Nitrogen Compounds in the Atmospheric Chemistry Division Lecture

Nitrogen Compounds in the Atmospheric Chemistry Division Lecture Series 2011 8 March 2011 Frank Flocke ACD FFL@ucar. edu 1

Nitrogen “Families” • N 2 O • • NOx (NO + NO 2) N 2 O 5 HNO 3 (HONO 2) HONO HOONO 2 PANs (RC(O)OONO 2) Alkyl Nitrates (RONO 2) XONO 2 (X = halogen) “NOy” • NO 3 radical • NO 3 - nitrate aerosol 8 March 2011 Frank Flocke ACD FFL@ucar. edu 2

N 2 • Nitro – gen (found in HNO 3 in the 18 th century) • Azotos – “lifeless gas” • Stickstoff – “asphyxiating substance” • Extremely stable, bond energy 945 k. J/mol 8 March 2011 Frank Flocke ACD FFL@ucar. edu 3

N 2 O • Greenhouse gas • 40/60 anthro/bio sources • Increase of ~20% due to anthropogenic emissions • 120 year atmospheric lifetime • stratospheric NOx source 8 March 2011 Frank Flocke ACD FFL@ucar. edu Ledley et al, 1999 4

Stratospheric NOx Chemistry N 2 O + O(1 D) 2 NO N 2 + O 2 O 3 + hv N 2 O + hv O 2 + O(1 D) N 2 + O(1 D) Catalytic Ozone destruction Cycle (Stratosphere): NO + O 3 NO 2 + O 2 NO 2 + O NO + O 2 O + O 3 2 O 2 8 March 2011 (~60%) (~40%) “null cycle” Stratosphere + Troposphere: NO + O 3 NO 2 + O 2 NO 2 + hv NO + O O 3 O + O 2 Frank Flocke ACD FFL@ucar. edu 5

Stratospheric NOx Chemistry Catalytic Ozone destruction cycles (Stratosphere): NO + O 3 NO 2 + O 2 Cl + O 3 Cl. O + O 2 NO 2 + O NO + O 2 Cl. O + O Cl + O 2 O + O 3 2 O 2 But… Cl. O + NO 2 Cl. ONO 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 6

Ozone “hole” chemistry Lower Stratosphere “denitrified” and chlorine activated Cl. ONO 2 + HCl(s) Cl. ONO 2 + H 2 O(s) N 2 O 5 + HCl(s) N 2 O 5 + H 2 O(s) Cl 2 + HNO 3(s) HOCl + HNO 3(s) Cl. NO 2 + HNO 3(s) 2 HNO 3(s) Cl + O 3 Cl. O + O 2 Cl + O 2 O + O 3 2 O 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 7

8 March 2011 Frank Flocke ACD FFL@ucar. edu 8

Ozone “hole” chemistry Lower Stratosphere “denitrified” and chlorine activated Cl. ONO 2 + HCl(s) Cl. ONO 2 + H 2 O(s) N 2 O 5 + HCl(s) N 2 O 5 + H 2 O(s) Cl 2 + HNO 3(s) HOCl + HNO 3(s) Cl. NO 2 + HNO 3(s) 2 HNO 3(s) Cl + O 3 Cl. O + O 2 Cl + O 2 Pinatubo eruption, 1991, Photo: USGS O + O 3 2 O 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 9

Tropospheric Reactive Nitrogen 8 March 2011 Frank Flocke ACD FFL@ucar. edu 10

Tropospheric Reactive Nitrogen • • NOx (NO + NO 2) N 2 O 5 HNO 3 (HONO 2) HONO HOONO 2 PANs (RC(O)OONO 2) Alkyl Nitrates (RONO 2) XONO 2 (X = halogen) NOz = NOy-NOx NOy reservoir species NOy, or odd nitrogen • NO 3 radical • NO 3 - nitrate aerosol • NH 3, Amines 8 March 2011 Frank Flocke ACD FFL@ucar. edu 11

