26
|
Khan MAH, Percival CJ, Caravan RL, Taatjes CA, Shallcross DE. Criegee intermediates and their impacts on the troposphere. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2018; 20:437-453. [PMID: 29480909 DOI: 10.1039/c7em00585g] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Criegee intermediates (CIs), carbonyl oxides formed in ozonolysis of alkenes, play key roles in the troposphere. The decomposition of CIs can be a significant source of OH to the tropospheric oxidation cycle especially during nighttime and winter months. A variety of model-measurement studies have estimated surface-level stabilized Criegee intermediate (sCI) concentrations on the order of 1 × 104 cm-3 to 1 × 105 cm-3, which makes a non-negligible contribution to the oxidising capacity in the terrestrial boundary layer. The reactions of sCI with the water monomer and the water dimer have been found to be the most important bimolecular reactions to the tropospheric sCI loss rate, at least for the smallest carbonyl oxides; the products from these reactions (e.g. hydroxymethyl hydroperoxide, HMHP) are also of importance to the atmospheric oxidation cycle. The sCI can oxidise SO2 to form SO3, which can go on to form a significant amount of H2SO4 which is a key atmospheric nucleation species and therefore vital to the formation of clouds. The sCI can also react with carboxylic acids, carbonyl compounds, alcohols, peroxy radicals and hydroperoxides, and the products of these reactions are likely to be highly oxygenated species, with low vapour pressures, that can lead to nucleation and SOA formation over terrestrial regions.
Collapse
|
27
|
Sheps L, Rotavera B, Eskola AJ, Osborn DL, Taatjes CA, Au K, Shallcross DE, Khan MAH, Percival CJ. The reaction of Criegee intermediate CH 2OO with water dimer: primary products and atmospheric impact. Phys Chem Chem Phys 2018; 19:21970-21979. [PMID: 28805226 DOI: 10.1039/c7cp03265j] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The rapid reaction of the smallest Criegee intermediate, CH2OO, with water dimers is the dominant removal mechanism for CH2OO in the Earth's atmosphere, but its products are not well understood. This reaction was recently suggested as a significant source of the most abundant tropospheric organic acid, formic acid (HCOOH), which is consistently underpredicted by atmospheric models. However, using time-resolved measurements of reaction kinetics by UV absorption and product analysis by photoionization mass spectrometry, we show that the primary products of this reaction are formaldehyde and hydroxymethyl hydroperoxide (HMHP), with direct HCOOH yields of less than 10%. Incorporating our results into a global chemistry-transport model further reduces HCOOH levels by 10-90%, relative to previous modeling assumptions, which indicates that the reaction CH2OO + water dimer by itself cannot resolve the discrepancy between the measured and predicted HCOOH levels.
Collapse
|
28
|
Winiberg FAF, Percival CJ, Shannon R, Khan MAH, Shallcross DE, Liu Y, Sander SP. Reaction kinetics of OH + HNO3 under conditions relevant to the upper troposphere/lower stratosphere. Phys Chem Chem Phys 2018; 20:24652-24664. [DOI: 10.1039/c8cp04193h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Key upper atmosphere reaction of HNO3 + OH studied over extended pressure and temperature range using new alternative detection method.
