E. Reimer

Prolonged stratospheric ozone loss in the 1995–96 Arctic winter

It is well established that extensive depletion of ozone, initiated by heterogenous reactions on polar stratospheric clouds (PSCs) can occur in both the Arctic and Antarctic lower stratosphere. Moreover, it has been shown that ozone loss rates in the Arctic region in recent years reached values comparable to those over the Antarctic,. But until now the accumulated ozone losses over the Arctic have been the smaller, mainly because the period of Arctic ozone loss has not—unlike over the Antarctic—persisted well into springtime. Here we report the occurrence—during the unusually cold 1995–96 Arctic winter—of the highest recorded chemical ozone loss over the Arctic region. Two new kinds of behaviour were observed. First, ozone loss at some altitudes was observed long after the last exposure to PSCs. This continued loss appears to be due to a removal of the nitrogen species that slow down chemical ozone depletion. Second, in another altitude range ozone loss rates decreased while PSCs were still present, apparently because of an early transformation of the ozone-destroying chlorine species into less active chlorinenitrate. The balance between these two counteracting mechanisms is probably a fine one, determined by small differences in wintertime stratospheric temperatures. If the apparent cooling trend in the Arctic stratosphere is real, more dramatic ozone losses may occur in the future.

Chemical depletion of Arctic ozone in winter 1999/2000

During Arctic winters with a cold, stable stratospheric circulation, reactions on the surface of polar stratospheric clouds (PSCs) lead to elevated abundances of chlorine monoxide (ClO) that, in the presence of sunlight, destroy ozone. Here we show that PSCs were more widespread during the 1999/2000 Arctic winter than for any other Arctic winter in the past two decades. We have used three fundamentally different approaches to derive the degree of chemical ozone loss from ozonesonde, balloon, aircraft, and satellite instruments. We show that the ozone losses derived from these different instruments and approaches agree very well, resulting in a high level of confidence in the results. Chemical processes led to a 70% reduction of ozone for a region ∼1 km thick of the lower stratosphere, the largest degree of local loss ever reported for the Arctic. The Match analysis of ozonesonde data shows that the accumulated chemical loss of ozone inside the Arctic vortex totaled 117 ± 14 Dobson units (DU) by the end of winter. This loss, combined with dynamical redistribution of air parcels, resulted in a 88 ± 13 DU reduction in total column ozone compared to the amount that would have been present in the absence of any chemical loss. The chemical loss of ozone throughout the winter was nearly balanced by dynamical resupply of ozone to the vortex, resulting in a relatively constant value of total ozone of 340 ± 50 DU between early January and late March. This observation of nearly constant total ozone in the Arctic vortex is in contrast to the increase of total column ozone between January and March that is observed during most years.

Chemical Ozone Loss in the Arctic Winter 1994/95 as Determined by the Match Technique

The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (∼36 %).

Platinum group elements (Pt, Pd, Rh) in airborne particulate matter in rural vs. urban areas of Germany: Concentrations and spatial patterns of distribution

This study examines platinum group element concentrations (PGE) (i.e. platinum (Pt), palladium (Pd) and rhodium (Rh)) and their spatial distribution in airborne particulate matter fractions (PM) of human health concern in urban and rural areas of Germany. Fractionated airborne dust and PM(10), PM(2.5) and PM(1) samples were collected along a busy road in Frankfurt am Main from July 2008 to April 2010. PM(10) was also sampled in Deuselbach and Neuglobsow between January 2008 and July 2009 to examine their concentrations at rural locations and potential for long-range transport. Pt, Pd and Rh were isolated and pre-enriched in samples using a combination of Te and Hg co-precipitation methods. Concentrations were determined using isotope dilution ICP-Q-MS (in collision mode with He). The highest airborne PGE concentrations were measured in PM(10) from Frankfurt (e.g. 12.4pg Pt/m(3) (mean)), while the rural locations of Deuselbach and Neuglobsow exhibited the lowest levels (e.g. 2pg Pt/m(3) (mean)). PGE concentrations were observed to decline with increasingly smaller PM size fractions from PM(10) to PM(1). All size fractions generally contained higher levels of Pd compared to Pt and Rh, an element of greater concern due to its solubility. PM(2.5) collected in Frankfurt had a mean of 16.1pg Pd/m(3), compared to 9.4pg/m(3) for Pt. PGE concentrations also demonstrated a distinct seasonal relationship, with the greatest levels occurring in winter. Compared to a previous study in 2002, PGE concentrations in fractionated airborne dust have significantly increased over time. Elevated PGE levels were also measured for PM(10) sampled in Neuglobsow and Deuselbach, which could not be attributed to local emission sources. Using the diagnostic meteorological model, CALMET, trajectory analyses confirmed our hypothesis that PGE are being transported over longer distances from other areas of Europe.

