1. Lab report from each person, not 1 per group. 2. Progress on Lab 5, particle composition? Lab 5 due April Lab 6 due April 20.

Transcription

1 1. Lab report from each person, not 1 per group. 2. Progress on Lab 5, particle composition? Lab 5 due April Lab 6 due April 20.

2 LAB 6: Ozone/NOx Source of Ozone Volatile Organic Compounds (VOCs) + Nitrogen Oxides (NOx) Ozone (O 3 ) + OVOCs Fuels, Vegetation & Paints, Solvents Combustion Processes

3 Sources of Tropospheric O 3 and NO x Ozone is formed through: O + O 2 + M O 3 + M; both in the stratosphere and troposphere - Natural sources: from hydrocarbons (VOCs, eg, RH) released from plants, soils... and from strat. - Anthropogenic sources: emissions of RH and NOx produce ozone smog. NOx (= NO+NO 2 ) Global emissions Fossil fuel combustion 45% Biomass burning 15 Lightning 9 Soil release (natural and anthro.) 23 Largely NO formed by reactions of N 2 and O 2 at high T

4 Formation of Ozone: The Photostationary State NO 2 + hv --> NO + O; rate: k 1 = j NO2 (s -1 ) (photolysis rate) O + O 2 + M --> O 3 + M; k 2, fast (only source of atm O 3 ) O 3 + NO --> NO 2 + O 2 ; k 3 Consider only these three reactions take place: - No net O 3 production - Solve equations assuming [O] is constant (reacts fast: psuedo-steady-state-approx.): [O 3 ] pss = k 1 [NO 2 ]/k 3 [NO] (photostationary state) Solve for k 1, or j NO2 (photolysis rate) j NO2 = k 3 [O 3 ][NO]/[NO 2 ]

5 Formation of Ozone in Polluted Areas NO 2 + hv --> NO + O O + O 2 + M --> O 3 + M O 3 + NO --> NO 2 + O 2 But other species generate NO 2 and consume NO shifting pss RH + OH + O 2 --> RO 2 + H 2 O RO 2 + NO RO + O 2 --> RO +NO 2 --> RCHO + HO 2 HO 2 + NO --> OH + NO 2 Organic compounds (VOCs) produce radicals that lead to NO 2 production and consume NO.

6 O 3 Formation, Transport and influences on PM O 2 O 3 hv Fine PM, SOA Wind PM, SO 2, NO x Emissions NO NO 2 OH HNO 3 OH RO 2 /HO 2 RO,OH VOC Emissions Deposition Rainout O 3, HNO 3 PM

7 Ozone Isopleths Area of effective VOC control (most often highly populated areas)# Nitrogen Oxides (NO x )! Constant [O 3 ]# NOx control effective (areas with high biogenics)! High [O 3 ] # Low [O 3 ] # Volatile Organic Compounds (VOC)!

8 Ozone: A Criteria Pollutant Regulated by EPA Carbon monoxide (CO) Sulfur dioxide (SO 2 ) Nitrogen dioxide (NO 2 ) Particulate matter (PM) Ozone (O 3 ) Lead (Pb) Air toxics (solvents, fuels, metals, etc.) Haze criteria pollutants EPA must describe the characteristics and potential health and welfare effects of these pollutants

9 National Ambient Air Quality Standards Primary Standards: protect public health (sensitive populations) Secondary Standards: protect public welfare (visibility, crops ) Ozone: (primary & secondary) ppm (8hr avg) NO 2 : prim. 100 ppb (1hr avg); sec. 53 ppb (annual)

10 Ozone and Human Health Evidence of health impact of ozone on human respiratory system based on an experimental study involving human subjects. Left: A healthy lung airway, and right: A lung airway inflamed from exposure to ozone. Ozone and Your Health. EPA 452/F Office of Air and Radiation, U.S. EPA:

11 Ozone and Ecological Health Cotton showing chronic response to ozone on the lower leaves after exposure to rel. low concentrations (e.g. < 40 ppb), with periodic, random, intermittent episodes of rel. high ozone concentrations (e.g. > 80 ppb) throughout the plant growth season. Krupa, S.V., A.E.G. Tonneijck, and W.J. Manning Ozone. Pp in Recognition of Air Pollution Injury to Vegetation: A Pictorial Atlas, 2nd Ed, R.B. Flagler, et al., eds. Pittsburgh, PA: Air & Waste Management Association.

12 Thermo Environmental Inst. 49C Based on O 3 absorption at 254nm Beer s Law I = I 0 e -ε c l ε = 308 cm -1 (@STP: 0 o C, 760Torr) l = 38 cm L: path length ε: absorption coef, or cross-section C: concentration

13 O 3 Method: UV Absorption 254 nm Why two cells and why switch back and forth?

14 O 3 Primary Standard Calibrator I = I 0 e -ε c l ε = 308 cm -1 (@STP: 0 o C, 760Torr) l = 38 cm [O 3 ] nomc Zero Air

15 Teledyne API NOx Analyzer Measurement of NO NO + O 3 NO 2 * + O 2 NO 2 * NO 2 + hv -Operating Principle- Measurement of NO 2 (and other things) using a heated molybdenum converter (Mo at 315 C) 3NO 2 + Mo 3NO + MoO 3 Ie, converts all NOx (NO+NO 2 +any other NO) to NO and measures as above. NO 2 = NOx - NO

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17 Lab Goals Calibrate O 3 & NOx analyzers and determine: DL, consider measurement uncertainty. Sample O 3 and NO x (NO, NOx NO 2 ) for 24 hours along with met data. Discuss sources of measurement uncertainty, explain measured diurnal profiles of O 3, NO, NO 2, jno 2 and compare to expected values. TA: Laura King lauraking@gmail.com Lab will be available this Wed. April 4 through Friday April 13.