Tropospheric Reactive Nitrogen • • NOx (NO + NO 2) N 2 O 5 HNO 3 (HONO 2) HONO HOONO 2 PANs (RC(O)OONO 2) Alkyl Nitrates (RONO 2) XONO 2 (X = halogen) NOz = NOy-NOx NOy reservoir species • NO 3 radical • NO 3 - nitrate aerosol Sources of reactive Nitrogen • NH 3, Amines 8 March 2011 NOy, or odd nitrogen Frank Flocke ACD FFL@ucar. edu 12

Combustion source for NOx • No nitrogen in fuel N 2 + O = NO + N +314 k. J/mol N + O 2 = NO + O N + OH = NO + H (not important) Alentec Inc. • Nitrogen in Fuel HCN(g), RCN(g), NH 3, etc + OH/O NOx 8 March 2011 Frank Flocke ACD FFL@ucar. edu 13

NOx emission sources NOx + VOC + O 3 NOx + VOCs cities (transportation) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 14

NOx emission sources NOx + VOC + O 3 NOx + VOCs Cities (transportation) VOCs NOx Forests power plants NOx + VOCs Industry Soils and Agriculture 8 March 2011 Frank Flocke ACD FFL@ucar. edu 15

NOx emission sources Lightning NOx + VOC + O 3 NOx + VOC cities (transportation) VOC forests NOx power plants NOx + VOC NO +VOC x industry Soils and fires Agriculture 8 March 2011 Frank Flocke ACD FFL@ucar. edu 16

Sources of U. S. NOx and VOC Emissions VOCs NOx Other 10% Non-Road Engines 18% Non-Road Other Engines 7% 5% Natural 6% On-Road Vehicles 11% Electric Utility 24% Solvent Use 13% On-Road Vehicles 29% Industrial 13% Natural 61% Industrial 3% Source: EPA 8 March 2011 Frank Flocke ACD FFL@ucar. edu 17

Global Budget of NOx in the Troposphere (Tg N/yr) 80 s-90 s Sources/Production Fossil fuel combustion Biomass burning Soil emission Lightning NH 3 oxidation Ocean emission Aircraft Stratospheric input Total Sinks Wet deposition Dry deposition Total 8 March 2011 Ehhalt and Drummond (1982) (1983) Logan (1991) Sanhueza 13. 5 (8. 2 -18. 5) 11. 5 (5. 6 -16. 4) 5. 5 (1 -10) 5. 0 (2 -8) 3. 1 (1. 2 -4. 9) 0. 3 (0. 2 -0. 4) 0. 6 (0. 3 -0. 9) 21. 0 (14 -28) 12. 0 (4 -24) 8. 0 (4 -16) 8 (2 -20) ? (0 -10) 1 0. 5 21 2. 5 -8. 5 10 -20 2 -8 0. 6 1 39 (19 -59) 50. 5 (25 -99) 37 -59 24 (15 -33) - 27 (12 -42) 16 (11 -22) - 24 (15 -33) 43 (23 -64) - Frank Flocke ACD FFL@ucar. edu 18

8 March 2011 Frank Flocke ACD FFL@ucar. edu 19

Modeled NOx near surface (1990 s) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 20

IPCC AR 4 NOx in the troposphere (2000) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 21

SCIAMACHY global mean NO 2 (2004) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 22

Developments in Asia 1000 cars / day are added to the Beijing road system 8 March 2011 (Steve Massie) China GDP and NO 2 trends ~ 10 % / year Frank Flocke ACD FFL@ucar. edu 23

NOx emissions … a moving target 8 March 2011 Frank Flocke ACD FFL@ucar. edu 24

NOx emissions http: //www. iiasa. ac. at/webapps/tnt/Rcp. Db/dsd? Action=htmlpage&page=c ompare 8 March 2011 Frank Flocke ACD FFL@ucar. edu 25

