Showing papers by "Paul J. Crutzen published in 1999"

Iodine chemistry and its role in halogen activation and ozone loss in the marine boundary layer: A model study

Abstract: A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O → 2OH, HO2 + O3 → OH + 2O2, and OH + O3 → HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.

Biomass burning as a source of formaldehyde, acetaldehyde, methanol, acetone, acetonitrile and hydrogen cyanide

Abstract: Using a novel experimental technique, based on proton transfer reaction mass spectrometry, from measurements of emissions from laboratory scale biomass burning experiments, we have estimated the source strengths of several potential HOx producing gases: formaldehyde, acetaldehyde, methanol and acetone. The derived global average emissions are 5–13; 3.8–10; 1.5-4; 2.3-6.1 Tg y−1, respectively. The resulting global average HOx production from photochemical decay of these gases is 3 × 109 molecules cm−2 s−1. Although relatively small in a global context, these emissions are significant for the photochemistry in fresh fire plumes. From our measurements are also estimated global source strengths from biomass burning for CH3CN and HCN of 0.4-1.0; 0.2-0.6 Tg y−1 respectively. The biomass burning emissions of CH3CN may well dominate the global source of this compound, which thus might well be a unique tracer for biomass burning. Some discrepancies between experimental studies must, however, be resolved.

Acetone, methanol, and other partially oxidized volatile organic emissions from dead plant matter by abiological processes: Significance for atmospheric HOx chemistry

Abstract: In this paper, attention is called to the significance of abiological production of partially oxidized volatile organic carbons (POVOCs) from the decay of dead plant material. Measured relative emission of acetone and methanol can be at least 10−4 and 3 - 5 × 10−4 g g−1of decaying dry plant matter, respectively. If these results may be extrapolated, global annual emissions of 6–8 Tg of acetone and 18 – 40 Tg of methanol would result, adding strongly to the estimated total emissions of these compounds to the atmosphere. Because acetone and methanol, through OH and HO2 formation, play significant roles in the chemistry of the atmosphere, further research is strongly needed to quantify the emissions of acetone, methanol, and other POVOCs

Arctic Ozone Loss Due to Denitrification

Abstract: Measurements from the winter of 1994-95 indicating removal of total reactive nitrogen from the Arctic stratosphere by particle sedimentation were used to constrain a microphysical model. The model suggests that denitrification is caused predominantly by nitric acid trihydrate particles in small number densities. The denitrification is shown to increase Arctic ozone loss substantially. Sensitivity studies indicate that the Arctic stratosphere is currently at a threshold of denitrification. This implies that future stratospheric cooling, induced by an increase in the anthropogenic carbon dioxide burden, is likely to enhance denitrification and to delay until late in the next century the return of Arctic stratospheric ozone to preindustrial values.

On the background photochemistry of tropospheric ozone

Abstract: We present a largely tutorial overview of the main processes that influence the photochemistry of the background troposphere. This is mostly driven by the photolysis of ozone by solar ultraviolet radiation of wavelengths shorter than about 340 nm, resulting in production of excited O( 1 D) atoms, whose reaction with water vapor produces OH radicals. In the background atmosphere the OH radicals mostly react with CO, and with CH 4 and some of its oxidation products, which in turn are oxidized by OH. Depending on the availability of NO x , catalysts, ozone may be produced or destroyed in amounts that are much greater than the downward flux of ozone from the stratosphere to the troposphere. Using the 3D chemical-transport model MATCH, global distributions and budget analyses are presented for tropospheric O 3 , CH 4 , CO, and the “odd hydrogen” compounds OH, HO 2 and H 2 O 2 . We show that OH is present in maximum concentrations in the tropics, and that most of the chemical breakdown of CO and CH 4 also occurs in equatorial regions. We also split the troposphere into continental and marine regions, and show that there is a tremendous difference in photochemical O 3 and OH production for these regions, much larger than the difference between the northern hemisphere and southern hemisphere. Finally, we show the results from a numerical simulation in which we reduced the amount of ozone in the model stratosphere by a factor of 10 (which in turn reduced the flux of O 3 into the troposphere by about the same factor). Nevertheless, for summer conditions, model calculated O 3 mixing ratios below 5 km in the mid to high latitudes were about 70–90% as high as those calculated with the full downward flux of ozone from the stratosphere. This indicates that, at least under these conditions, O 3 concentrations in the lower troposphere are largely controlled by in situ photochemistry, with only a secondary influence from stratospheric influx. DOI: 10.1034/j.1600-0889.1999.00010.x

