Photochemical Smog - Water Management - Lecture Slide, Slides of Water and Wastewater Engineering

Download Photochemical Smog - Water Management - Lecture Slide and more Slides Water and Wastewater Engineering in PDF only on Docsity! Photochemical Smog 1 Docsity.com Photochemical Smog • Background: Measurements • Sources and Chemical Processes ➔ Mobile Sources ➔ Trends in Mobile Emissions ➔ Photochemical Nitrogen Cycle ➔ Hydrocarbons • Smog Concentrations Around Los Angeles ➔ Influence of Weather and Terrain ➔ Trends 2 Docsity.com • Most air pollution is from combustion ➔ Internal Combustion Engines (ICE) in transportation is one significant source Source of Smog Pollutants Ideally: Consider the simplest hydrocarbon as a fuel: In this case, the only pollutant emitted is CO2, a greenhouse gas (more on that later). Fuel + O2 → CO2 + H2O CH4 + 2O2 → CO2 + 2H2O 5 Docsity.com ➔ In reality, combustion is not perfect due to incomplete mixing or power requirements. ➔ Less O2 may be consumed than required by stoichiometry. A more realistic representation: HC: methane, partially broken down methane, and some polymerized methane fragments. Also, air is not pure O2! CH4 + O2 → CO + CO2 + 2H2O + HC 6 Docsity.com In addition, we use complex fuels such as gasoline, oil, and coal, all of which contain impurities—metals, S, ash, Pb, N, and so forth. As a result there are emissions of CO, NOx, Pb, particulate matter, etc. N2 + O2 + heat → "thermal NOx" Fuel + O2 + N2 + → CO + CO2 + H2O + HC + NOx + Pb + PM + 7 Docsity.com Air Quality Criterion Air Quality Index (AQI) Description Good 0–50 No health impacts are expected when air quality is in this range Moderate 51–100 Unusually sensitive people should consider limiting prolonged outdoor exertion Unhealthy for Sensitive Groups 101–150 Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion Unhealthy 151–200 Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion Very Unhealthy (Stage-1 Alert) 201–300 Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion Air Quality Index 10 Docsity.com • Hydrocarbons are not a criteria pollutant but they are closely studied because of their role in ozone formation. • Almost all of the emission information data gathered by government agencies is focused on the criteria pollutants. • Emissions in the United States have leveled off or decreased since the 1970’s—when air pollution legislation began. Next figs: http://www.epa.gov/ttn/chief/trends/trends98/chapter3.pdf VOCs + NOx + sunlight → photochemical smog 11 Docsity.com Indexed to 1970 250 200 150 100 50 Figure 3-1. Trend in Gross Domestic Product, Population, Vehicle Miles Traveled, Total Fuel Consumption, combined VOLATILE ORGANIC COMPOUND and NITROGEN OXIDES Emissions, and SULFUR DIOXIDE Emissions, 1970 to 1998 === GDP == Population —=—VMT ~~ Total Fuel Consumption =*— VOC and NOx Emissions $02 Emissions pop gg dd a 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 Year 12 Docsity.com  Figure 3-3. Trend in NITROGEN OXIDE Emissions, 1940 to 1998 30 nN a nN o = a 1 = o nl Emissions (million short tons) 0 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 Year GFuel Combustion @ Industrial Processing OOn-+oad O Non-road @ Miscellaneous Note: Some fuctuatons in the years before 1970 am the result of diferent mehoddagies 1995 15 Docsity.com  Figure 3-5. Trend in SULFUR DIOXIDE Emissions, 1940 to 1998 oe a oe o nN a nl id o = a Emissions (million short tons) = o a n T 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Year 0 HEBER Pep pep pay TPP ttt ttt tt tt ttt ttt Trt tt GFuel Combustion