256 research outputs found
Evidence of tropospheric layering: interleaved stratospheric and planetary boundary layer intrusions
International audienceWe present a case study of interleaving in the free troposphere of 4 layers of non-tropospheric origin, with emphasis on their residence time in the troposphere. Two layers are stratospheric intrusions at 4.7 and 2.2 km altitude with residence times of about 2 and 6.5 days, respectively. The two other layers at 7 and 3 km altitude were extracted from the maritime planetary boundary layer by warm conveyor belts associated with two extratropical lows and have residence times of about 2 and 5.75 days, respectively. The event took place over Frankfurt (Germany) in February 2002 and was observed by a commercial airliner from the MOZAIC programme with measurements of ozone, carbon monoxide and water vapour. Origins and residence times in the troposphere of these layers are documented with a trajectory and particle dispersion model. The combination of forward and backward simulations of the Lagrangian model allows the period of time during which the residence time can be assessed to be longer, as shown by the capture of the stratospheric-origin signature of the lowest tropopause fold just about to be completely mixed above the planetary boundary layer. This case study is of interest for atmospheric chemistry because it emphasizes the importance of coherent airstreams that produce laminae in the free troposphere and that contribute to the average tropospheric ozone. The interleaving of these 4 layers also provides the conditions for a valuable case study for the validation of global chemistry transport models used to perform tropospheric ozone budgets
Classification of tropospheric ozone profiles over Johannesburg based on MOZAIC aircraft data
International audienceEach ozone profile is a unique response to the photochemical and dynamic processes operating in the troposphere and hence is critical to our understanding of processes and their relative contributions to the tropospheric ozone budget. Traditionally, mean profiles, together with some measure of variability, averaged by season or year at a particular location have been presented as a climatology. However, the mean profile is difficult to interpret because of the counteracting influences present in the micro-structure. On the other hand, case study analysis, whilst revealing, only applies to isolated conditions. In a search for pattern and order within ozone profiles, a classification based on a cluster analysis technique has been applied in this study. Ozone profiles are grouped according to the magnitude and altitude of ozone concentration. This technique has been tested with 56 ozone profiles at Johannesburg, South Africa, recorded by aircraft as part of the MOZAIC (Measurement of Ozone and Water Vapor aboard Airbus In-service Aircraft) program. Six distinct groups of ozone profiles have been identified and their characteristics described. The widely recognized spring maximum in tropospheric ozone is identified through the classification, but a new summertime mid-tropospheric enhancement due to the penetration of tropical air masses from continental regions in central Africa has been identified. Back trajectory modeling is used to provide evidence of the different origins of ozone enhancements in each of the classes. Continental areas over central Africa are shown to be responsible for the low to mid-tropospheric enhancement in spring and the mid-tropospheric peak in summer, whereas the winter low-tropospheric enhancement is attributed to local sources. The dominance of westerly winds through the troposphere associated with the passage of a mid-latitude cyclone gives rise to reduced ozone values
Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS â Part 2: Application to the global ozonesonde network
Both balloon-borne electrochemical ozonesondes and MOZAIC (measurements of
ozone, water vapour, carbon monoxide and nitrogen oxides by in-service Airbus
aircraft) provide very valuable data sets for ozone studies in the upper
troposphere/lower stratosphere (UTLS). Although MOZAIC's highly accurate
UV-photometers are regularly inspected and recalibrated annually, recent
analyses cast some doubt on the long-term stability of their ozone analysers.
To investigate this further, we perform a 16 yr comparison (1994â2009) of
UTLS ozone measurements from balloon-borne ozonesondes and MOZAIC. The
analysis uses fully three-dimensional trajectories computed from ERA-Interim
(European Centre for Medium-Range Weather Forecasts Re-analysis) wind fields
to find matches between the two measurement platforms. Although different
sensor types (Brewer-Mast and Electrochemical Concentration Cell ozonesondes)
were used, most of the 28 launch sites considered show considerable
differences of up to 25% compared to MOZAIC in the mid-1990s, followed
by a systematic tendency to smaller differences of around 5â10% in
subsequent years. The reason for the difference before 1998 remains unclear,
but observations from both sondes and MOZAIC require further examination to
be reliable enough for use in robust long-term trend analyses starting before
1998. According to our analysis, ozonesonde measurements at tropopause
altitudes appear to be rather insensitive to changing the type of the
Electrochemical Concentration Cell ozonesonde, provided the cathode sensing
solution strength remains unchanged. Scoresbysund (Greenland) showed
systematically 5% higher readings after changing from Science Pump
Corporation sondes to ENSCI Corporation sondes, while a 1.0% KI cathode
electrolyte was retained
Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data