Collapse
|
29
|
H. Khan MA, Morris WC, Galloway M, A. Shallcross B, Percival CJ, Shallcross DE. An Estimation of the Levels of Stabilized Criegee Intermediates in the UK Urban and Rural Atmosphere Using the Steady-State Approximation and the Potential Effects of These Intermediates on Tropospheric Oxidation Cycles. INT J CHEM KINET 2017; 49:611-621. [PMID: 28781420 PMCID: PMC5519938 DOI: 10.1002/kin.21101] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 05/05/2017] [Accepted: 05/05/2017] [Indexed: 01/18/2023]
Abstract
Levels of the stabilized Criegee Intermediate (sCI), produced via the ozonolysis of unsaturated volatile organic compounds (VOCs), were estimated at two London urban sites (Marylebone Road and Eltham) and one rural site (Harwell) in the UK over the period of 1998-2012. The steady-state approximation was applied to data obtained from the NETCEN (National Environmental Technology Centre) database, and the levels of annual average sCI were estimated to be in the range of 30-3000 molecules cm-3 for UK sites. A consistent diurnal cycle of sCI concentration is estimated for the UK sites with increasing levels during daylight hours, peaking just after midday. The seasonal pattern of sCI shows higher levels in spring with peaks around May due to the higher levels of O3. The ozone weekend effect resulted in higher sCI in UK urban areas during weekend. The sCI data were modeled using the information provided by the Air Quality Improvement Research Program (AQIRP) and found that the modeled production was five- to six-fold higher than our estimated data, and therefore the estimated sCI concentrations in this study are thought to be lower estimates only. Compared with nighttime, 1.3- to 1.8-fold higher sCI exists under daytime conditions. Using the levels of sCI estimated at Marylebone Road, globally the oxidation rates of NO2 + sCI (22.4 Gg/yr) and SO2 + sCI (37.6 Gg/yr) in urban areas can increase their effect in the troposphere and potentially further alter the oxidizing capacity of the troposphere. Further investigations of modeled sCI show that CH3CHOO (64%) and CH2OO (13%) are dominant among all contributing sCI at the UK sites.
Collapse
|
30
|
Chhantyal-Pun R, McGillen MR, Beames JM, Khan MAH, Percival CJ, Shallcross DE, Orr-Ewing AJ. Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201703700] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
31
|
Chhantyal-Pun R, McGillen MR, Beames JM, Khan MAH, Percival CJ, Shallcross DE, Orr-Ewing AJ. Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates. Angew Chem Int Ed Engl 2017; 56:9044-9047. [PMID: 28614628 PMCID: PMC5575497 DOI: 10.1002/anie.201703700] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 06/07/2017] [Indexed: 11/11/2022]
Abstract
The rate coefficients for gas-phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240-340 K. The rate coefficients k(CH2 OO + CF3 COOH)=(3.4±0.3)×10-10 cm3 s-1 and k((CH3 )2 COO + CF3 COOH)=(6.1±0.2)×10-10 cm3 s-1 at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm3 s-1 ]=(3.8±2.6)×10-18 T2 exp((1620±180)/T) + 2.5×10-10 and k [cm3 s-1 ]=(4.9±4.1)×10-18 T2 exp((1620±230)/T) + 5.2×10-10 for the CH2 OO + CF3 COOH and (CH3 )2 COO + CF3 COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.
Collapse
|
32
|
Caravan RL, Khan MAH, Rotavera B, Papajak E, Antonov IO, Chen MW, Au K, Chao W, Osborn DL, Lin JJM, Percival CJ, Shallcross DE, Taatjes CA. Products of Criegee intermediate reactions with NO2: experimental measurements and tropospheric implications. Faraday Discuss 2017; 200:313-330. [DOI: 10.1039/c7fd00007c] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The reactions of Criegee intermediates with NO2 have been proposed as a potentially significant source of the important nighttime oxidant NO3, particularly in urban environments where concentrations of ozone, alkenes and NOx are high. However, previous efforts to characterize the yield of NO3 from these reactions have been inconclusive, with many studies failing to detect NO3. In the present work, the reactions of formaldehyde oxide (CH2OO) and acetaldehyde oxide (CH3CHOO) with NO2 are revisited to further explore the product formation over a pressure range of 4–40 Torr. NO3 is not observed; however, temporally resolved and [NO2]-dependent signal is observed at the mass of the Criegee–NO2 adduct for both formaldehyde- and acetaldehyde-oxide systems, and the structure of this adduct is explored through ab initio calculations. The atmospheric implications of the title reaction are investigated through global modelling.
