3.7 × 10-19 J; 225 kJ mol-1]


Ranges of radiation Visible 400(blue) to 700(red) nm UV-A 400-325 nm UV-B 325-295 nm (limit of λ reaching the surface) UV-C <295 nm (present in upper atmosphere)

Energy as a function of Wavelength of UV and visible radiation

Wavelength, nm Energy, kJ mol-1

700 170

500 240

400 300

300 400

Question: The C-Cl bond has bond dissociation energy 330 kJ mol-1, while CFCl3 absorbs radiation having λ < 220 nm. Will CFCl3 undergo bond cleavage in the lower atmosphere? [Answer: 330 kJ mol-1 corresponds to λ = 360 nm]. NO!


Temperature profile of the atmosphere: the importance of sunlight (photochemistry)

Thermosphere, mesosphere: radiation < 200 nm is absorbed N2 → 2N and N2 → N2

++e- (followed by recombination)


Stratosphere: radiation 200-300 nm is absorbed by O2 O2→→O3 (followed by O3→→O2) These processes convert solar radiation (light) into heat

• Radiation > 300 nm reaches the Earth’s surface. The lowest part of the troposphere is warm because the earth radiates infrared radiation which is trapped by the atmosphere

Greenhouse gases and climate change • Greenhouse effect = trapping of outgoing infrared

radiation by “radiatively active gases” • Physical chemistry: infrared radiation always

accompanied by a change of dipole moment in the lower and upper vibrational states

• Above rule means that the following do NOT absorb IR: N2; O2; Ar. These are the major constituents of the atmosphere.

Conclusion: Trace gases are responsible for IR absorption in the troposphere: H2O; CO2; O3; CH4; N2O; CFCs (chlorofluorocarbons) But, without IR absorption the average surface temperature of earth would be ~-30°C rather than ~ +15°C. “Greenhouse effect” as commonly understood means increased IR trapping due to increases in the concentrations of CO2; CH4; N2O; CFCs → warming of the troposphere

• Potential positive feedback from H2O if temperature increases (recall Henry’s Law)


• Definition: Global Warming Potential. o A quantified measure of the globally averaged

relative radiative forcing impacts of a particular greenhouse gas. The cumulative radiative forcing (both direct and indirect effects) integrated over a period of time from the emission of a unit mass of gas relative to some reference gas (IPCC 1996).

o CO2 (reference gas)


CO2: Atmosphere and Ocean The pH in natural waters is controlled with the carbonate system. It is the most important acid-base system in natural waters.

CO2(g)↔CO2(aq)↔H2CO3(aq)↔HCO3−(aq)↔CO3

2−(aq)↔CaCO3(s) H2CO3 Carbonic Acid HCO3

- Bicarbonate Ion CO3

2- Carbonate Ion

CO2(g)↔CO2(aq)+H2O↔H2CO3↔H++HCO3−

HCO3−↔H++CO3

2−

If limestone is present CaCO3(s)↔Ca2++CO3

2− then, can have feedback to CO2(g).

What is the pH of Natural Rainwater? (~5.6). We will work through this in a future section. For now, we need to appreciate that our water systems are a sink for CO2, but that the balance between being a sink a source of CO2 is fine.


Issues: • How fast will the oceans take up injections of CO2

into the atmosphere? o t½ for uptake into surface water=1.3 years o for exchange between surface and deep water t½

=35 years

• What would be the effect of an increase in water

temperature? o CO2(aq)→CO2(g) equilibrium constant KH

increases with T, hence possibility of positive feedback.


• Is global warming a fact? Is it due to increased concentrations of greenhouse gases? Are human activities to blame?

[Figures from 2001 Report of the International Panel on Climate Change]


Historic Increases of CO2, CH4, and N2O [IPCC Report] Data are from ice cores in Antarctica and Greenland, supplemented in recent years by direct atmospheric analysis.


What is the Kyoto Agreement? International agreement reached in 1990 for developed countries to cut back their CO2 emissions by 6% from their 1990 levels. The 2001 IPCC Report suggests that temperature increases of >3/C are likely before 2100; this would greatly change the climate in many regions Controversies: easier for some countries than others, depending on their “energy mix” Not all commentators agree that human activities are to blame Even if the cause is human activities, it may seem pointless for only a few countries to meet their targets Canada is a huge fossil fuel user per capita, but does not contribute a high percentage of the world’s total CO2 budget. Canada, like most other countries, will not impose a carbon tax. Canada is arguing for carbon credits for agriculture and reforestation. Quebec is on a collision course with Alberta, because Alberta is a source of fossil fuels, whereas Quebec generates hydroelectricity. What should be done? Immediately reduce emissions of greenhouse gases? Adjust to changed climatic conditions?


Suggested Solutions:

• Reduce emissions by vehicles: o Improved fuel efficiency - Ontario "Drive Clean"

program, California's greenhouse gas law o New power sources for vehicles: o Ethanol fuel - Sunoco's ethanol-in-gasoline

expected to reduce CO2 emissions by 130,000 tonnes/yr (equiv. to taking over 23,000 cars off the road)

o ethanol sources = wood/cellulose, grains & oil crops eg. corn, wheat and barley economical and ecological impact?

o Natural gas • Hybrid electric vehicles (Toyota Prius; NYC buses) • Hydrogen vehicles - USA, commercial hydrogen

fueling station • Bio-diesel - animal fats, vegetable oils from soybean,

canola, corn, sunflower SERIOUS PROBLEMS with Ethanol as a fuel from corn….What is the energy cost to generate 1L of ethanol. Consider the harvesting costs, the refinery costs, the delivery costs. In actuality, energy realized from burning 1L of ethanol is significantly lower than the energy required to deliver 1L of ethanol to gas tank. Why does it seem feasible? Subsidies!!! No real, net positive environmental impact realized. Proof will be provided later.


Stabilization of Atmospheric CO2 Levels [IPCC Report]


• Predicted Changes in Global Temperatures


• Global Precipitation Map


• Predicted Sea Level Rise (concerns?)


• Lower emissions standards for industry: o Global efforts are forcing more efficient

processes and clean-up prior to discharge. • Alternative sources of electricity:

o Solar energy - Australian tower, new technology, costly.

o Wind - fastest growing energy source, potential to provide 12% of global electricity by 2020? well established, cost?

o Tidal forces - Hammerfest, Norway; considerable potential, renewable, but costly, unknown problems re: maintenance, ecological impact

o Nuclear and hydroelectric - 75% of electricity produced by Ontario, minimal emissions

• Find new sinks or uses for excess greenhouse gases o Methane hydrates - USA; proposals to harness

the released methane as a fuel source o CO2 storage - injection into deep ocean, deep

saline aquifers (potential problems: leaks causing asphyxia, pH reductions, e.g. Mammoth Mountain (http://wrgis.wr.usgs.gov/fact-sheet/fs172-96/) displacement of brine into overlying aquifers?)

o Liquid CO2 solvent - similar properties to pyridine, already replaced methylene chloride for decafination of coffee, safer, cannot be oxidized, does not react to free radicals (Env. Sci. Technol. v36 Sept. 1/02).

Environmental Chemistry and Toxicology TO… · Act emission standards limit S emissions to 260 g...

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Transcript of Environmental Chemistry and Toxicology TO… · Act emission standards limit S emissions to 260 g...