Bindustrial Processing OOn-road ONon-+oad OMiscellaneous Nate: Some fuctuations in the years before 1970 are the meult of diferent methodobges 16 Docsity.com  Figure 3-6. Trend in PARTICULATE MATTER (PM 4) Emissions Excluding Fugitive Dust Sources, 1940 to 1998 = o = o = > = nN = o Emissions (million short tons) o o S ny 0 1940 1945 1950 1955 1960 1965 1970 Year 1975 1980 1985 1990 GFuel Combustion @ Industrial Processing DOn-+oad O Non-road @ Miscellaneous 1995 17 Docsity.com  Emissions (million short tons) Figure 3-8. Trend in LEAD Emissions, 1970 to 1998 300 250 nN Ss o 8 = Ss o 3 1970 1975 1980 1985 1990 1995 Year G Fuel Combustion Bindustrial Processing O On-road ONon-road O Miscellaneous 20 Docsity.com But many Americans still live in places where air quality standards are not met. 21 Docsity.com PM10 (particles < 10 µm) PM2.5 (particles < 2.5 µm) 22 Docsity.com OZONE FORMATION Ozone is one of the important air pollution problems in Los Angeles. Let’s consider the chemistry of ozone formation, and the connection of emissions and meteorology. 25 Docsity.com • Ozone is not directly emitted into the atmosphere, but is produced by a series of reactions involving: ➔ Oxides of nitrogen (NOx) ➔ Hydrocarbons (HC or VOCs/ROGs) ➔ Sunlight (hν) Ozone in Smog 26 Docsity.com NOx (NO and NO2) atmospheric reactions produce ozone Ozone is also consumed when it reacts with NO The actual O3 concentration for this set of reactions depends on the relative rate of each reaction. where M is some other substance (usually N2 or O2) NO2 + hν → NO + O 3P( ) O 3P( ) + O2 + M → O3 + M O3 + NO → NO2 + O2 27 Docsity.com • Another important radical: OH• This really wants to be water again and it will rip a hydrogen atom right out of your Grandma’s lungs, if its convenient. • How OH forms: O3 + hν → O 1D( ) + O2 O 1D( ) + H2O → 2OH• 30 Docsity.com • General hydrocarbon compound designated as: RH Hydrocarbon Chemistry • No ozone formed yet; however, • Photodissociation of NO2 forms O3, and reaction with NO destroys O3. • Hydrocarbons convert NO to NO2 without using up ozone RH + OH → R• + H2O R• + O2 → RO2• RO2• + NO → RO• + NO2 31 Docsity.com Completing the set of hydrocarbon reactions: RH + OH → R• + H2O R• + O2 → RO2• RO2• + NO → RO• + NO2 RO• + O2 → HO2 + ′R CHO HO2 + NO → NO2 + OH 32 Docsity.com This is a classic example of a chain reaction. The net effect is the OH• is regenerated, and NO is oxidized to NO 2 , which then forms O 3 . The reactions would run away were it not for the chain termination reaction: Nitric acid is very soluble in water and is responsible for most of the acidity in rainwater in LA, and in much of the West. Also, ➡ Leads to particle formation in Riverside OH + NO2 → HNO3 HNO3,g + NH3,g → NH4NO3,s 35 Docsity.com • If the hydrocarbon has > 1 C atom, multiple atoms of NO can be converted to NO2 as the hydrocarbon is oxidized to CO2. • The other product (R´CHO) is an aldehyde (in some cases it is a ketone or other oxygenated or nitrated organic ➔ Some of these products are quite toxic; many are not HNO3 (g) + NH3 (g)! NH4NO3 (s) 36 Docsity.com • Aldehydes like formaldehyde and acrolein are “air toxics” ➔ They are often more reactive than their parent hydrocarbons, so they tend to speed up the formation of smog. Formaldehyde HCHO Acetaldehyde CH3CHO Acrolein CH2CHCOH 37 Docsity.com • Timing of emissions ➔ Emissions during the morning are more effective than evening emissions in generating smog ➔ Simultaneous emissions magnify smog. • Distribution of sources ➔ More distributed emissions are less likely to result in high pollutant levels ➔ Densely concentrated urban areas focus emissions. 