NOx chemistry in the troposphere NOx is synonymous with “photochemical smog” or ozone photochemistry 8 March 2011 Frank Flocke ACD FFL@ucar. edu 26

NOx chemistry in the troposphere 8 March 2011 Frank Flocke ACD FFL@ucar. edu 27

NOx chemistry in the troposphere 8 March 2011 Frank Flocke ACD FFL@ucar. edu 28

NOx chemistry in the troposphere 8 March 2011 Frank Flocke ACD FFL@ucar. edu 29

Photochemical Smog – 1950’s Arie-Jan Haagen-Smit: “Ozone from smog and sunlight” 8 March 2011 Frank Flocke ACD FFL@ucar. edu 30

Photochemical Smog – 1950’s Edgar Stephens, et al, 1956: Discovery of PAN (“compound X”) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 31

Photochemical Smog – 1950’s Edgar Stephens, et al, 1956: Discovery of PAN (the first NOx reservoir species) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 32

Photochemical processes involving NOx Leighton, 1961: “O 3 and NOx live in photostationary state” 8 March 2011 Frank Flocke ACD FFL@ucar. edu 33

NOx photostationary state O 3 + NO 2 + O 2 NO 2 + hv NO + O 2 + M O 3 + M ___________ Null t ≈ 100 seconds [NO]/[NO 2] = k[O 3] / JNO 2 P(O 3) = 0 Ox = O 3 + NO 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 34

Photochemical processes and tropospheric ozone formation • Leighton, 1961: O 3 and NOx (NO+NO 2) live in a “photostationary state” • H. Levy, 1972: OH radical oxidizes CO, CH 4, VOC • P. Crutzen et al. , W. Chameides et al. , J. Logan et al. late 70’s: HOx and NOx cycles responsible for ozone production in the troposphere 8 March 2011 Frank Flocke ACD FFL@ucar. edu 35

Role of NOx in ozone production OH + CO 2 + H H + O 2 +M HO 2 + M HO 2 + NO 2 + OH NO 2 + hv NO + O 2 + M O 3 + M ___________ CO + 2 O 2 +hv CO 2 + O 3 OH + CH 4 +O 2 CH 3 O 2 + H 2 O CH 3 O 2 + NO 2 + CH 3 O + O 2 HO 2 + CH 2 O 8 March 2011 Frank Flocke ACD FFL@ucar. edu 36

Role of NOx in ozone production HO 2 + NO 2 + OH CH 3 O 2 + NO 2 + CH 3 O + O 2 HO 2 + CH 2 O NO 2 + hv NO + O 2 + M O 3 + M O 3 + NO 2 + O 2 k’ k” k P(O 3) = [NO] * (k’[HO 2] + k”[CH 3 O 2]) [NO]/[NO 2] = (k[O 3] + k’[HO 2] + k”[CH 3 O 2]) / JNO 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 37

8 March 2011 Frank Flocke ACD FFL@ucar. edu 38

8 March 2011 Frank Flocke ACD FFL@ucar. edu 39

8 March 2011 Frank Flocke ACD FFL@ucar. edu 40

Near-Zero NOx troposphere OH + CO 2 + H H + O 2 +M HO 2 + M HO 2 + O 3 2 O 2 + OH HO + O 3 O 2 + HO 2 __________ CO + O 3 CO 2 + O 2 O 3 + hv O(1 D) + O 2 O(1 D) + M O + M O(1 D) + H 2 O 2 OH 8 March 2011 Frank Flocke ACD FFL@ucar. edu k l” k l’ JO 1 D f 41

Ozone production and loss P(O 3) = [NO] * (k’[HO 2] + k”[CH 3 O 2]) L(O 3) = [O 3] * (kl’[OH] + kl”[HO 2] + f JO 1 D) P(O 3) = L(O 3) [O 3] * (kl’[OH] + kl”[HO 2] + f JO 1 D) NO’ = k’[HO 2] + k”[CH 3 O 2] 8 March 2011 Frank Flocke ACD FFL@ucar. edu 42

