Methyl halide emissions from savanna fires in southern Africa

Andreae, Meinrat O.; Atlas, E.; Harris, G. W.; Helas, G.; Kock, Annette; Koppmann, R.; Maenhaut, Willy; Manø, Stein; Pollock, W. H.; Rudolph, J.; Scharffe, D.; Schebeske, G; Welling, Michael

doi:10.1029/95jd01733

Cited by 167 publications

(132 citation statements)

References 27 publications

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“…[18][19][20][21][22] Having been so extensively studied, by both experimental [23][24][25][26][27] and computational [28][29][30][31][32][33][34][35][36] means, lends this class of reactions to be an outstanding starting position for benchmarking and refining new computational methods and techniques. In particular, the chloride/methyl chloride reaction is a strong candidate as a prototype reaction as it has been quite extensively studied in order to understand the exact nature of the transition state in the gas and condensed phases.…”

Section: Introductionmentioning

confidence: 99%

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Kuechler

York

2014

The Journal of Chemical Physics

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The nucleophilic attack of a chloride ion on methyl chloride is an important prototype S N 2 reaction in organic chemistry that is known to be sensitive to the effects of the surrounding solvent. Herein, we develop a highly accurate Specific Reaction Parameter (SRP) model based on the Austin Model 1 Hamiltonian for chlorine to study the effects of solvation into an aqueous environment on the reaction mechanism. To accomplish this task, we apply high-level quantum mechanical calculations to study the reaction in the gas phase and combined quantum mechanical/molecular mechanical simulations with TIP3P and TIP4P-ew water models and the resulting free energy profiles are compared with those determined from simulations using other fast semi-empirical quantum models. Both gas phase and solution results with the SRP model agree very well with experiment and provide insight into the specific role of solvent on the reaction coordinate. Overall, the newly parameterized SRP Hamiltonian is able to reproduce both the gas phase and solution phase barriers, suggesting it is an accurate and robust model for simulations in the aqueous phase at greatly reduced computational cost relative to comparably accurate ab initio and density functional models. © 2014 AIP Publishing LLC. [http://dx

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Section: Introductionmentioning

confidence: 99%

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Kuechler

York

2014

The Journal of Chemical Physics

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“…The major source of HCl in the atmosphere is biomass burning (Andreae et al, 1996), coal combustion and waste combustion , and also by the reaction of gaseous HNO 3 with NaCl in sea salt particles . Emission fluxes of 50 Tg Cl yr −1 , 6 Tg Cl yr −1 , 4.6 Tg Cl yr −1 , and 2 Tg Cl yr −1 for HCl are emitted globally to the atmosphere from dechlorination of sea salt aerosols (Graedel and Keene, 1995;Keene et al, 1999), biomass burning , coal combustion and waste burning , respectively.…”

Section: Introductionmentioning

confidence: 99%

Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)

et al. 2011

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Abstract. The atmospheric concentrations of gaseous HNO 3 , HCl and NH 3 and their relative salts have been measured during two field campaigns in the winter and in the summer of 2007 at Beijing (China), as part of CARE-BEIJING (Campaigns of Air Quality Research in Beijing and Surrounding Region). In this study, annular denuder technique used with integration times of 2 and 24h to collect inorganic and soluble PM 2.5 without interferences from gas-particle and particle-particle interactions. The results were discussed from the standpoint of temporal and diurnal variations and meteorological effects. Fine particulate Cl − , NH 4 were higher during summer (12.30 µg m −3 and 18.24 µg m −3 , respectively) than during winter (6.51 µg m −3 and 7.50 µg m −3 , respectively). Daily mean concentrations of fine particulate Cl − were higher during winter (2.94 µg m −3 ) than during summer (0.79 µg m −3 ), while fine particulate NO − 3 showed similar both in winter (8.38 µg m −3 ) and in summer (9.62 µg m −3 ) periods. The presence of large amounts of fine particulate NO − 3 even in summer are due to higher local and regional concentrations of NH 3 in the atmosphere available to neutralize H 2 SO 4 and HNO 3 , which is consistent with the observation that the measured particulate species were neutralized. The composition of fine particulate matter indicated the domination of (NH 4 ) 2 SO 4 during winter and summer periods. In addition, the high relative humidity conditions in summer periodCorrespondence to: A. Ianniello (ianniello@iia.cnr.it) seemed to dissolve a significant fraction of HNO 3 and NH 3 enhancing fine particulate NO − 3 and NH + 4 in the atmosphere. All measured particulate species showed diurnal similar patterns during the winter and summer periods with higher peaks in the early morning, especially in summer, when humid and stable atmospheric conditions occurred. These diurnal variations were affected by wind direction suggesting regional and local source influences. The fine particulate species were correlated with NO x and PM 2.5 , supporting the hypothesis that traffic may be also an important source of secondary particles.