We analyze ozone observations recorded over Equatorial Africa between April 1997 and March 2003 by the MOZAIC programme, providing the first ozone climatology deriving from continental in-situ data over this region. Three-dimensional streamlines strongly suggests connections between the characteristics of the ozone monthly mean vertical profiles, the most persistent circulation patterns in the troposphere over Equatorial Africa (on a monthly basis) such as the Harmattan, the African Easterly Jet, the Trades and the regions of ozone precursors emissions by biomass burning. During the biomass burning season in each hemisphere, the lower troposphere exhibits layers of enhanced ozone (i.e. 70 ppbv over the coast of Gulf of Guinea in December-February and 85 ppbv over Congo in June-August). The characteristics of the ozone monthly mean vertical profiles are clearly connected to the regional flow regime determined by seasonal dynamic forcing. The mean ozone profile over the coast of Gulf of Guinea in the burning season is characterized by systematically high ozone below 650hPa ; these are due to the transport by the Harmattan and the AEJ of the pollutants originating from upwind fires. The confinement of high ozone to the lower troposphere is due to the high stability of the Harmattan and the blocking Saharan anticyclone which prevents efficient vertical mixing. In contrast, ozone enhancements observed over Central Africa during the local dry season (June-August) are not only found in the lower troposphere but throughout the troposphere. Moreover, this study highlights a connection between the regions of the coast of Gulf of Guinea and regions of Congo to the south that appears on a semi annual basis. Vertical profiles in wet-season regions exhibit ozone enhancements in the lower troposphere due to biomass burning products transport from fires situated in the opposite dry-season hemisphere
Mid-latitude tropospheric ozone columns from the MOZAIC program: climatology and interannual variability
Several thousands of ozone vertical profiles collected in the course of the MOZAIC programme (Measurements of Ozone, Water Vapour, Carbon Monoxide and Nitrogen Oxides by In-Service Airbus Aircraft) from August 1994 to February 2002 are investigated to bring out climatological and interannual variability aspects. The study is centred on the most frequently visited MOZAIC airports, i.e. Frankfurt (Germany), Paris (France), New York (USA) and the cluster of Tokyo, Nagoya and Osaka (Japan). The analysis focuses on the vertical integration of ozone from the ground to the dynamical tropopause and the vertical integration of stratospheric-origin ozone throughout the troposphere. The characteristics of the MOZAIC profiles: frequency of flights, accuracy, precision, and depth of the troposphere observed, are presented. The climatological analysis shows that the Tropospheric Ozone Column (<I>TOC</I>) seasonal cycle ranges from a wintertime minimum at all four stations to a spring-summer maximum in Frankfurt, Paris, and New York. Over Japan, the maximum occurs in spring presumably because of the earlier springtime sun. The incursion of monsoon air masses into the boundary layer and into the mid troposphere then steeply diminishes the summertime value. Boundary layer contributions to the <I>TOC</I> are 10% higher in New York than in Frankfurt and Paris during spring and summer, and are 10% higher in Japan than in New York, Frankfurt and Paris during autumn and early spring. Local and remote anthropogenic emissions, and biomass burning over upstream regions of Asia may be responsible for the larger low- and mid-tropospheric contributions to the tropospheric ozone column over Japan throughout the year except during the summer-monsoon season. A simple Lagrangian analysis has shown that a minimum of 10% of the <I>TOC</I> is of stratospheric-origin throughout the year. Investigation of the short-term trends of the <I>TOC</I> over the period 1995–2001 shows a linear increase 0.7%/year in Frankfurt, 0.8%/year in Japan, 1.1%/year in New York and 1.6%/year in Paris for the reduced 1995–1999 period. Dominant ingredients of these positive short-term trends are the continuous increase of wintertime tropospheric ozone columns from 1996 to 1999 and the positive contributions of the mid troposphere whatever the season
Examination of the atmospheric conditions associated with high and low summer ozone levels in the lower troposphere over the Eastern Mediterranean
Modeling lightning-NOx chemistry on a sub-grid scale in a global chemical transport model
For the first time, a plume-in-grid approach is implemented in a chemical
transport model (CTM) to parameterize the effects of the nonlinear reactions
occurring within high concentrated NO<sub><i>x</i></sub> plumes from lightning NO<sub><i>x</i></sub>
emissions (LNO<sub><i>x</i></sub>) in the upper troposphere. It is characterized by a set
of parameters including the plume lifetime, the effective reaction rate
constant related to NO<sub><i>x</i></sub>âO<sub>3</sub> chemical interactions, and the
fractions of NO<sub><i>x</i></sub> conversion into HNO<sub>3</sub> within the plume. Parameter
estimates were made using the Dynamical Simple Model of Atmospheric Chemical
Complexity (DSMACC) box model, simple plume dispersion simulations, and the
3-D Meso-NH (non-hydrostatic mesoscale atmospheric model). In order to
assess the impact of the LNO<sub><i>x</i></sub> plume approach on the NO<sub><i>x</i></sub> and O<sub>3</sub>
distributions on a large scale, simulations for the year 2006 were
performed using the GEOS-Chem global model with a horizontal resolution of
2°âŻĂâŻ2.5°. The implementation of the LNO<sub><i>x</i></sub>
parameterization implies an NO<sub><i>x</i></sub> and O<sub>3</sub> decrease on a large scale
over the region characterized by a strong lightning activity (up to 25 and
8âŻ%, respectively, over central Africa in July) and a relative increase
downwind of LNO<sub><i>x</i></sub> emissions (up to 18 and 2âŻ% for NO<sub><i>x</i></sub> and