Mauna Loa Hawaii 8 March 2011 Frank Flocke ACD FFL@ucar. edu 43

Mauna Loa Hawaii 8 March 2011 Frank Flocke ACD FFL@ucar. edu 44

Mauna Loa Hawaii 8 March 2011 Frank Flocke ACD FFL@ucar. edu 45

Ozone budget: Box model simulations Profiles of NO and net O 3 production rates during PEM-WEST B, 1994 Separation into two distinct air mass types (high NOx and low NOx) [Crawford et al. , JGR 102, 1997] NO profiles 8 March 2011 Net P(O 3) profiles Frank Flocke ACD FFL@ucar. edu 46

Near-Zero NOx troposphere OH + CO 2 + H H + O 2 +M HO 2 + M HO 2 + O 3 2 O 2 + OH HO + O 3 O 2 + HO 2 __________ CO + O 3 CO 2 + O 2 HO 2 + HO 2 H 2 O 2 HO 2 + HO H 2 O + O 2 H 2 O 2+hv 2 OH H 2 O 2 + H 2 O(liq) H 2 O 2(liq) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 47

Back to the role of NOx in the chemistry of the troposphere 8 March 2011 Frank Flocke ACD FFL@ucar. edu 48

Does NOx cycle around forever? HO 2 + NO 2 + OH CH 3 O 2 + NO 2 + CH 3 O + O 2 HO 2 + CH 2 O NO 2 + hv NO + O 2 + M O 3 + M O 3 + NO 2 + O 2 k’ k” k P(O 3) = [NO] * (k’[HO 2] + k”[CH 3 O 2]) [NO]/[NO 2] = (k[O 3] + k’[HO 2] + k”[CH 3 O 2]) / JNO 2 8 March 2011 Frank Flocke ACD FFL@ucar. edu 49

NOx loss reactions (remote trop) NO 2 + OH + M HNO 3 + M kn NOx lifetime: τ(NOx) = τ(NO 2) (1+[NO]/[NO 2]) Catalytic efficiency: CE ≈ P(O 3) / L(NOx) CO cycle only: CE ≈ k’[NO][HO 2] / kn[OH][NO 2] 8 March 2011 Frank Flocke ACD FFL@ucar. edu 50

NOx influence on HOx partitioning 8 March 2011 Frank Flocke ACD FFL@ucar. edu 51

Problems 1. Calculate the “critical NO” (P(O 3) = L(O 3)) for the following conditions: – – – Surface, t=298 K, [HO 2] = 40 ppt, [CH 3 O 2] = 25 ppt, [O 3] = 40 ppb, [OH] = 1 x 106; f = 0. 15; J(O 1 D) = 2. 5 x 10 -5 k’=k”= 8. 5 x 10 -12 cm 3 molecule-1 s-1 kl’= 7. 3 x 10 -14 cm 3 molecule-1 s-1; kl”= 2 x 10 -15 cm 3 molecule-1 s-1 2. Which of these reactions are the most important? 3. Calculate the lifetime of NOx at the surface and at 10 km altitude, considering only losses to HNO 3 1. 2. 3. 4. [OH] = 1 x 106, J(NO 2)=1 x 10 -2; consider alt-independent [O 3] = 40 ppb / 100 ppb; T=298 K / 220 K at surf/10 km, resp. k = 1. 4 x 10 -12 exp(-1310/T) cm 3 molecule-1 s-1 kn = 3. 3 x 10 -30 (T/300)-3. 0 [N 2] cm 3 molecule-1 s-1 4. What are the [NO]/NO 2] ratios at 0 and 10 km? 8 March 2011 Frank Flocke ACD FFL@ucar. edu 52