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“…The global gridded meteorological data used for this research were prepared by the European Centre for MediumRange Weather Forecasting (ECMWF) [Bengtsson, 1985;Hollingsworth et al, 1986]. The various meteorological parameters were available twice daily (0000 and 1200 UTC) at a horizontal resolution of 2.5 ø longitude by 2.5 ø latitude at 13 isobaric levels (1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100, 70, and 50 hPa).…”

Section: Meteorological Datamentioning

confidence: 99%

Chemical characteristics of air from differing source regions during the Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A)

Board¹,

Fuelberg²,

Gregory³

et al. 1999

J. Geophys. Res.

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Abstract. Ten-day backward trajectories are used to determine the origins of air parcels arriving at airborne DC-8 chemical measurement sites during NASA's Pacific Exploratory Mission-Tropics A (PEM-T) that was conducted during August-October 1996. Those sites at which the air had a common geographical origin and transport history are grouped together, and statistical measures of chemical characteristics are computed. Temporal changes in potential temperature are used to determine whether trajectories experience a significant convective influence during the 10-day period. Those trajectories that do not experience a significant convective influence are divided into four geographical categories depending on their origins and paths. Air parcels originating over Africa and South America are characterized by enhanced mixing ratios of 03, CO, HNO3, and PAN. The backward trajectories travel at high altitudes (--•10-11 km), covering long distances due to strong upper-tropospheric westerly winds. The observed enhancement of combustionrelated species is attributed to biomass burning from distant sources to the west, extending even to South America. The relatively large value of Be-7 probably is due either to less efficient removal of aerosols from upper tropospheric air or to small stratospheric contributions. Aged marine parcels are found to have relatively small concentrations of burning-related species. Although these trajectories arrive at a wide range of aircraft altitudes, they do not pass over a land mass during the preceding 10-day period. Air passing over Australia but no other land mass exhibits a combustion signature; however, photochemical product species such as 03 and PAN are less enhanced than in the longrange transport category. These trajectories travel shorter distances and are at lower altitudes (--•5-8 km) than those reaching Africa and/or South America. The combustion influence on these parcels is attributed to biomass burning emissions injected over Australia. That burning is less widespread than in Africa and South America. Finally, trajectories originating over Southeast Asia appear to receive a weak combustion influence. However, compared to Africa and South America, Southeast Asia has a relatively small incidence of biomass burning. There is little combustion input from Australia due to the high transport altitudes compared to the lower heights of the convection. The Southeast Asian parcels exhibit the greatest NO x to •NO/ratio of any category, perhaps due to lightning. Parcels experiencing a significant convective influence also are examined. Most of these parcels pass through widespread, persistent convection along either the South Pacific Convergence Zone or Intertropical Convergence Zone approximately 5 days prior to arriving at the aircraft locations. Thus the category mostly represents marine convection. Mixing ratios of peroxides and acids in the convective category are found to be smaller than in parcels not experiencing convection. Small mixing ratios of Be-7 and Pb-210 suggest particle...

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Methyl halide emissions from savanna fires in southern Africa

Cited by 167 publications

References 27 publications

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)

Chemical characteristics of air from differing source regions during the Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A)

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Methyl halide emissions from savanna fires in southern Africa

Cited by 167 publications

References 27 publications

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl− attack on CH3Cl

Chemical characteristics of inorganic ammonium salts in PM&lt;sub&gt;2.5&lt;/sub&gt; in the atmosphere of Beijing (China)

Chemical characteristics of air from differing source regions during the Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A)

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Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)