Arctic Ozone Loss in Threshold Conditions: Match Observations in 1997/1998 and 1998/1999

Chemical ozone loss rates inside the Arctic polar vortex were determined in early 1998 and early 1999 by using the Match technique based on coordinated ozonesonde measurements. These two winters provide the only opportunities in recent years to investigate chemical ozone loss in a warm Arctic vortex under threshold conditions, i.e., where the preconditions for chlorine activation, and hence ozone destruction, only occurred occasionally. In 1998, results were obtained in January and February between 410 and 520 K. The overall ozone loss was observed to be largely insignificant, with the exception of late February, when those air parcels exposed to temperatures below 195 K were affected by chemical ozone loss. In 1999, results are confined to the 475 K isentropic level, where no significant ozone loss was observed. Average temperatures were some 8°–10° higher than those in 1995, 1996, and 1997, when substantial chemical ozone loss occurred. The results underline the strong dependence of the chemical ozone loss on the stratospheric temperatures. This study shows that enhanced chlorine alone does not provide a sufficient condition for ozone loss. The evolution of stratospheric temperatures over the next decade will be the determining factor for the amount of wintertime chemical ozone loss in the Arctic stratosphere.

A Study of Ozone Laminae Using Diabatic Trajectories, Contour Advection and Photochemical Trajectory Model Simulations.

In this paper, we show that the rate of ozone loss in both polar and mid-latitudes, derived from ozonesonde and satellite data, has almost the same vertical distribution (although opposite sense) to that of ozone laminae abundance. Ozone laminae appear in the lower stratosphere soon after the polar vortex is established in autumn, increase in number throughout the winter and reach a maximum abundance in late winter or spring. We indicate a possible coupling between mid-winter, sudden stratospheric warmings (when the vortex is weakened or disrupted) and the abundance of ozone laminae using a 23-year record of ozonesonde data from the World Ozone Data Center in Canada combined with monthly-mean January polar temperatures at 30 hPa.Results are presented from an experiment conducted during the winter of 1994/95, in phase II of the Second European Stratospheric And Mid-latitude Experiment (SESAME), in which 93 ozone-enhanced laminae of polar origin observed by ozonesondes at different time and locations are linked by diabatic trajectories, enabling them to be probed twice or more. It is shown that, in general, ozone concentrations inside laminae fall progressively with time, mixing irreversibly with mid-latitude air on time-scales of a few weeks. A particular set of laminae which advected across Europe during mid February 1995 are examined in detail. These laminae were observed almost simultaneously at seven ozonesonde stations, providing information on their spatial scales. The development of these laminae has been modelled using the Contour Advection algorithm of Norton (1994), adding support to the concept that many laminae are extrusions of vortex air. Finally, a photochemical trajectory model is used to show that, if the air in the laminae is chemically activated, it will impact on mid-latitude ozone concentrations. An estimate is made of the potential number of ozone molecules lost each winter via this mechanism.

