2a air chemistry

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Air Chemistry GISAT 112 Types of Matter • Gases, liquids, solids • Air pollutants – Gases – Particulate matter • Can be either solid or liquid • Often a combination of both Table 1.5 Classification of Matter Chemistry in Context: Applying Chemistry to Society, 3e A Project of the American Chemical Society Copyright © 2000 by the American Chemical Society All Rights Reserved The Parts of an Atom • Atoms normally have – or more protons (+1 charge) – or more neutrons (no charge) – or more electrons (-1 charge) • Chemistry depends on the number of electrons, which in turn depends on the number of protons • Thus, the identity of an element is determined by the number of protons in its nucleus Number of protons Rounded, approximates the “Mass Number” – # of protons and neutrons Inorganic and Organic Compounds • Organic compounds: carbon-based chemicals • Some examples– C3H8 (propane; a hydrocarbon) – C2H5OH (ethanol; an alcohol) – CH3COOH (acetic acid; an organic acid) – C6H4Cl2 (dichlorobenzene; a chlorinated hydrocarbon) • Inorganic compounds: chemicals other than those based on carbon (although some contain carbon, e.g., as carbonates) • Some examples– NaCl (table salt) – H2O – SO2 (sulfur dioxide) – CaCO3 (limestone) – Fe2O3 (rust) Reactions and Equations • Reactants → Products • For example, consider combustion of carbon: C (s) + O2 (g) → CO2 (g) • Note that matter and number of atoms are conserved! Note: these aren’t necessarily Characteristics of Chemical Reactions true for nuclear reactions! Balancing Chemical Equations • Since the number of atoms of each element involved is conserved, the equations describing chemical reactions must be “balanced” • E.g.: _ CH4 + _ O2 → _ CO2 + _ H2O • Hint: Start with the most restricted terms 2 Atmospheric and Weather Terms • Troposphere: the part of the atmosphere from ground level to 10-12 km height Comprises about 80% of the mass of the atmosphere and nearly all of the water vapor, clouds, precipitation, and air pollutants • Stratosphere: the layer of the atmosphere from 10-50 km above the surface of the Earth Contains about 20% of the mass of the atmosphere Few air pollutants get this far (but there are important exceptions) Here is where oxygen and ozone filter out most of the dangerous UV light from the sun Atmospheric and Weather Terms (cont.) • Plume: the zone downwind of a pollutant source where the concentration of pollutants is higher than background • Atmospheric stability: the level of air velocities due to wind (mostly horizontal movement) and temperature differences (that can create vertical movement) Pollutants tend to stay concentrated in stable air and disperse rapidly in unstable air • Inversion: in the troposphere, the air temperature generally decreases with height above ground Under inversion conditions, the temperature increases Inversions are temporary, but they create stable air and cause pollution to become more concentrated while they last Supporting Concepts • Units of concentration, units conversions • Ideal gas law, molar volumes • Significant figures Units for NAAQS • ppm, ppb for gases • μg/m3 for particles (and gases) (μg/m3 = micrograms per cubic meter) Parts Per Million (or Billion) • For gases, the basis is VOLUME – i.e., volume of pollutant per volume of air • For example, ppm of a gaseous pollutant is m3 of pollutant per million (10 6) m3 of air • Or, liter of pollutant per million liters of air, etc Similarly, ppb is per billion (10 9) volumes of air Conversion: % to ppm 0.036m CO2 0.036% CO2 = 100m air Multiply both sides by 10,000: 0.036m CO2 10,000 0.036% CO2 = * 100m air 10,000 360m CO2 = 360 ppm 10 m air Moles and Atomic Weight • A mole of anything is Avogadro’s Number (6.022 x 1023) of those things A mole of a