Collapse
|
33
|
Chhantyal-Pun R, Welz O, Savee JD, Eskola AJ, Lee EPF, Blacker L, Hill HR, Ashcroft M, Khan MAH, Lloyd-Jones GC, Evans L, Rotavera B, Huang H, Osborn DL, Mok DKW, Dyke JM, Shallcross DE, Percival CJ, Orr-Ewing AJ, Taatjes CA. Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH3)2COO. J Phys Chem A 2016; 121:4-15. [DOI: 10.1021/acs.jpca.6b07810] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
34
|
Shallcross DE, Leather KE, Bacak A, Xiao P, Lee EPF, Ng M, Mok DKW, Dyke JM, Hossaini R, Chipperfield MP, Khan MAH, Percival CJ. Reaction between CH3O2 and BrO Radicals: A New Source of Upper Troposphere Lower Stratosphere Hydroxyl Radicals. J Phys Chem A 2015; 119:4618-32. [DOI: 10.1021/jp5108203] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
35
|
Chhantyal-Pun R, Davey A, Shallcross DE, Percival CJ, Orr-Ewing AJ. A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy. Phys Chem Chem Phys 2015; 17:3617-26. [DOI: 10.1039/c4cp04198d] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A rate coefficient is reported for the CH2OO self-reaction and evidence presented for SO2-catalysed CH2OO isomerization or intersystem crossing.
Collapse
|
36
|
Shallcross DE, Taatjes CA, Percival CJ. Criegee intermediates in the indoor environment: new insights. INDOOR AIR 2014; 24:495-502. [PMID: 24512513 DOI: 10.1111/ina.12102] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Accepted: 02/02/2014] [Indexed: 06/03/2023]
Abstract
Criegee intermediates are formed in the ozonolysis of alkenes and play an important role in indoor chemistry, notably as a source of OH radicals. Recent studies have shown that these Criegee intermediates react very quickly with NO2 , SO2 , and carbonyls, and in this study, steady-state calculations are used to inspect the potential impact of these data on indoor chemistry. It is shown that these reactions could accelerate NO3 formation and SO2 removal in the indoor environment significantly. In addition, reaction between Criegee intermediates and halogenated carbonyls could provide a significant loss process indoors, where currently one does not exist.
Collapse
|
37
|
|
38
|
Higgins CM, Evans LA, Lloyd-Jones GC, Shallcross DE, Tew DP, Orr-Ewing AJ. Quantum Yields for Photochemical Production of NO2 from Organic Nitrates at Tropospherically Relevant Wavelengths. J Phys Chem A 2014; 118:2756-64. [DOI: 10.1021/jp501517t] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
39
|
Welz O, Eskola AJ, Sheps L, Rotavera B, Savee JD, Scheer AM, Osborn DL, Lowe D, Murray Booth A, Xiao P, Anwar H Khan M, Percival CJ, Shallcross DE, Taatjes CA. Rate coefficients of C(1) and C(2) Criegee intermediate reactions with formic and acetic Acid near the collision limit: direct kinetics measurements and atmospheric implications. Angew Chem Int Ed Engl 2014; 53:4547-50. [PMID: 24668781 PMCID: PMC4499262 DOI: 10.1002/anie.201400964] [Citation(s) in RCA: 147] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Indexed: 11/17/2022]
Abstract
Rate coefficients are directly determined for the reactions of the Criegee intermediates (CI) CH2OO and CH3CHOO with the two simplest carboxylic acids, formic acid (HCOOH) and acetic acid (CH3COOH), employing two complementary techniques: multiplexed photoionization mass spectrometry and cavity-enhanced broadband ultraviolet absorption spectroscopy. The measured rate coefficients are in excess of 1×10−10 cm3 s−1, several orders of magnitude larger than those suggested from many previous alkene ozonolysis experiments and assumed in atmospheric modeling studies. These results suggest that the reaction with carboxylic acids is a substantially more important loss process for CIs than is presently assumed. Implementing these rate coefficients in global atmospheric models shows that reactions between CI and organic acids make a substantial contribution to removal of these acids in terrestrial equatorial areas and in other regions where high CI concentrations occur such as high northern latitudes, and implies that sources of acids in these areas are larger than previously recognized.