Influence of NOx emissions from ships on tropospheric photochemistry and climate

Abstract: Emissions of nitrogen oxides (NOx, the sum of NO and NO2) from fossil-fuel burning dominate the NOx burden of the lower troposphere in many regions1. These emissions increase tropospheric ozone and hydroxyl-radical concentrations over their natural ‘background’ levels, thereby increasing the oxidizing power of the atmosphere2. Fossil-fuel emissions of NOx (refs 3, 4) account for about half of the global NOx source to the atmosphere; other significant sources are from biomass burning5, soil emissions6, aircraft exhausts7 and lightning8, all primarily continental. However, ocean-going ships burning fossil fuels may also contribute a significant fraction (>10%) to global NOx production9. Here we use NOx emission data and a high-resolution chemistry–transport model to estimate that ship NOx emissions result in a more than 100-fold increase in surface NOx concentrations in heavily traversed ocean regions. This enhancement has a notable effect on modelled surface ozone and hydroxyl-radical concentrations. In particular, a predicted fivefold increase in the July hydroxyl-radical burden over the northern Atlantic and Pacific oceans would be expected to reduce the atmospheric lifetimes of reactive greenhouse gases—such as methane—as well as to increase aerosol production rates and cloud reflectivities, therefore exerting a cooling influence on the climate.

A model for studies of tropospheric photochemistry: Description, global distributions, and evaluation

Abstract: A model of atmospheric photochemistry and transport has been developed and applied toward investigating global tropospheric chemistry. The Model of Atmospheric Transport and Chemistry - Max-Planck-Institute for Chemistry version (MATCH-MPIC) is described and key characteristics of its global simulation are presented and compared to available observations. MATCH-MPIC is an “offline” model which reads in gridded time-dependent values for the most basic meteorological parameters (e.g., temperature, surface pressure, horizontal winds), then uses these to compute further meteorological parameters required for atmospheric chemistry simulations (convective transport, cloud microphysics, etc.). The meteorology component of MATCH-MPIC simulates transport by advection, convection, and dry turbulent mixing, as well as the full tropospheric hydrological cycle (water vapor transport, condensation, evaporation, and precipitation). The photochemistry component of MATCH-MPIC represents the major known sources (e.g., industry, biomass burning), transformations (chemical reactions and photolysis), and sinks (e.g., wet and dry deposition) which affect the O3hyphen;HOx-NOy-CH4-CO photochemical framework of the “background” troposphere. The results of two versions of the model are considered, focusing on the more recent version. O3 is in relatively good agreement with observed soundings, although it is generally underestimated at low levels and overestimated at high levels, particularly for the more recent version of the model. We conclude that the simulated stratosphere-troposphere flux of O3 is too large, despite the fact that the total flux is 1100 Tg(O3)/yr, whereas the upper limit estimated in recent literature is over 1400 Tg(O3)/yr. The OH distribution yields a tropospheric CH4 lifetime of 10.1 years, in contrast to the lifetime of 7.8 years in the earlier model version, which nearly spans the range of current estimates in the literature (7.5–10.2 years). Surface CO mixing ratios are in good agreement with observations. NO is generally underestimated, a problem similar to what has also been found in several other recent model studies. HNO3 is also considerably underestimated. H2O2 and CH3OOH, on the other hand, are in relatively good agreement with available observations, though both tend to be underestimated at high concentrations and overestimated at low concentrations. Possible reasons for these differences are considered.