40 Docsity.com • Prevailing meteorology ➔ To get smog, need high temperatures, sunlight, and a temperature inversion. • Regional topography ➔ Mountain barriers, valleys or lowlands, plateaus affect the flow if air and dispersion of pollutants ➔ Land/sea breezes and marine boundary layers influence pollutant formation. 41 Docsity.com Torrance Newport Beach 42 Docsity.com  OZONE - 1998 Number of Days Exceeding the Federal Standard (1-hour average > 0.12 ppm) $242u> x ST AIR BASIN (SCAB) —-— COUNTY LINES AIR MONITORING 2 STATION ? 25, text JUNE 1996 VERSION agi rrataeratertvevsvtatonsterteonreTeneeetey ™ NOT EXCEEDED mm 1-40 ~~ OVER 40 DAYS 45 Docsity.com  OZONE — 1998 Number of Days Exceeding the Federal Standard (8-hour average > 0.08 ppm) @ AR WONTORING STATION ? 25 wits JUNE 1996 VERSION ™ NOT EXCEEDED mm 1-40 40-80 l@® OVER 80 DAYS 46 Docsity.com  SUSPENDED PARTICULATE (PM10) - 1994 ANNUAL ARITHMETIC MEAN, ug/m? COUNTY LI AIR MONITORING STATION MILES APRIL 1295 VERSION — — Federal Standard NOTEXCEEDED {MM§50-60 °" OVER 60 47 Air Quality Criterion Air Quality Index (AQI) Description Good 0–50 No health impacts are expected when air quality is in this range Moderate 51–100 Unusually sensitive people should consider limiting prolonged outdoor exertion Unhealthy for Sensitive Groups 101–150 Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion Unhealthy 151–200 Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion Very Unhealthy (Stage-1 Alert) 201–300 Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion Air Quality Index 50 Docsity.com November 6, 2007 11:00 am PST Los Angeles Region Ground-Level Ozone verside \ Banning \ 51 Docsity.com  Los Angeles Region Ground-Level Ozone . Ty Pasadena i ‘\ Be Hollywoode (em eRiverside See cig pe 52 Docsity.com  1950’s Now Population 4.8 Million 6 Million Vehicles 2.3 Million 11 Million Peak Ozone Levels 0.68 ppm 0.21 ppm Peak CO Levels 33 ppm 10 ppm Peak NO2 Levels 0.69 ppm 0.21 ppm Peak PM10 Levels 649 μg/m3 183 μg/m3 70% Reduction of most pollutants!!! How have we done? 55 Docsity.com Schedule for meeting Federal Standards: CO: 2000—Actually met in 2003 PM10: 2006 Ozone (1-hr): 2010 but we will not meet it PM2.5—2018 but it is unlikely we will meet it Ozone (8-hr)—2018 but it is unlikely we will meet it 56 Docsity.com 19 76 19 79 19 82 19 85 19 88 19 91 19 94 19 97 20 00 20 03 S ta ge 1 S M O G A LE R T 1- hr , 1 20 p pb 8- hr 8 5 pp b 0 50 100 150 200 250 D ay s E xc ee di ng S ta nd ar d Year 57 Docsity.com Human Hair (60 um diameter) Hair cross section (60 tm) an : PM190 PMO0.1 PM72.5 OCI Biri) Coe Lao aH) 60 Docsity.com  0.000 Aerosol Normal npurities ] aad Quiet Outdoor Air Fog Mist aindrop aah atic iP >< >< Metal Dust and Fume il > thinly Dust and Fume Sal Ammoniac Fume Molding Dust + > « > 7 Zine Dust Marble Grinding Alkah Fume le > Sulfurized Minerals T > Sulfuric Acid Mist a Cement Dust] ae Sulfide eus ck Condensed Zine Dust ceaala Dust Soot Aerosol Insecticide | Spores < >< ><+-> Bacteria| 5 < > Magnesium Oxide Smoke Flying Ash « itil > + Sand Gas Molecule E i Paine > ‘ namel Pain Silver Vein Particles Powdered Mite | TT <> Nuclear Burning Human Hair sak < Sea Salt < Visible Range ro 0.001 0.01 Oo. 1 10 100 1,000 10,000 ym 61 Docsity.com Mass Concentrations and Composition of Tropospheric Aerosols Percent Composition Region Mass (µg/m3) C(elem) C(org) NH+4 NO − 3 SO 2− 4 Remote 4.8 0.3 11 7 3 22 Non-urban Continental 15 5 24 11 4 37 Urban 32 9 31 8 6 28 Rubidoux, CA (1986 an- nual average) 87 3 18 6 20 6 1 62 Docsity.com Sources of Particulates • Abrasion and grinding: Grinding, abrasion or crushing produces road dust and construction dusts. ➔ “Fugitive” dusts • Combustion: As hot gasses cool, some have low enough volatility to condense and form particles. • Photochemistry: VOCs, NOx, and SO2 are oxidized to compounds that are sufficiently non-volatile that they condense out onto particles. 