We use ozone observations from sondes, regular aircraft, and alpine surface sites in a self‐consistent analysis to determine robust changes in the time evolution of ozone over Europe. The data are ...most coherent since 1998, with similar interannual variability and trends. Ozone has decreased slowly since 1998, with an annual mean trend of −0.15 ppb yr−1 at ∼3 km and the largest decrease in summer. There are some substantial differences between the sondes and other data, particularly in the early 1990s. The alpine and aircraft data show that ozone increased from late 1994 until 1998, but the sonde data do not. Time series of differences in ozone between pairs of locations reveal inconsistencies in various data sets. Differences as small as few ppb for 2–3 years lead to different trends for 1995–2008, when all data sets overlap. Sonde data from Hohenpeissenberg and in situ data from nearby Zugspitze show ozone increased by ∼1 ppb yr−1 during 1978–1989. We construct a mean alpine time series using data for Jungfraujoch, Zugspitze, and Sonnblick. Using Zugspitze data for 1978–1989, and the mean time series since 1990, we find that the ozone increased by 6.5–10 ppb in 1978–1989 and 2.5–4.5 ppb in the 1990s and decreased by 4 ppb in the 2000s in summer with no significant changes in other seasons. It is hard to reconcile all these changes with trends in emissions of ozone precursors, and in ozone in the lowermost stratosphere. We recommend data sets that are suitable for evaluation of model hindcasts.
Key Points
Small decrease or zero trend in tropospheric ozone over Europe since late 1990s
Increases in ozone prior to late 1990s, but inconsistencies among data sets
Difficult to reconcile trends before late 1990s with known influences on ozone
Ozone (O3) profiles recorded over Beijing from 1995 to 2005 by the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program were analyzed to provide a first climatology of ...tropospheric O3 over Beijing and the North China Plains (NCPs), one of the most populated and polluted regions in China. A pooled method was adopted in the data analysis to reduce the influence of irregular sampling frequency. The tropospheric O3 over Beijing shows a seasonal and vertical distribution typical of mid-latitude locations in the Northern Hemisphere, but has higher daytime concentrations in the lower troposphere, when compared to New York City, Tokyo, and Paris at similar latitude. The tropospheric O3 over Beijing exhibits a common summer maximum and a winter minimum, with a broad summer maximum in the middle troposphere and a narrower early summer (June) peak in the lower troposphere. Examination of meteorological and satellite data suggests that the lower tropospheric O3 maximum in June is a result of strong photochemical production, transport of regional pollution, and possibly also more intense burnings of biomass in Central-Eastern China. Trajectory analysis indicates that in summer the regional pollution from the NCPs, maybe mixed with urban plumes from Beijing, played important roles on the high O3 concentrations in the boundary layer, but had limited impact on the O3 concentrations in the middle troposphere. A comparison of the data recorded before and after 2000 reveals that O3 in the lower troposphere over Beijing had a strong positive trend (approximately 2% per year from 1995 to 2005) in contrast to a flat or a decreasing trend over Tokyo, New York City, and Paris, indicating worsening photochemical pollution in Beijing and the NCPs.
Recently it was discovered that over the Middle East during summer ozone mixing ratios can reach a pronounced maximum in the middle troposphere. Here we extend the analysis to the surface and show ...that especially in the Persian Gulf region conditions are highly favorable for ozone air pollution. We apply the EMAC atmospheric chemistry-climate model to investigate long-distance transport and the regional formation of ozone. Further, we make use of available in situ and satellite measurements and compare these with model output. The results indicate that the region is a hot spot of photochemical smog where European Union air quality standards are violated throughout the year. Long-distance transports of air pollution from Europe and the Middle East, natural emissions and stratospheric ozone conspire to bring about relatively high background ozone mixing ratios. This provides a hotbed to strong and growing indigenous air pollution in the dry local climate, and these conditions are likely to get worse in the future.
In order to evaluate the observed high rural ozone levels in the eastern Mediterranean area during summertime, vertical profiles of ozone measured in the period 1994–2008 in the framework of the ...MOZAIC project (Measurement of Ozone and Water Vapor by Airbus in Service Aircraft) over the eastern Mediterranean basin (Cairo, Tel Aviv, Heraklion, Rhodes, Antalya) were analyzed, focusing in the lower troposphere (1.5–5 km). At first, vertical profiles collected during extreme days with very high or very low tropospheric ozone mixing ratios have been examined together with the corresponding back-trajectories. Also, the average profiles of ozone, relative humidity, carbon monoxide, temperature gradient and wind speed corresponding to the 7% highest and the 7% lowest ozone mixing ratios for the 1500–5000 m height layer for Cairo and Tel Aviv have been examined and the corresponding composite maps of geopotential heights at 850 hPa have been plotted. Based on the above analysis, it turns out that the lower-tropospheric ozone variability over the eastern Mediterranean area is controlled mainly by the synoptic meteorological conditions, combined with local topographical and meteorological features. In particular, the highest ozone concentrations in the lower troposphere and subsequently in the boundary layer are associated with large-scale subsidence of ozone-rich air masses from the upper troposphere under anticyclonic conditions while the lowest ozone concentrations are associated with low pressure conditions inducing uplifting of boundary-layer air, poor in ozone and rich in relative humidity, to the lower troposphere.