Ozone in the remote marine boundary layer: A possible role for halogens

Abstract: On the spring 1995 cruise of the National Oceanic and Atmospheric Administration research vessel Malcolm Baldrige, we measured very large diurnal variations in ozone concentrations in the marine boundary layer. Average diurnal variations of about 32% of the mean were observed over the tropical Indian Ocean. We simulated these observations with the Model of Chemistry in Clouds and Aerosols, a photochemical box model with detailed aerosol chemistry. The model was constrained with photolysis rates, humidity, aerosol concentrations, NO, CO, and O 3 specified by shipboard observations and ozonesondes. Conventional homogeneous chemistry, where ozone photolysis to O( 1 D) and HO x chemistry dominate ozone destruction, can account for a diurnal variation of only about 12%. On wet sea-salt aerosols (at humidities above the deliquescence point), absorption of HOBr leads to release of BrCl and Br 2 , which photolyze to produce Br atoms that may provide an additional photochemical ozone sink. After 8 days of simulation, these Br atoms reach a peak concentration of 1.2 x 10 7 cm -3 at noon and destroy ozone through a catalytic cycle involving BrO and HOBr. Reactive Br lost to HBr can be absorbed into the aerosol phase and reactivated. The model predicts a diurnal variation in O 3 of 22% with aerosol-derived Br reaction explaining much, but not all, of the observed photochemical loss. The lifetime of ozone under these conditions is short, about 2 days. These results indicate that halogens play an important role in oxidation processes and the ozone budget in parts of the remote marine boundary layer.

CARIBIC—Civil Aircraft for Global Measurement of Trace Gases and Aerosols in the Tropopause Region

Abstract: The deployment of measurement equipment in passenger aircraft for the observation of atmospheric trace constituents is described. The package of automated instruments that is installed in a one-ton-capacity aircraft freight container positioned in the forward cargo bay of a Boeing 767 ER can register a vast amount of atmospheric data during regular long-distance flights. The air inlet system that is mounted on the fuselage directly below the container comprises an aerosol inlet, a separate inlet for trace-gas sampling, and an air exhaust. All instruments, the central computer, and power supply are mounted in aviation-approved racks that slide into the reinforced container. The current instrument package comprises a fast-response chemiluminescence sensor and a conventional UV absorption detector for O3; a gas chromatograph for CO; two condensation nuclei counters for particles larger than 5 and 12 nm; and a 12-canister large-capacity whole air sampler for laboratory trace-gas analysis and isotopic...

The role of BrNO3 in marine tropospheric chemistry: A model study

Abstract: Laboratory studies have shown that bromine nitrate (BrNO3) reacts on sulfuric acid and on ice particles Here we investigate the potential role of BrNO3 in the marine boundary layer (mbl) assuming that it reacts on sea-salt particles as well Using the chemical box model MOCCA we find that heterogeneous reactions of BrNO3 on aerosol particles could affect the chemistry in four major ways: 1) They increase loss of NOx (=NO+NO2) from the gas phase; 2) They accelerate loss of bromide and chloride from sea-salt aerosols This dehalogenation occurs without the consumption of aerosol acidity; 3) The resulting loss of NOx and the increase of gas-phase bromine species both lead to O3 destruction; 4) The resulting increase of reactive chlorine species affects gas-phase hydrocarbons as well as S(IV) oxidation by HOCl in sea-salt aerosols

CO emissions from degrading plant matter.

Abstract: CO emissions from degrading deciduous leaf and grass matter have been investigated in laboratory and field measurements. CO emissions are induced both photochemically and thermally. Photochemical CO production can be described by a 2nd-order polynomial in light intensity and exhibits a hysteresis effect, not previously reported. Humid material showed higher CO emissions than dry material. A preliminary, relative action spectrum for the photochemically induced CO emissions is presented. Although UV irradiation caused most of the CO production, visible light also caused up to 40% of the emissions. We propose a cleavage of the cellulose chain as the important step prior to CO production. Thermal CO emissions from degrading plant material obey an Arrhenius type equation (presented for several species in this paper), but emissions are lower than those induced photochemically. During our field measurements on dry grasses in a South African savanna we found a strong influence of incident radiation intensity and temperature on measured CO fluxes. Solely photochemical CO production from the grasses is calculated by subtraction of soil fluxes and thermally induced grass CO emissions from the total CO emissions. CO emissions and hysteresis differ between the grasses investigated and may be interpreted by the grass' colour and their architecture. Deposition of CO on the soils was much lower than CO emission from the dry grasses during daytime. Nighttime data show that possible thermal CO production from the grasses may partially compensate for CO deposition on the soils for several hours after sunset depending on temperature. DOI: 10.1034/j.1600-0889.1999.t01-4-00003.x

Kinetics and Products of the Reactions BrO + DMS and Br + DMS at 298 K

Abstract: The kinetics of the reaction BrO + DMS → products (1), were examined by use of pulsed-laser photolytic generation and time-resolved detection of the BrO radical by absorption spectroscopy at total ...

