1. Introduction to Air Quality Monitoring Systems Topics to be covered: 1.Basic urban air quality 2.Measurements of ozone 3.Measuring NO x 4.Measuring Black Carbon 5.Issues with monitoring systems Met 163 7 May 2009

2. What is in Urban Air? O 3, NO, NO 2, CO, CO 2, SO 2, HCHO And other things like particulates and Black Carbon!

3. Primary Pollutants Carbon Monoxide (CO): is a tastless, 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.

4. Primary Pollutants Sulfur Dioxide (SO 2 ): 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 SO 2 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.

5. Primary Pollutants 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 (NO 2 ): is a brown gas with a strong odor. Absorbs short wavelengths. Intermediary between NO and O 3 production.

6. Primary Pollutants Background concentrations range from 20 to 50 pptv. In urban areas, concentrations are 0.1-0.25 ppmv. In midmorning NO 2 is more prevalent than during midday because sunlight breaks down most NO 2 past midmorning. NO x = NO + NO 2

7. Secondary Pollutants Secondary pollutants form chemically in the air. Ozone is a secondary pollutant in the troposphere. Ozone (O 3 ): 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.

8. Chemistry of Photochemical Smog Photochemical smog involves reactions among NOx and reactive organic gases (ROGs) in the presence of sunlight. We call ROGs volatile organic compounds (VOCs) which are emitted from cars and processing industry. On a typical day, ozone forms following emission of NO and ROGs. ROGs are broken down chemically into peroxy radicals, RO 2. NO + RO 2 NO 2 + RO NO + O 3 NO 2 + O 2 O + O 2 O3O3 NO 2 + hν NO + O

9. EPA Standards National Ambient Air Quality Standards (NAAQS) 75 ppb O 3 for an 8-hour averaging period 120 ppb O 3 for a 1-hour averaging period

10. Gas Absorption: absorption occurs when radiative energy enters a substance and is converted to internal energy, increasing the temperature of the substance. Absorption removes energy from an incident beam, reducing the amount of radiation received past the point of absorption. Gases selectively absorb radiation in different portions of the electromagnetic spectrum. Ozone absorbs UV radiation at wavelengths < 0.35 μm and between 0.45-0.75 μm.

11. Monitor Labs 9810B Ozone Analyzer

12. Description UltraViolet Photometer Model: 9810b Released in 1996 by Monitor Labs, Inc. Now owned by Teledyne Monitor Labs http://www.teledyne-ml.com/

13. Technology Nondispersive UV photometer alternately switches a ozone scrubber in and out of measuring stream. Scrubber uses manganese dioxide (MnO 2 ) to destroy only the ozone and pass other common absorbers (SO 2, etc). Mercury vapor lamp as the light source with 254 nm at the center of absorption band. Transmitted light density computes ratio of ozone scrubbed air (ozone free air) to non-scrubbed air (ozone air). Has a microprocessor to monitor and adjust temperature and pressure.

14. Pneumatics Flow Rate = 0.5 slpm Ozone Scrubber Measurement Valve Measurement cell absorption External Pump Sample Flow control UV lamp source Outlet Span Port Zero Port DFU Ozone Cell with UV lamp Zero air scrubber Internal zero span module Inlet

15. Technology Measurement Cell: –Mercury vapor lamp as source –vacuum photodiode as detector A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.photodetectorlightcurrentvoltage –Glass tube used as absorption cell Reference cycle: ozone is scrubbed out of sample and light intensity is determined (I o ) Sample cycle: light intensity is determined for ambient air with ozone (I).

16. Technology Beer/Lambert Law gives ozone concentration: O 3 = O 3 concentration, ppm a = absorption coefficient of O 3 at 245 nm=308 atm -1 cm -1 at 0˚C and 760 torr (760 torr=101kPa) l = optical path length, cm T = sample temperature, ˚K P = sample pressure, torr L = correction factor for O 3 losses

17. Measuring NO x

18. Theory of Operation Gas-phase Chemiluminescence detection to analyze nitric oxide (NO), total oxides of nitrogen (NO X ), and nitrogen dioxide (NO 2 ) Instrument has a pneumatic system, an NO 2 -to-NO converter, a reaction cell, detector (PMT), and processing electronics

19. Theory of Operation The luminescence from an activated molecular NO 2 species produced by the reaction between NO and O 3 : NO + O 3 → NO 2 + O 2 As the activated species NO 2 reverts to a lower energy state, it emits broad-band radiation from 500-3000 nm. NO concentration is proportional to the intensity of the chemiluminescent →proportional to the current output.

20. Parts diagram FRONT DELAY COIL POWER SUPPLY PERMAPURE DRYER OZONE GENERATOR MOLYCON Catalytic converter VALVE MANIFOLD OPTICAL BENCH FAN REACTION CELL VOLTAGEREGULATOR BOARD MICROPROCESSOR BOARD NOx PRE-PROCESSOR BOARD FRONTREAR

21. Air flow diagram EXTERNAL PUMP EXHAUST PARTICULATE FILTER SAMPLE PORT EXHAUST PORT DELAY COIL REACTION CELL ASSY NO 2 hn OPTICAL BENCH ASSY VALVE MANIFOLD NO2 → NO CONVERTER MOLYCON ASSY DRYER ASSY OZONE GENERATOR AIR INTAKE NO2

22. Calibration process The analyzer must be calibrated initially and periodically to determine the reliability and accuracy of all air quality data. Single/multi point calibration: calibrated against know sources of NO and NO 2 (NIST standards etc.) 1.Establish a reliable and stable calibrating source. 2.Calibrate the analyzer against the calibrating source. Zero/span calibration

23. 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

24. 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’, (αεφαλουν) 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. Black Carbon

25. The optical method that we use is a measurement of the attenuation of a beam of light transmitted through the sample when collected on a fibrous filter. When calculated as shown, this quantity is linearly proportional to the amount of BC in the filter deposit. Define I 0 as the intensity of light transmitted through the original filter, or through a blank portion of the filter. Define I as the intensity of light transmitted through the portion of the filter on which the aerosol deposit is collected. The ‘Optical Attenuation’ ATN is defined as ATN = 100 * ln (I 0 / I ) The Aethalometer: The Optical Attenuation Method

26. This measurement is affected by the wavelength of the light with which it is made, provided that the particle size is somewhat smaller than the wavelength. The absorption of light by a broad band absorber such as graphitic carbon is inversely proportional to the wavelength of the light used. Thus, for a given mass of black carbon [BC], the optical attenuation at a fixed wavelength λ may be written as ATN(λ) = σ (1/λ) * [BC] The Aethalometer model AE-16 uses a solid-state source operating in the near-infrared at a wavelength of 880 nm. The Aethalometer: The Optical Attenuation Method where [BC] is the mass of black carbon, and σ (1/λ) is the optical absorption cross-section (‘sigma’) that is wavelength dependent, and which is referred to as the ‘Specific Attenuation’.

27. Range- the measurand interval over which a sensor is designed to respond. Span- the algebraic difference between the upper and lower range values. Resolution- the smallest change in the primary input that produces a detectable change in the output. Hysteresis- is present when the sensor output for a given input depends upon whether the input was increasing or decreasing. Imprecision or uncertainty- is a measure of the noise or scatter in the measurement. Bias- is the systematic error. The purpose of static calibration is to remove the bias and to numerically define the imprecision. Definitions