We use satellite sensor measurements to obtain a broad picture of the processes affecting tropical tropospheric O3 production over Africa and the Atlantic in the early part of the year. Terra/MOPITT ...CO retrievals correlate well with biomass burning fire counts observed by the TRMM/VIRS instrument in Northern Hemisphere savanna regions and allow investigation of the subsequent convection of the biomass burning plume at the intertropical convergence zone and interhemispheric transport. Measurements of NO2 from the ERS‐2/GOME instrument enable identification of two important tropical sources of this O3 precursor, biomass burning and lightning. Good correlation is seen between NO2 retrievals and TRMM/LIS lightning flash observations in southern African regions free of biomass burning, thus indicating a probable lightning source of NOx. The combination of MOPITT CO, GOME NO2, and TRMM fire and lightning flash counts provides a powerful tool for investigating the tropospheric production of O3 precursors. These data are used in conjunction with the MOZART‐2 chemical transport model to investigate the early year tropical Atlantic tropospheric O3 distribution using January 2001 as a case study. Inconsistencies between the various tropical tropospheric O3 column products obtained from EP/TOMS data, and between these products, in situ measurements, and modeling, have led to questions about how the Northern Hemisphere biomass burning is connected to the TOMS derived O3 maximum in the tropical southern Atlantic. We show that the early year tropical O3 distribution is actually characterized by two maxima. The first arises due to biomass burning emissions, is located near the Northern Hemisphere fires, and is most evident in the lower troposphere. The second is located in the southern tropical Atlantic midtroposphere, and results from NOx produced by lightning over southern Africa and South America.
Observations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local ...tropopause. The case was investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation reproduced the measurements along the flight track fairly well. A reasonable agreement with MSG observations was also achieved: the 10.8-μm brightness temperature (BT) minimum of 187 K was reproduced (a value 6 K colder than the environmental cold-point temperature) as was the positive BT difference between the 6.2- and 10.8-μm bands, an overshoot signature. The simulation produced several overshooting plumes up to 410 K yielding an upward transport of water vapour of a few tons per second across the tropical tropopause. The estimated mass flux agrees with those derived from over tracer budgets, indicating that convection transports mass across the tropopause.
The objective of this paper is to deliver the most accurate ozone (O3) and carbon monoxide (CO) climatology for the pure troposphere only, i.e. exclusively from the ground to the dynamical tropopause ...on an individual profile basis. The results (profiles and columns) are derived solely from the Measurements of OZone and water vapour by in-service Alrbus airCraft programme (MOZAIC) over 15 years (1994–2009). The study, focused on the northern mid-latitudes 24–50° N and 119° W–140° E, includes more than 40 000 profiles over 11 sites to give a quasi-global zonal picture. Considering all the sites, the pure tropospheric column peak-to-peak seasonal cycle ranges are 23.7–43.2 DU for O3 and 1.7–6.9 × 10 18 molecules cm−2 for CO. The maxima of the seasonal cycles are not in phase, occurring in February–April for CO and May–July for O3. The phase shift is related to the photochemistry and OH removal efficiencies. The purely tropospheric seasonal profiles are characterized by a typical autumn–winter/spring–summer O3 dichotomy (except in Los Angeles, Eastmed – a cluster of Cairo and Tel Aviv – and the regions impacted by the summer monsoon) and a summer–autumn/winter–spring CO dichotomy. We revisit the boundary-layer, mid-tropospheric (MT) and upper-tropospheric (UT) partial columns using a~new monthly varying MT ceiling. Interestingly, the seasonal cycle maximum of the UT partial columns is shifted from summer to spring for O3 and to very early spring for CO. Conversely, the MT maximum is shifted from spring to summer and is associated with a summer (winter) MT thickening (thinning). Lastly, the pure tropospheric seasonal cycles derived from our analysis are consistent with the cycles derived from spaceborne measurements, the correlation coefficients being r=0.6–0.9 for O3 and r>0.9 for CO. The cycles observed from space are nevertheless greater than MOZAIC for O3 (by 9–18 DU) and smaller for CO (up to 1 × 10 18 molecules cm−2). The larger winter O3 difference between the two data sets suggests probable stratospheric contamination in satellite data due to the tropopause position. The study underlines the importance of rigorously discriminating between the stratospheric and tropospheric reservoirs and avoiding use of a~monthly averaged tropopause position without this strict discrimination in order to assess the pure O3 and CO tropospheric trends.
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°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 (2–14 August 2003), compared to the periods before (16–31 July 2003) and after (16–31 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 0.3×106 ha in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NOy 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.
In this study we discuss characteristics of the Northern Hemisphere (NH) midlatitude (40°N–60°N) tropopause inversion layer (TIL) based on two data sets. First, temperature measurements from GPS ...radio occultation data (CHAMP and GRACE) for the time interval 2001–2009 are used to exhibit seasonal properties of the TIL bottom height defined here as the height of the squared buoyancy frequency minimum N2 below the thermal tropopause, the TIL maximum height as the height of the N2 maximum above the tropopause, and the TIL top height as the height of the temperature maximum above the tropopause. Mean values of the TIL bottom, TIL maximum, and TIL top heights relative to the thermal tropopause for the NH midlatitudes are (−2.08 ± 0.35) km, (0.52 ± 0.10) km and (2.10 ± 0.23) km, respectively. A seasonal cycle of the TIL bottom and TIL top height is observed with values closer to the thermal tropopause during summer. Secondly, high‐resolution temperature and trace gas profile measurements on board commercial aircrafts (Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) program) from 2001–2008 for the NH midlatitude (40°N–60°N) region are used to characterize the TIL as a mixing layer around the tropopause. Mean TIL bottom, TIL maximum, and TIL top heights based on the MOZAIC temperature (N2) measurements confirm the results from the GPS data, even though most of the MOZAIC profiles used here are available under cyclonic situations. Further, we demonstrate that the mixing ratio gradients of ozone (O3) and carbon monoxide (CO) are suitable parameters for characterizing the TIL structure.
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