CO emissions from degrading plant matter. Part II: Estimate of a global source strength

Abstract: From relationships between integrated daily CO emissions and received solar radiation obtained for different standing dead grasses in field experiments in a savanna region in South Africa, and making use of ecosystem and solar irradiation databases, we derive estimates on global CO production and seasonality from photochemical decay of dry grasses and litter. The photochemical CO source strength from standing dead plant material and litter in various grassland ecosystems and deciduous forests ranges from 20 to 65 Tg CO per year (1 Tg = 10 12 g). Accounting for potentially CO emitting ecosystems not included in the data set, we estimate that 60 ± 30 Tg of CO are annually emitted by photochemical degradation of decaying plant matter, mostly in the tropics. We further estimate thermal CO production from the global topsoil non-woody litter pool on the basis of global climate data and measured Arrhenius parameters to add another 40 Tg CO per year, much depending on the chosen parameters, and probably uncertain by a factor of 2. The total global source of CO by these mechanisms may thus be in the range 100 +70 −50 Tg CO per year. Although the estimated CO source strength is a relatively small contribution to the global CO budget (2–8%), CO emissions may significantly compensate for CO deposition on soils in the tropics during certain times of the year. Currently, modelling studies mostly impose a constant CO deposition velocity from the atmosphere to the soil surface, based generally on measurements on bare soil. Future modelling efforts may need to include geographical and photochemical factors which play a role in CO exchange in tropical ecosystems. DOI: 10.1034/j.1600-0889.1999.t01-4-00004.x

CO emissions from degrading plant matter: (II). Estimate of a global source strength

Abstract: From relationships between integrated daily CO emissions and received solar radiation obtained for different standing dead grasses in field experiments in a savanna region in South Africa, and making use of ecosystem and solar irradiation databases, we derive estimates on global CO production and seasonality from photochemical decay of dry grasses and litter. The photochemical CO source strength from standing dead plant material and litter in various grassland ecosystems and deciduous forests ranges from 20 to 65 Tg CO per year (1 Tg = 10 12 g). Accounting for potentially CO emitting ecosystems not included in the data set, we estimate that 60 ± 30 Tg of CO are annually emitted by photochemical degradation of decaying plant matter, mostly in the tropics. We further estimate thermal CO production from the global topsoil non-woody litter pool on the basis of global climate data and measured Arrhenius parameters to add another 40 Tg CO per year, much depending on the chosen parameters, and probably uncertain by a factor of 2. The total global source of CO by these mechanisms may thus be in the range 100 +70 −50 Tg CO per year. Although the estimated CO source strength is a relatively small contribution to the global CO budget (2–8%), CO emissions may significantly compensate for CO deposition on soils in the tropics during certain times of the year. Currently, modelling studies mostly impose a constant CO deposition velocity from the atmosphere to the soil surface, based generally on measurements on bare soil. Future modelling efforts may need to include geographical and photochemical factors which play a role in CO exchange in tropical ecosystems. DOI: 10.1034/j.1600-0889.1999.t01-4-00004.x

Short‐term variations in the 13C/12C ratio of CO as a measure of Cl activation during tropospheric ozone depletion events in the Arctic

Abstract: Analyses of the CO stable isotopic composition in surface air samples collected at high northern latitudes during Arctic spring reveal significant depletions in the 13C content of atmospheric CO, which coincide with episodes of tropospheric O3 loss. This isotope signal can be explained by production of small amounts of highly 13C-depleted CO, formed in Cl-initiated oxidation of CH4 due to the presence of enhanced Cl levels during O3 depletion events. Using the recently measured fractionation factor for the CH4 + Cl reaction, the observed 13C depletion is employed to estimate the time-integrated amount of Cl radicals encountered by the O3 depleted air mass. The results support findings obtained from measurements of hydrocarbon mixing ratios during O3 depletion events. The 13C content of atmospheric CO can thus be used as a sensitive indicator for enhanced Cl radical levels in the atmosphere.

The Upper Stratospheric Ozone Budget: An Update of Calculations Based on HALOE Data

Abstract: On the basis of data obtained by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) box model calculations are performed to investigate the ozone budget in the upper stratosphere. The HALOE data comprise measurements of major source gases and key chemical species involved in the ozone destruction cycles. In comparison to earlier calculations using version 17 of the HALOE data, the calculated ozone destruction rate increases when the updated data version 18 is used. However, as with the previous study using version 17 of the HALOE data, no evidence for a significant model ozone deficit is found.