Beyond the remote troposphere Addition of a reactive hydrocarbon (isoprene): • Enhances [HOx] • Shifts O 3 production peak to larger NOx values • Still eventually turns over at high NOx 8 March 2011 Frank Flocke ACD FFL@ucar. edu 53

NOy: nitrogen “reservoir” species NO 2 + OH + M HNO 3 + M NO 2 + RO 2 + M ROONO 2 + M NO 2 + RC(O)O 2 + M RC(O)OONO 2 + M NO + RO 2 + M RONO 2 + M (0 -30%) RONO 2 + hv RO + NO 2 NO + OH + M HONO + M NO 2 + O 3 NO 3 + O 2 NO 3 + NO 2 + M N 2 O 5 + M NO 2 + H 2 Oliq HONOg + HNO 3 liq 8 March 2011 Frank Flocke ACD FFL@ucar. edu 54

NOx catalytic efficiency CE ≈ P(O 3) / L(NOx) [NO]{k’[HO 2] + Σ (k’i[RO 2]i)} CE ≈ kn[OH][NO 2]+km[NO 2][RC(O)O 2] +. . …. or determine it experimentally CE ≈ P(O 3) / P(NOy-NOx) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 55

A day in NOx city O 3 100 75 50 8 March 2011 Frank Flocke ACD FFL@ucar. edu 56

Experimental determination of CE 8 March 2011 Frank Flocke ACD FFL@ucar. edu 57

NOy: nitrogen “reservoir” species NO 2 + OH + M HNO 3 + M NO 2 + RO 2 + M ROONO 2 + M NO 2 + RC(O)O 2 + M RC(O)OONO 2 + M NO + RO 2 + M RONO 2 + M (0 -30%) RONO 2 + hv RO + NO 2 NO + OH + M HONO + M NO 2 + O 3 NO 3 + O 2 NO 3 + NO 2 + M N 2 O 5 + M NO 2 + H 2 Oliq HONOg + HNO 3 liq 8 March 2011 Frank Flocke ACD FFL@ucar. edu 58

HONO and Cl. NO 2 NO + OH + M HONO + M NO 2 + H 2 Oliq HONOg + HNO 3 liq N 2 O 5 + Na. Clliq Na. NO 3(liq) + Cl. NO 2 HONO + hv OH + NO Cl. NO 2 + hv Cl + NO 2 Early morning sources of radicals 8 March 2011 Frank Flocke ACD FFL@ucar. edu 59

Organic Nitrates Peroxy nitrates NO 2 + RO 2 + M ROONO 2 + M Alkyl nitrates NO + RO 2 + M RONO 2 + M (0 -30%) NO + RO 2 NO 2 + RO (70 -100%) Peroxy Acyl Nitrates (PANs) NO 2 + RC(O)O 2 + M RC(O)OONO 2 + M 8 March 2011 Frank Flocke ACD FFL@ucar. edu 60

Alkyl nitrates NO + RO 2 + M RONO 2 + M (α) NO + RO 2 NO 2 + RO (1 -α) − k [NO][RO ] P(O 3) = (1 -α) 2 α− ≈ 0. 05 -0. 08 − RONO 2 + hv RO + NO 2 RONO 2 dry deposition 8 March 2011 Frank Flocke ACD FFL@ucar. edu 61

Peroxyacyl nitrates (PANs) NO 2 + RC(O)O 2 + M RC(O)OONO 2 + M Equilibrium is strongly temperature dependent NO + RC(O)O 2 NO 2 + CO 2 + RO 2 In very cold environments / lower stratosphere: RC(O)OONO 2 + hv RC(O)O + NO 2 RC(O)OONO 2 + OH products (NO 2) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 62

O PAN CH 3 – C O – NO 2 Peroxyacetyl nitrate (Peroxyacetic nitric anhydride) CH 3 – CH 3 Ethane 8 March 2011 PAN structure Frank Flocke ACD FFL@ucar. edu 63