Collapse
|
40
|
Welz O, Eskola AJ, Sheps L, Rotavera B, Savee JD, Scheer AM, Osborn DL, Lowe D, Murray Booth A, Xiao P, Anwar H. Khan M, Percival CJ, Shallcross DE, Taatjes CA. Rate Coefficients of C1 and C2 Criegee Intermediate Reactions with Formic and Acetic Acid Near the Collision Limit: Direct Kinetics Measurements and Atmospheric Implications. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201400964] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
41
|
Copeland G, Lee EPF, Williams RG, Archibald AT, Shallcross DE, Dyke JM. Determination of the photolysis rate coefficient of monochlorodimethyl sulfide (MClDMS) in the atmosphere and its implications for the enhancement of SO2 production from the DMS + Cl2 reaction. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:1557-1565. [PMID: 24280000 DOI: 10.1021/es402956r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In this work, the photolysis rate coefficient of CH3SCH2Cl (MClDMS) in the lower atmosphere has been determined and has been used in a marine boundary layer (MBL) box model to determine the enhancement of SO2 production arising from the reaction DMS + Cl2. Absorption cross sections measured in the 28000-34000 cm(-1) region have been used to determine photolysis rate coefficients of MClDMS in the troposphere at 10 solar zenith angles (SZAs). These have been used to determine the lifetimes of MClDMS in the troposphere. At 0° SZA, a photolysis lifetime of 3-4 h has been obtained. The results show that the photolysis lifetime of MClDMS is significantly smaller than the lifetimes with respect to reaction with OH (≈ 4.6 days) and with Cl atoms (≈ 1.2 days). It has also been shown, using experimentally derived dissociation energies with supporting quantum-chemical calculations, that the dominant photodissocation route of MClDMS is dissociation of the C-S bond to give CH3S and CH2Cl. MBL box modeling calculations show that buildup of MClDMS at night from the Cl2 + DMS reaction leads to enhanced SO2 production during the day. The extra SO2 arises from photolysis of MClDMS to give CH3S and CH2Cl, followed by subsequent oxidation of CH3S.
Collapse
|
42
|
Taatjes CA, Shallcross DE, Percival CJ. Research frontiers in the chemistry of Criegee intermediates and tropospheric ozonolysis. Phys Chem Chem Phys 2014; 16:1704-18. [DOI: 10.1039/c3cp52842a] [Citation(s) in RCA: 214] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
43
|
Percival CJ, Welz O, Eskola AJ, Savee JD, Osborn DL, Topping DO, Lowe D, Utembe SR, Bacak A, McFiggans G, Cooke MC, Xiao P, Archibald† AT, Jenkin ME, Derwent RG, Riipinen I, Mok DWK, Lee EPF, Dyke JM, Taatjes CA, Shallcross DE. Regional and global impacts of Criegee intermediates on atmospheric sulphuric acid concentrations and first steps of aerosol formation. Faraday Discuss 2013; 165:45-73. [DOI: 10.1039/c3fd00048f] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
44
|
Lee EPF, Mok DKW, Shallcross DE, Percival CJ, Osborn DL, Taatjes CA, Dyke JM. Spectroscopy of the Simplest Criegee Intermediate CH2OO: Simulation of the First Bands in Its Electronic and Photoelectron Spectra. Chemistry 2012; 18:12411-23. [DOI: 10.1002/chem.201200848] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Indexed: 11/11/2022]
|
45
|
Ghalaieny M, Bacak A, McGillen M, Martin D, Knights AV, O'Doherty S, Shallcross DE, Percival CJ. Determination of gas-phase ozonolysis rate coefficients of a number of sesquiterpenes at elevated temperatures using the relative rate method. Phys Chem Chem Phys 2012; 14:6596-602. [PMID: 22456861 DOI: 10.1039/c2cp23988d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The rates of ozonolysis of four sesquiterpenes, β-caryophyllene, α-humulene, isolongifolene and α-cedrene, are determined in the gas phase at an elevated temperature of 366 ± 3 K and a pressure of ~780 Torr using the EXTreme RAnge chamber (EXTRA). The experimentally obtained rate coefficients agree with extrapolated room temperature rate coefficients for isolongifolene and α-cedrene but not for β-caryophyllene and α-humulene, which were found to be three orders of magnitude slower than this in the literature. These new measurements support the hypothesis that operating under ambient conditions, kinetic measurements of condensable species can be influenced adversely by heterogeneous processes and should therefore be treated with caution.
