Air Pollution Chapter 12 What s in the air O3 NO NO2 CO CO2 SO2 HCHO And other things like particulates and Black Carbon Types and Sources of Pollutants primary and secondary pollutants Gases and particulate matter Gases Carbon monoxide Sulfur Dioxide Nitric Oxide Nitrogen Dioxide Particulates are classified by size PM10 PM2 5 diameter size in microns 2 5 m Pollutants can be classified as primary pollutants and secondary pollutants Primary Pollutants Carbon Monoxide CO is a tasteless colorless and odorless gas Sources of CO include fossil fuel combustion Incomplete combustion in autos trucks and airplanes some industrial process biomass burning and photolysis reactions Concentrations of CO in urban air are typically 2 10 ppmv On freeways and in traffic tunnels values rise to more than 100 ppmv Primary Pollutants Sulfur Dioxide SO2 is a colorless gas that exhibits a taste at levels of 0 3 ppmv and a strong odor at levels greater than 0 5 ppmv Sources of SO2 include coal fired power plants automobile tailpipes and volcanoes Background concentrations in the troposphere range from 10 pptv to 1 ppbv In polluted air 1 30 ppbv Primary Pollutants Nitrogen oxides are gases that form when some of the nitrogen in the air reacts with oxygen during the high temperature combustion of fuel Nitric Oxide NO is a colorless gas and a free radical Precursor to tropospheric ozone Sources include fossil fuel combustion autos and planes and biomass burning Nitrogen Dioxide NO2 is a brown gas with a strong odor Absorbs short wavelengths Intermediary between NO and O3 production Primary Pollutants Background concentrations range from 20 to 50 pptv In urban areas concentrations are 0 1 0 25 ppmv In midmorning NO2 is more prevalent than during midday because sunlight breaks down most NO2 past midmorning NOx NO NO2 Primary Pollutants Volatile organic compounds VOCs represent a class of organic compounds that are mostly hydrocarbons individual organic compounds composed of hydrogen and carbon Methane naturally occurring is the most abundant Others include benzene formaldehyde HCHO Secondary Pollutants Secondary pollutants form chemically in the air Ozone is a secondary pollutant in the troposphere Ozone O3 is a relatively colorless gas Ozone exhibits an odor at concentrations of 0 02 ppmv or greater Ozone has a sweet smell Copy machine Ozone is not emitted Background concentrations in troposphere are 20 to 40 ppbv In urban air concentrations range from 0 01 ppmv at night to 0 5 ppm during afternoons in the most polluted cities Typical mixing ratios are 80 100 ppb in urban air In 2008 EPA lowered the 8 hr primary standard from 84 ppbv to 75 ppbv Chemistry of Photochemical Smog Photochemical smog involves reactions among NOx and VOCs in the presence of sunlight On a typical day ozone forms following emission of NO and VOCs In polluted air ozone production occurs along the following lines Sunlight dissociates NO2 into NO and atomic oxygen NO2 solar radiation NO O The atomic oxygen combines with molecular oxygen in presence of a third molecule M to form ozone as O O2 M O3 M The ozone is then destroyed by combining with nitric oxide thus NO O3 NO2 O2 Chemistry of Photochemical Smog NO O3 NO2 O2 If sunlight is present the newly formed NO2 will break down into NO and atomic oxygen The atomic oxygen then combines with molecular oxygen to form ozone again Large concentrations of O3 can form in polluted air only if some of the NO reacts with other gases without removing ozone in the process Chemistry of Photochemical Smog EPA Standards National Ambient Air Quality Standards NAAQS 75 ppb O3 for an 8 hour averaging period 120 ppb O3 for a 1 hour averaging period The number of unhealthy days during 2003 Fig 12 11 p 338 The days exceeding 1 hr standard in LA Air Quality Index AQI Particulate Matter Particulate Matter PM represents a group of solid particles and liquid droplets that are small enough to remain suspended in the air Collectively known as aerosols this grouping includes solid particles that may irritate people but are usually not poisonous These include soot dust smoke and pollen Some more dangerous substances include asbestos fibers and arsenic Particulates are classified by size PM10 PM2 5 diameter size in microns 2 5 m Black Carbon Black Carbon is a primary aerosol component of Diesel Particulate Matter a known toxin and regulated pollutant by several regulatory agencies including the California Air Resources Board CARB Diesel Particulate Matter is known to cause adverse health effects in people who are exposed including premature hospitalization asthma attacks bronchitis other respiratory and cardiovascular symptoms and premature death Black Carbon is the second leading cause of Global Warming Black Carbon is emitted as a primary pollutant to the atmosphere through a variety of incomplete combustion of sources and fuels BC concentration cannot be modeled or predicted it must be measured Black Carbon is NOT adequately characterized through PM 2 5 mass only measurements chemical speciation is necessary Magee Scientific Black Carbon Aerosol black carbon BC is a particulate pollutant species emitted from the combustion of any carbonaceous fuel The name Aethalometer is derived from the classical Greek verb aethaloun meaning to blacken with soot It is this optically absorbing material that the standard Aethalometer measures The only known source of aerosol black carbon in the atmosphere is the combustion of carbonaceous fuels There are no known significant biological geological or meteorological sources Factors that Affect Air Pollution The Role of the Wind Dilution Turbulence Mixing Dilution is the solution to pollution in the 1950s this motto led to the construction of tall smokestacks for large factories Pollution was released higher in the atmosphere where winds were stronger Air quality improved locally but suffered downwind Atmospheric stability determines where pollutants get transported The Role of Stability and Inversions temperature lapse rates inversions mixing depth The mixing layer can often be easily seen from an airplane The Role of Atmospheric Stability The Role of Topography cold air drainage air blockage by mountain ranges Severe Air Pollution Potential sources high pressure inversions stagnation Some locations like Los Angeles and Mexico City have an unfortunate combination of surrounding topography frequent inversions abundant emissions and plentiful sunlight perfect conditions for