Strongly temperature dependent equilibrium O CH 3 – C • + O 2 O CH 3 – C O + NO 2 O–O • peroxyacetyl radical 8 March 2011 PAN formation Frank Flocke ACD FFL@ucar. edu CH 3 – C O – NO 2 hv, OH 64

Strongly temperature dependent equilibrium O CH 3 – C • + O 2 O CH 3 – C O + NO 2 O–O • PAN formation O – NO 2 hv, OH CH 3 C(O)H + OH or + hv (CH 3)2 C=O + hv 8 March 2011 CH 3 – C Frank Flocke ACD FFL@ucar. edu 65

Strongly temperature dependent equilibrium O CH 3 – C • + O 2 O CH 3 – C O + NO 2 O–O • CH 3 – C O – NO 2 hv, OH CH 3 C(O)H + OH or + hv (CH 3)2 C=O + hv Many VOC + OH 8 March 2011 PAN formation Frank Flocke ACD FFL@ucar. edu 66

Atmospheric Lifetime of PAN °F °C Thermal Photolysis OH 40 minutes 2 months 2 years 3 months 4 years 4 hrs. 1 day 1 week 1 month 1 year 8 March 2011 Frank Flocke ACD FFL@ucar. edu 67

a PAN’s life HNO 3, PANs NO 2 VOC NOx NO PANs O 3 CO, CH 4, long lived VOC NOx 8 March 2011 (cold) Frank Flocke ACD FFL@ucar. edu NOx O 3 (warm) 68

NOy partitioning polluted vs. remote 8 March 2011 Frank Flocke ACD FFL@ucar. edu Singh et al. , NASA 69

Arctic NOy 8 March 2011 Frank Flocke ACD FFL@ucar. edu 70

Atlanta: High anthropogenic and biogenic NMHC Power plants: Mainly biogenic NMHC from surrounding forest Johnsonville power plant: NOx emission controlled Cumberland power plant: very high NOx emission (no control) 8 March 2011 ATL, Cumb. , Johnsv. , PP, SOS 99 Frank Flocke ACD FFL@ucar. edu 71

New York City vs. Mexico City New York City Outflow NYC – low level outflow, lower VOC: Rapid conversion of NOx into HNO 3. Very little NOx remains one day downwind to produce additional ozone. MC –high VOC , and outflow at higher altitudes: Reactive nitrogen is carried out in its organic forms (PANs), which release NOx on a regional scale. This results in additional ozone production further downwind. Mexico City Outflow The high NOx and very high hydrocarbon emissions typical for a megacity like MC combine non-linearly to extend its impacts to a much larger region. 8 March 2011 Frank Flocke ACD FFL@ucar. edu 72

CO emissions (PANs ? ) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 73

Ratios of different PANs species as indicators of the relative importance of certain hydrocarbon species (and emitters) for the photochemical production of ozone biogenic or anthropogenic ? 8 March 2011 Frank Flocke ACD FFL@ucar. edu 74

O PPN CH 3 – CH 2 – C O – NO 2 Peroxypropionyl nitrate (Peroxypropionic nitric anhydride) CH 3 – CH 2 – CH 3 Propane 8 March 2011 PPN structure Frank Flocke ACD FFL@ucar. edu 75

Ethane + OH + NOx O 3 PAN PPN Pi. BN MPAN Propane + OH + NOx O 3 PAN PPN Pi. BN MPAN Alkanes>C 3 + OH + NOx O 3 PAN PPN Pi. BN MPAN What does PAN/PPN look like for anthropogenically polluted air? 8 March 2011 Formation of PANs from NMHC – Summary 1 Frank Flocke ACD FFL@ucar. edu 76

Tex. AQS 2000 campaign, urban and industrial pollution PAN vs. PPN Slope ~ 6 8 March 2011 PAN/PPN Houston all data Frank Flocke ACD FFL@ucar. edu 77

TRACE-P 2001 campaign - Asian urban and industr. pollution PAN vs. PPN Slope ~ 6 8 March 2011 PAN/PPN TRACE Frank Flocke ACD FFL@ucar. edu 78