65 Docsity.com Aerosol Removal Processes • Diffusion—Brownian motion of molecules also applies to particles. This is inversely proportional to D or D2; the smaller the particle the larger the removal rate. ➔ Diffusion is completely negligible for particles larger than ~10 µm, and it is 106 times faster for 0.001 µm particle than a 2 µm particle. 66 Docsity.com • Gravitational Settling—speed of removal is proportional to D2; therefore more important for larger particles, and completely negligible for 0.01 µm particles. • The rate at which particles settle due to gravity is derived by balancing the gravitational pull with the frictional drag force provided by air: m = mass of particle (g) g = gravitational acceleration (9.80 m/s2) d = particle diameter (m) ρ = particle density (g/m3) η = viscosity of air (0.0172 g/ms) v = settling velocity (m/s) mg = π 6 d 3ρg = 3πηvd v = d 2ρg 18η 67 Docsity.com Small particles (less than 1 micron) undergo Brownian diffusion. The equation governing this process is given by: C: an empirical correction factor that takes care of the transition between when particles “see” a continuous fluid and when they experience the life of a billiard ball. The mean free path of air @ 1 atm, room temp is 0.07 µm. k = Boltzmann constant T = temperature (K) d = particle diameter (m) η = viscosity of air (0.0172 g/ms) D = diffusion coefficient C = Cunningham correction factor D = kTC 3πηd 70 Docsity.com Figure 5.8 Typical washout coefficients for rain scavenging and snow scavenging of particles. The daca for snow are shown as asterisks; all ocher data are for rain. Field data are given for a number of experiments by different research groups. Dashed lines through the rain data are provided to indicate trends in scavenging as a function of particle size. Washout coefficient (fractional decrease s~' ) 10 = Snow 0.01 O41 1 Aerodynamic diameter (4m) 10 71 Docsity.com This means that the particles that are between ~0.05 and 1 µm radius have the longest lifetime in the air. 72 Docsity.com Sinuses Adenoids Tonsils Tongue Pharynx ronchiole Epiglottis Larynx Smooth Trachea muscle Esophagus Right bronchus i Terminal px bronchiole Alveolus Mucus-producing goblet cells Mucus Columnar cells Alveolar sacs (b) Basement membrane ite Bronchial lining Connective tissue (epithelium) (a) FIGURE 7.9 The human respiratory system. (a) The system as a whole and a cross-section of the bronchial lining showing the cilia, and (b) details of the lower respiratory system terminating in the alveoli. (Source: Williamson, 1973.) 75 Docsity.com  causes of death and illness in adults and children 25 T | (Cl =2004) __ | | O Mlehoden Syrpturaiearcdies eh rate chide | 2 36-5 a Peg enepiea ents 55% | z carrie 459 level t 2 g a *4 - = 7 j | : HI. 7 | ht, i} | ij | a r T k Plies chat Hig. EEE EE gt Tl I | Adults | Chiltran O85 I | oT TT at 129495 12945 12345 BF HOW WABI 181617 | 16 teIT Ie WE ABT IO ‘Tata! Resoialoy (Cerdinescular «= Respimtoy = COPD er IHD = Cough Lower Upper invewtalehy mately morale hospihal hospital WREDIaNON — rietpimtocy acimisaions admission aymalcms = syraplems Source: EPA, 1996, hased on 18 studies 76 Docsity.com