Modelling long‐range transport of CFCs to Mace Head, Ireland

Self Cite

723

720

Abstract. We describe in detail the instrumentation and calibrations used in the Atmospheric Lifetime Experiment (ALE), the Global Atmospheric Gases Experiment (GAGE), and the Advanced Global Atmospheric Gases Experiment (AGAGE) and present a history of the majority of the anthropogenic ozone-depleting and climate-forcing gases in air based on these experiments. Beginning in 1978, these three successive automated high-frequency in situ experiments have documented the long-term behavior of the measured concentrations of these gases over the past 20 years, and show both the evolution of latitudinal gradients and the high-frequency variability due to sources and circulation. We provide estimates of the long-term trends in total chlorine contained in long-lived halocarbons involved in ozone depletion. We summarize interpretations of these measurements using inverse methods to determine trace gas lifetimes and emissions. Finally, we provide a combined observational and modeled reconstruction of the evolution of chlorocarbons by latitude in the atmosphere over the past 60 years which can be used as boundary conditions for interpreting trapped air in glaciers and oceanic measurements of chlorocarbon tracers of the deep oceanic circulation. Some specific conclusions are as follows: (1 are not yet at levels sufficient to contribute significantly to atmospheric chlorine loading. These replacement species could in the future provide independent estimates of the global weighted-average OH concentration provided their industrial emissions are accurately documented; (6) in the future, analysis of pollution events measured using high-frequency in situ measurements of chlorofluorocarbons and their replacements may enable emission estimates at the regional level, which, together with industrial end-use data, are of sufficient accuracy to be capable of identifying regional noncompliance with the Montreal Protocol. IntroductionCurrent concerns about the atmospheric levels of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), A third phase, the Advanced Global Atmospheric Gases Experiment (AGAGE), began over the 1993-1996 time period. AGAGE, which continues to the present, has two instrumental components. First, a highly improved gas chromatographic system measures five biogenic/anthropogenic gases [CH4, N20 , CHC13, CO, and hydrogen ( 2. The second objective is to accurately document the global distributions and temporal behavior of the biogenic/ anthropogenic gases N20 , CH4, CO, H2, CH3C1, CH3Br , and CHC13 over the globe. N20 and CH 4 are important in both the chemistry and radiative budget of the atmosphere, and changes in N20 and CH 4 may also be regarded as sensitive signals of current change in the global biosphere. CO is the major sink for OH, and both CO and CH3C1 are important indicators for regional biomass burning. Together CH3C1 and CHC13 contribute about 20% of the stratospheric chlorine content, and CH3Br contributes about 50% of bromine content [Solomon et al., 1995].3. The third objective is to optimall...

Section: Optimal Estimation Of Global Budgetsmentioning

confidence: 99%

A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE

Prinn¹,

Weiss²,

Fraser³

et al. 2000

Self Cite

723

720

“…At Mace Head, Ireland, for instance, pollution episodes caused by transport from North America are rare events, and corresponding ozone (O 3 ) enhancements are marginal [Jennings et al, 1996;Ryall et al, 1998], prompting to conclude ''that either the North American O 3 and CO plume does not intersect the European coastline over Mace Head or that this plume had become merged into the Northern Hemisphere background in transit' ' (p. 153). Similar difficulties in the definite detection of air pollution plumes from North America have been faced at other European stations, for example, at Porspoder on the French Atlantic coast [Dutot et al, 1997;Fenneteaux et al, 1999] or at Izaña on Tenerife to the west of Africa [Schmitt, 1994].…”

Section: Introductionmentioning

confidence: 99%

A backward modeling study of intercontinental pollution transport using aircraft measurements

Stohl¹,

Forster²,

Eckhardt³

et al. 2003

329

350

[1] In this paper we present simulations with a Lagrangian particle dispersion model to study the intercontinental transport of pollution from North America during an aircraft measurement campaign over Europe. The model was used for both the flight planning and a detailed source analysis after the campaign, which is described here with examples from two episodes. Forward calculations of emission tracers from North America, Europe, and Asia were made in order to understand the transport processes. Both episodes were preceded by stagnant conditions over North America, leading to the accumulation of pollutants in the North American boundary layer. Both anthropogenic sources and, to a lesser extent, forest fire emissions contributed to this pollution, which was then exported by warm conveyor belts to the middle and upper troposphere, where it was transported rapidly to Europe. Concentrations of many trace gases (CO, NO y , CO 2 , acetone, and several volatile organic compounds; O 3 in one case) and of ambient atmospheric ions measured aboard the research aircraft were clearly enhanced in the pollution plumes compared to the conditions outside the plumes. Backward simulations with the particle model were introduced as an indispensable tool for a more detailed analysis of the plume's source region. They make trajectory analyses (which, to date, were mainly used to interpret aircraft measurement data) obsolete. Using an emission inventory, we could decompose the tracer mixing ratios at the receptors (i.e., along the flight tracks) into contributions from every grid cell of the inventory. For both plumes we found that emission sources contributing to the tracer concentrations over Europe were distributed over large areas in North America. In one case, sources in California, Texas, and Florida contributed almost equally, and smaller contributions were also made by other sources located between the Yucatan Peninsula and Canada. In the other case, sources in eastern North America, including moderate contributions from forest fires, were most important. The plume's maximum was mainly caused by anthropogenic emissions from the New York area. To our knowledge, this is the first case reported where a pollution plume from a megacity was reliably detected over another continent.

“…material is lost along the warm conveyer belt [Ryall et al, 1998]. Fine time resolution is required to be able to understand the complex structure.…”

mentioning

confidence: 99%

Mechanisms for pollutant transport between the boundary layer and the free troposphere

Donnell¹,

Fish²,

Dicks³

et al. 2001

Abstract. Pollutants are longer-lived in the free troposphere than the boundary layer, hence the transport of pollutants from the boundary layer to the free troposphere has significant implications for long-range transport and global warming. It is important to quantify the transport of air between the boundary layer and the free troposphere and to understand the role different meteorological mechanisms play. Idealised passive tracer experiments, with tracer initially only in the boundary layer, are performed in a numerical model for three case study days with different synoptic conditions. After 24 hours, more than 50% of the tracer resides in the free troposphere for the two frontal cases, and 40% resides there for the high-pressure case. The tracer was transported to maximum heights of 8 km. To elucidate the role of different mechanisms for each case, the tracer amount transported by advection only, advection and turbulent mixing, and advection and convection was calculated. Advection is found to be the most important mechanism in transporting the tracer to the free troposphere; however, the addition of upright convection and turbulent mixing increases the amount by up to 24% with convection transporting the tracer to heights of 5 km. The inclusion of convection and turbulent mixing to the advection are not linearly additive processes. This study shows the possibility of a large proportion of the pollutant emitted in the boundary layer being transported to the free troposphere in a short time and the importance of representing all the meteorological processes.