Match observations in the Arctic winter 1996/97: High stratospheric ozone loss rates correlate with low temperatures deep inside the polar vortex

With the Match technique, which is based on the coordinated release of ozonesondes, chemical ozone loss rates in the Arctic stratospheric vortex in early 1997 have been quantified in a vertical region between 400 K and 550 K. Ozone destruction was observed from mid February to mid March in most of these levels, with maximum loss rates between 25 and 45 ppbv/day. The vortex averaged loss rates and the accumulated vertically integrated ozone loss have been smaller than in the previous two winters, indicating that the record low ozone columns observed in spring 1997 were partly caused by dynamical effects. The observed ozone loss is inhomogeneous through the vortex with the highest loss rates located in the vortex centre, coinciding with the lowest temperatures. Here the loss rates per sunlit hour reached 6 ppbv/h, while the corresponding vortex averaged rates did not exceed 3.9 ppbv/h.

Spectral analysis of air pollutants. Part 1: elemental carbon time series

An effective method to analyse different air pollution sources in an elemental carbon time series is presented. As a second feature, this technique allows a fast and efficient classification of monitoring sites. Time series of daily elemental carbon measurements at various urban locations have been evaluated with the corresponding power spectra. Typical and well-known periodicities caused by anthropogenic and meteorological influences have been identified using coherence and phase spectra. It will be shown that domestic heating by coal combustion appears as a 365 day periodicity, traffic contributes 3.5, 4.6 and 7 day peaks in the spectrum and elevated long range elemental carbon can be identified as characteristic peaks with periodicities in the range from 13 to 42 days. As the relative amplitudes of the various influences vary depending on the location of the measurement site in the urban area, the use of estimated power spectra helps to find the influence of traffic, domestic coal-heating and long range transport on the elemental carbon concentration.

An Operational Meteorological Diagnostic System for Regional Air Pollution Analysis and Long Term Modeling

A diagnostic meteorological system has been developed at the Institute for Meteorology, Freie Universitat Berlin, with the aim to calculate and analyze trajectories and meteorological synoptic patterns to determine the origin and trace of aerosols over Europe and to prepare 3-D input for air pollution transport models used within the PHOXA-program. (For a description of the PHOXA-program see Ludwig and Meinl, 1987).

Sources and Distributions of Polycyclic Aromatic Hydrocarbons and Toxicity of Polluted Atmosphere Aerosols

Levels and sources, mass size and phase distributions of parent PAHs and the toxicity of ambient aerosols at urban and rural sites of central (Czech Republic) and south-eastern (Bosnia and Hercegovina) Europe, from 2006 to 2008, are investigated. PAH pollution levels are much higher in winter than in summer, obviously due to the seasonalities of emission strength, photochemical degradation and mixing. The levels are in the range of 10–100 ng m−3 at urban and rural sites, while strong concentration gradients exist towards background sites, in particular in summer, due to both dispersion and degradation during transport. Based on back-trajectory analysis of air masses travelling to a background site in the Czech Republic, regionally significant PAH source areas were localized in eastern and south-eastern Europe, while western European countries emit less. PAHs represent a mass fraction of ≈100–500 ppm of the inhalable particulate matter (i.e. <10 μm). Based on a size resolution of 6 fractions, unimodal PAH mass size distributions were found at urban and rural sites which peaked almost exclusively in the accumulation mode (0.1–1.0 μm). Mass median diameters were found higher for semivolatile PAHs than for non volatile PAHs, probably related to re-distribution of semivolatiles in the aerosol according to the surface size distribution. Genotoxicity and AhR-mediated (i.e. dioxin-like) activity were found in all size classes at urban and rural sites in similar magnitudes. Activities were found in general highest in the fine particulate matter (i.e. <1 μm). All biological effects tested were also found in extracts of the gas-phase. PAH TEQ and antiandrogenicity were even mostly associated with gaseous pollutants. The calculated TEQ mediated by parent PAHs corresponded by average to 7.5 and 95% of the dioxin-like activity in the particulate and gaseous fractions, respectively.