O<sub>3</sub>, respectively, in July). The calculated variability in NO<sub><i>x</i></sub> and
O<sub>3</sub> mixing ratios around the mean value according to the known
uncertainties in the parameter estimates is at a maximum over continental
tropical regions with ÎNO<sub><i>x</i></sub> [â33.1, +29.7]âŻppt and
ÎO<sub>3</sub> [â1.56, +2.16]âŻppb, in January, and ÎNO<sub><i>x</i></sub> [â14.3, +21]âŻppt and ÎO<sub>3</sub> [â1.18,
+1.93]âŻppb, in July, mainly depending on the determination of the
diffusion properties of the atmosphere and the initial NO mixing ratio
injected by lightning. This approach allows us (i)Â to reproduce a more
realistic lightning NO<sub><i>x</i></sub> chemistry leading to better NO<sub><i>x</i></sub> and O<sub>3</sub>
distributions on the large scale and (ii)Â to focus on other improvements to
reduce remaining uncertainties from processes related to NO<sub><i>x</i></sub> chemistry
in CTM
The influence of biogenic emissions from Africa on tropical tropospheric ozone during 2006: a global modeling study
We have performed simulations using a 3-D global chemistry-transport model to investigate the influence that biogenic emissions from the African continent exert on the composition of the troposphere in the tropical region. For this purpose we have applied two recently developed biogenic emission inventories provided for use in large-scale global models (Granier et al., 2005; LathiSre et al., 2006) whose seasonality and temporal distribution for biogenic emissions of isoprene, other volatile organic compounds and NO is markedly different. The use of the 12 year average values for biogenic emissions provided by LathiSre et al. (2006) results in an increase in the amount of nitrogen sequestrated into longer lived reservoir compounds which contributes to the reduction in the tropospheric ozone burden in the tropics. The associated re-partitioning of nitrogen between PAN, HNO3 and organic nitrates also results in a similar to 5% increase in the loss of nitrogen by wet deposition. At a global scale there is a reduction in the oxidizing capacity of the model atmosphere which increases the atmospheric lifetimes of CH4 and CO by similar to 1.5% and similar to 4%, respectively. Comparisons against a range of different measurements indicate that applying the 12 year average of LathiSre et al. (2006) improves the performance of TM4_AMMA for 2006 in the tropics. By the use of sensitivity studies we show that the release of NO from soils in Africa accounts for between similar to 2-45% of tropospheric ozone in the African troposphere, similar to 10% in the upper troposphere and between similar to 5-20% of the tropical tropospheric ozone column over the tropical Atlantic Ocean. The subsequent reduction in OH over the source regions allows enhanced transport of CO out of the region. For biogenic volatile organic C1 to C3 species released from Africa, the effects on tropical tropospheric ozone are rather limited, although this source contributes to the global burden of VOC by between similar to 2-4% and has a large influence on the organic composition of the troposphere over the tropical Atlantic Ocean
Tropospheric ozone climatology over Beijing : analysis of aircraft data from the MOZAIC program
Author name used in this publication: Wang, T.2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Air pollution during the 2003 European heat wave as seen by MOZAIC airliners
This study presents an analysis of both MOZAIC profiles above Frankfurt and Lagrangian dispersion model simulations for the 2003 European heat wave. The comparison of MOZAIC measurements in summer 2003 with the 11-year MOZAIC climatology reflects strong temperature anomalies (exceeding 4&deg;C) throughout the lower troposphere. Higher positive anomalies of temperature and negative anomalies of both wind speed and relative humidity are found for the period defined here as the heat wave (2&ndash;14 August 2003), compared to the periods before (16&ndash;31 July 2003) and after (16&ndash;31 August 2003) the heat wave. In addition, Lagrangian model simulations in backward mode indicate the suppressed long-range transport in the mid- to lower troposphere and the enhanced southern origin of air masses for all tropospheric levels during the heat wave. Ozone and carbon monoxide also present strong anomalies (both ~+40 ppbv) during the heat wave, with a maximum vertical extension reaching 6 km altitude around 11 August 2003. Pollution in the planetary boundary layer (PBL) is enhanced during the day, with ozone mixing ratios two times higher than climatological values. This is due to a combination of factors, such as high temperature and radiation, stagnation of air masses and weak dry deposition, which favour the accumulation of ozone precursors and the build-up of ozone. A negligible role of a stratospheric-origin ozone tracer has been found for the lower troposphere in this study. From 29 July to 15 August 2003 forest fires burnt around 0.3&times;10<sup>6</sup> ha in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NO<sub>y</sub> mixing ratios, advected from Portugal, were crossed by the MOZAIC aircraft in the free troposphere over Frankfurt. A series of forward and backward Lagrangian model simulations have been performed to investigate the origin of anomalies during the whole heat wave. European anthropogenic emissions present the strongest contribution to the measured CO levels in the lower troposphere (near 30%). This source is followed by Portuguese forest fires which affect the lower troposphere after 6 August 2003 and even the PBL around 10 August 2003. The averaged biomass burning contribution reaches 35% during the affected period. Anthropogenic CO of North American origin only marginally influences CO levels over Europe during that period
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