Chemical ozone loss in the Arctic vortex in the winter 1995–96: HALOE measurements in conjunction with other observations

Abstract: Severe chemical ozone loss has been detected in the Arctic in the winter and spring of 1995-96 by a variety of methods. Extreme reductions in column ozone due to halogen catalysed chemistry were derived from measurements of the Halogen Occultation Experiment (HALOE) on board the Upper Atmosphere Research Satellite in the Arctic vortex. Here, we discuss further aspects of the HALOE observations in the Arctic over this period. Potential problems, both in the data themselves and in the methodology of the data analysis are considered and the reason for the differences between the Arctic ozone losses deduced from HALOE data version 17 and 18 is analysed. Moreover, it is shown that HALOE measurements in the Arctic in winter and spring 1995-96 compare well with observations by other ground-based and satellite instruments.

Actinic fluxes and photodissociation coefficients in cloud fields embedded in realistic atmospheres

Abstract: The spatial distribution of the actinic flux is investigated for a realistic scattering and absorbing atmosphere with embedded two-dimensional (2-D) clouds. Three different models are intercompared for computing the actinic flux: MCC4, a versatile Monte Carlo code, SHDOM, a freely available code for solving the multidimensional integral form of the radiative transfer equation, and DISORT, a widely used discrete ordinate code for plane-parallel media. Three different cloud scenarios are chosen; plane-parallel clouds, internally homogeneous rectangular cloud bands, and a realistically variable stratocumulus cloud field. For scattered cloud fields the results show that both Rayleigh scattering as well as ground reflection significantly smooth out the actinic flux field. For cloud fields with realistic spatially inhomogeneous liquid water distributions, local maxima of the actinic flux are strongly correlated with the corresponding maxima in cloud water. The spatial patterns of the actinic flux field as computed with MCC4 and SHDOM agree very well. The horizontally averaged flux results of MCC4 and SHDOM are within 1–2% of each other. For the 2-D cloud cases considered, SHDOM turned out to be 1 to 2 orders of magnitude faster than MCC4. For the stratocumulus cloud photodissociation coefficients for NO2 and O(1D) were computed with SHDOM and compared with the plane-parallel (PP), independent pixel (IP), and locally smoothed IP (SIP) approximations. The PP is characterized by a general underestimation of the photodissociation coefficients in and below the cloud, whereas the IP reproduces horizontal averages satisfactorily well. Local biases of the IP near cloud top can be significantly reduced by employing the SIP.

Parameters for global ecosystem models

Abstract: Tian et al1 have used their process-based ecosystem model to estimate the net CO2exchanges, also called net ecosystem productivity, for the years 1980-94 They deduced a large interannual variability ranging between −02 (from land to atmosphere) and +07 petagrams of carbon (Pg C) per year, the variability being mostly a function of soil moisture, which in turn is largely regulated by precipitation and temperature These values were derived by including the modelled effects of increasing atmospheric levels of CO2 The above numbers are the differences between net primary productivity and heterotrophic respiration Over the given time period for the CO2feedback case, these values were 50 (±03) and 48 (±01) Pg C per year, respectively The calculated net ecosystem productivity was thus a small fraction, between −4% and +14%, of the net primary productivity, with an average over the 15-year period of +4%

The global effects of Asian haze [air pollution]

Abstract: The authors describe how a thick layer of aerosols just discovered above the Indian Ocean by an international team may be a far-reaching influence on climate systems. The layer of haze was the discovery of the Indian Ocean Experiment (Indoex), an international field experiment that has been collecting surface and atmospheric data over the tropical Indian Ocean since 1996.

Global Problems of Atmospheric Chemistry — The Story of Man’s Impact on Atmospheric Ozone

Abstract: As early as 1930 Sydney Chapman had proposed that the formation of “odd oxygen” Ox (= O, O3) is due to photolysis of O2 by solar radiation at wavelengths shorter than 240 nm: $$\begin{array}{*{20}{c}} {{{O}_{2}} + hv \to 2O} & {(\lambda \leqslant 240nm).} \\ \end{array}$$ (1.1)