Collapse
|
46
|
Henne S, Shallcross DE, Reimann S, Xiao P, Brunner D, O'Doherty S, Buchmann B. Future emissions and atmospheric fate of HFC-1234yf from mobile air conditioners in Europe. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:1650-8. [PMID: 22225403 DOI: 10.1021/es2034608] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
HFC-1234yf (2,3,3,3-tetrafluoropropene) is under discussion for replacing HFC-134a (1,1,1,2-tetrafluoroethane) as a cooling agent in mobile air conditioners (MACs) in the European vehicle fleet. Some HFC-1234yf will be released into the atmosphere, where it is almost completely transformed to the persistent trifluoroacetic acid (TFA). Future emissions of HFC-1234yf after a complete conversion of the European vehicle fleet were assessed. Taking current day leakage rates and predicted vehicle numbers for the year 2020 into account, European total HFC-1234yf emissions from MACs were predicted to range between 11.0 and 19.2 Gg yr(-1). Resulting TFA deposition rates and rainwater concentrations over Europe were assessed with two Lagrangian chemistry transport models. Mean European summer-time TFA mixing ratios of about 0.15 ppt (high emission scenario) will surpass previously measured levels in background air in Germany and Switzerland by more than a factor of 10. Mean deposition rates (wet + dry) of TFA were estimated to be 0.65-0.76 kg km(-2) yr(-1), with a maxium of ∼2.0 kg km(-2) yr(-1) occurring in Northern Italy. About 30-40% of the European HFC-1234yf emissions were deposited as TFA within Europe, while the remaining fraction was exported toward the Atlantic Ocean, Central Asia, Northern, and Tropical Africa. Largest annual mean TFA concentrations in rainwater were simulated over the Mediterranean and Northern Africa, reaching up to 2500 ng L(-1), while maxima over the continent of about 2000 ng L(-1) occurred in the Czech Republic and Southern Germany. These highest annual mean concentrations are at least 60 times lower than previously determined to be a safe level for the most sensitive aquatic life-forms. Rainwater concentrations during individual rain events would still be 1 order of magnitude lower than the no effect level. To verify these results future occasional sampling of TFA in the atmospheric environment should be considered. If future HFC-1234yf emissions surpass amounts used here studies of TFA accumulation in endorheic basins and other sensitive areas should be aspired.
Collapse
|
47
|
Leather KE, Bacak A, Wamsley R, Archibald AT, Husk A, Shallcross DE, Percival CJ. Temperature and pressure dependence of the rate coefficient for the reaction between ClO and CH3O2 in the gas-phase. Phys Chem Chem Phys 2012; 14:3425-34. [DOI: 10.1039/c2cp22834c] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
|
48
|
Taatjes CA, Welz O, Eskola AJ, Savee JD, Osborn DL, Lee EPF, Dyke JM, Mok DWK, Shallcross DE, Percival CJ. Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone. Phys Chem Chem Phys 2012; 14:10391-400. [DOI: 10.1039/c2cp40294g] [Citation(s) in RCA: 123] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
49
|
Harrison TG, Shallcross DE, Norman NC, Sewry JD, Davies-Coleman MT. Publicising chemistry in a multicultural society through chemistry outreach. S AFR J SCI 2011. [DOI: 10.4102/sajs.v107i11/12.669] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
|
50
|
Khan MAH, Hoque MMN, Alam SS, Ashfold MJ, Nickless G, Shallcross DE. Estimation and comparison of night-time OH levels in the UK urban atmosphere using two different analysis methods. J Environ Sci (China) 2011; 23:60-64. [PMID: 21476341 DOI: 10.1016/s1001-0742(10)60373-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Night-time OH levels have been determined for UK urban surface environments using two methods, the decay and steady state approximation methods. Measurement data from the UK National Environmental Technology Centre archive for four urban sites (Bristol, Harwell, London Eltham and Edinburgh) over the time period of 1996 to 2000 have been used in this study. Three reactive alkenes, namely isoprene, 1,3-butadiene and trans-2-pentene were chosen for the calculation of OH levels by the decay method. Hourly measurements of NO, NO2, O3, CO and 20 VOCs were used to determine night-time OH level using the steady state approximation method. Our results showed that the night-time OH levels were in the range of 1 x 10(5) - 1 x 10(6) molecules/cm3 at these four urban sites in the UK. The application of a t-test of these analyses indicated that except Bristol, there was no significant difference between the OH levels found from the decay and steady state approximation methods. Night-time levels of the OH radical appeared to peak in summer and spring time tracking the night-time O3 levels which also passed through a maximum at this time.
Collapse
|