O H 2 C MPAN C–C CH 3 O – NO 2 Peroxymethacryloyl nitrate (Methacryl-PAN) CH 2 C C – CH CH 3 Isoprene 8 March 2011 MPAN structure Frank Flocke ACD FFL@ucar. edu 79

Ethane + OH + NOx O 3 PAN PPN Pi. BN MPAN Alkanes>C 2 + OH + NOx O 3 PAN PPN Pi. BN MPAN Alkanes>C 3 + OH + NOx O 3 PAN PPN Pi. BN MPAN Isoprene + OH + NOx 8 March 2011 Formation of PANs from NMHC – Summary alk/iso 1 O 3 PAN Frank Flocke ACD FFL@ucar. edu PPN Pi. BN MPAN 80

SOS 99, all flights PAN – PPN correlation 8 March 2011 Frank Flocke ACD FFL@ucar. edu 81

PAN / PPN / MPAN multiple regression PAN/PPN ~ 6, PAN/MPAN ~ 3 8 March 2011 Frank Flocke ACD FFL@ucar. edu 82

What about Ozone / PAN ? 8 March 2011 Frank Flocke ACD FFL@ucar. edu 83

8 March 2011 Cumberland/Johnsonville PAN/O 3 Frank Flocke ACD FFL@ucar. edu 84

O 3 production from Isoprene in power plant plumes: • The yield of PAN from isoprene oxidation is about 20% (we know this from laboratory experiments) • The slope of ozone vs. PAN is about 15 molecules of ozone formed per molecule of PAN formed in the plumes (measured) • Most of the ozone is formed following oxidation of isoprene (we know this by the absence of PPN and presence of MPAN in these plumes) Ø The number of ozone molecules formed per isoprene molecule oxidized can be calculated to about 15 · 0. 2 = 3 • Important result to test plume models, photochemical point models (test of understanding of chemistry by comparison with isoprene flux estimates – isoprene is VERY short-lived!) 8 March 2011 Frank Flocke ACD FFL@ucar. edu 85

Problem - Homework The photolysis of acetone, (CH 3)2 CO and reaction of Acetaldehyde, CH 3 CHO with OH, are sources of PAN in the atmosphere. Consider only acetone photolysis CH 3 C(O)CH 3 + hv + O 2 CH 3 C(O)OO + NO CH 3 + CO 2 + NO 2 CH 3 C(O)OO + NO 2 PAN CH 3 C(O)OO + NO 2 Show that: • Steady-state [PAN] is independent of [NOx] • [PAN] increases with increasing O 3 and Acetone *use reaction constants from ACD Textbook 8 March 2011 Frank Flocke ACD FFL@ucar. edu 86

So does NOx just cycle between reservoir species and NO, NO 2 and hang around forever? 8 March 2011 Frank Flocke ACD FFL@ucar. edu 87

Tropospheric sinks of NOx 8 March 2011 NO 2 + OH + M HNO 3 + M HNO 3 + hv OH + NO 2 HNO 3 + OH H 2 O + NO 3 + NO 2 NO 3 + hv NO + O 2 (8%) HNO 3+H 2 O(liq) HNO 3 (liq) -2 Ox -HOx, -Ox NO 2 + O 3 NO 3 + O 2 NO 3 + NO 2 + M N 2 O 5 + M N 2 O 5 + H 2 O(liq) HNO 3(liq) -3 Ox Frank Flocke ACD FFL@ucar. edu 88

Tropospheric sinks of NOx • Formation of nitrate aerosol* • Uptake of HNO 3 onto dust • Deposition of (multifunctional) RONO 2, RC(O)OONO 2 onto plants and soils • Deposition of (multifunctional) RONO 2 onto aerosols * Reversible for NH 4 NO 3 8 March 2011 Frank Flocke ACD FFL@ucar. edu 89