chemical is therefore 6.022 x 10 23 molecules – For reference: the universe is thought to have existed for about 1018 seconds! • The atomic weight of an element is the weight of one mole of those atoms – We can find this on the periodic table – E.g the atomic weight of carbon is about 12 g/mole Molecular Weight • The molecular weight (sometimes called “formula weight” ) of a chemical substance is the weight of one mole of its molecules in grams – The molecular weight of water is 18 g/mole • Why? Molecular Weight • The molecular weight (sometimes called “formula weight” ) of a chemical substance is the weight of one mole of its molecules in grams – The molecular weight of water is 18 g/mole • Why? – One mole of water (H2O) is therefore 18 grams of water – The molecular weight of table salt (NaCl) is 58.5 g/mole One mole of table salt weighs 58.5 grams Ideal Gas Law • The Ideal Gas Law describes quite accurately how most gases, under typical environmental conditions, respond to changes in those conditions • PV = nRT P = total pressure (in atmospheres) V = volume (in liters) n = number of moles of the gas R = gas constant (0.0821 L·atm/mole·K) T = absolute temperature (in K, which is °C + 273) Molar Volume • The molar volume of an ideal gas at atm and 0°C is 22.4 liters • For more typical environmental conditions of 20-25°C, the molar volume is approximately 24 L/mole Unit Conversions: ppm or ppb μg/m3 • For most calculations, we can assume the gaseous pollutant behaves as an ideal gas • At typical ambient temperatures (20-25°C) and atmospheric pressure, one mole of an ideal gas occupies about 24 L (22.4 L at 0°C) [molar volume ≅ 24 L/mole] • One mole of any chemical substance weighs its molecular weight in grams 78; mole = 78g) (e.g., MW of benzene = Unit Conversions: ppm or ppb μg/m3 • Example: convert 10 ppm of benzene ⇒ ? μg/m3 – MW of benzene = 78 g/mole (or 78 x 106 μg/mole) – 10 ppm = (10L benzene/106L air)  10 Lb 10 ppm =   10 Lair  78 x10 ug b  1000 Lair   24 L m b air     = 32,000 mug3  – Similarly, 10 ppb ≅ 32 μg/m3 • For more precise calculations and significantly different temperatures or pressures, use the Ideal Gas Law [...]... pollutant is 1 m3 of pollutant per 1 million (10 6) m3 of air • Or, 1 liter of pollutant per million liters of air, etc Similarly, ppb is per billion (10 9) volumes of air Conversion: % to ppm 3 0.036m CO2 0.036% CO2 = 100m 3 air Multiply both sides by 10,000: 0.036m 3 CO2 10,000 0.036% CO2 = * 3 100m air 10,000 360m 3 CO2 = 360 ppm 6 3 10 m air Moles and Atomic Weight • A mole of anything is Avogadro’s... of pollutants is higher than background • Atmospheric stability: the level of air velocities due to wind (mostly horizontal movement) and temperature differences (that can create vertical movement) Pollutants tend to stay concentrated in stable air and disperse rapidly in unstable air • Inversion: in the troposphere, the air temperature generally decreases with height above ground Under inversion conditions,... Conversions: ppm or ppb μg/m3 • Example: convert 10 ppm of benzene ⇒ ? μg/m3 – MW of benzene = 78 g/mole (or 78 x 106 μg/mole) – 10 ppm = (10L benzene/106L air)  10 Lb 10 ppm =  6  10 Lair  78 x10 6 ug b  1000 Lair   3 24 L m b air     = 32,000 mug3  – Similarly, 10 ppb ≅ 32 μg/m3 • For more precise calculations and significantly different temperatures or pressures, use the... air and cause pollution to become more concentrated while they last Supporting Concepts • Units of concentration, units conversions • Ideal gas law, molar volumes • Significant figures Units for NAAQS • ppm, ppb for gases • μg/m3 for particles (and gases) (μg/m3 = micrograms per cubic meter) Parts Per Million (or Billion) • For gases, the basis is VOLUME – i.e., volume of pollutant per volume of air
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