Baseline Station Research Articles

Development of determination method of trace nickel in natural water by ID-oxygen added nitrogen-MIP-MS with direct measurement of liquid–liquid extracted organic phase

This work introduces the development of a novel determination method of trace nickel (ng l–1 level) in natural water samples. Nickel in the water samples is liquid–liquid extracted into methyl isobutyl ketone (MIBK) as nickel-diethyldithiocarbamate (DDTC) complex, and isotope dilution-oxygen added nitrogen-microwave induced plasma mass spectrometry (ID-oxygen added nitrogen-MIP-MS) is conducted by direct measurement of the liquid–liquid extracted organic MIBK phase. The accuracy of the proposed method was confirmed by analysing certified reference materials (NRC NASS-5 seawater, NRC SLRS-3 riverine water and NRC SLRS-4 river water), and the analytical results obtained were in good agreement with the certified values. The detection limit for nickel is 1.3 ng l−1 when the water sample is 50 times concentrated. The precision as RSD is <4%. The proposed method was applied to clarify the concentration-depth vertical profiles of nickel in Lake Mashu, Japan, as the Baseline Station of the United Nations GEMS/Water (Global Environment Monitoring System/Water) Programme.

Evaluation of in situ measurements of atmospheric carbon monoxide at Mount Waliguan, China

Abstract. Quasicontinuous measurements of carbon monoxide (CO) recorded over three years at Mount Waliguan (WLG), a global baseline station in remote western China, were examined using back trajectory analysis. The data include a revision to correct the working reference scale to the WMO2000 scale and corrections for drift in the reference gases. Between July 2004 and June 2007, CO exhibited large fluctuations and the 5 %, 50 % and 95 %-percentiles of relevant CO mixing ratios were 102 ppb, 126 ppb and 194 ppb. Approximately 50 % of all observed data were selected as CO background data using a mathematical procedure of robust local regression, with the remainder affected by regional-scale pollution. The monthly mean background CO mixing ratios showed a minimum in summer and a maximum in late winter, although all seasons were affected by short-term enhancements that exceeded background levels. The CO data were compared to values observed at the high alpine research station at Jungfraujoch, Switzerland. Smaller seasonal amplitudes were observed at WLG compared to the Jungfraujoch due to lower winter and spring CO levels, however, episodic enhancements of polluted air were greater at WLG. The air parcels arriving at WLG came predominately from the west, except in summer when advection from the east and southeast prevailed. Transport from the east or southeast typically brought polluted air to the site, having passed over populated urban areas upwind. A large number of elevated CO mixing ratios could also be associated with advection from the northwest of WLG via the central Xinjiang Uygur Autonomous Region (XUAR) and the Ge'ermu urban area where growing industrial activities as well as crops residue burning provide sources of CO. Air masses passing over northwestern Gansu were associated with relatively high CO values suggesting an anthropogenic influence, which was likely due to anthropogenic emissions from northwestern China (based on back-trajectory and potential source contribution analysis and on the INTEX-B: intercontinental Chemical Transport Experiment-Phase B). Background conditions were observed most frequently in air parcels from remote Tibet west of WLG. The probability that air parcels pass over regions of clean or polluted regions was further identified using potential source contribution function (PSCF) analysis.

Atmospheric oxygen and carbon dioxide observations from two European coastal stations 2000–2005: continental influence, trend changes and APO climatology

Abstract. Seeking for baseline conditions has biased the atmospheric carbon dioxide (CO2) and later on also oxygen (O2) monitoring networks towards remote marine stations, missing part of the variability that is due to regional anthropogenic as well as land biotic activity. We present here a five-year record of atmospheric CO2 concentrations and oxygen/nitrogen (O2/N2) ratio measurements from the coastal stations Lutjewad (LUT), The Netherlands and Mace Head (MHD), Ireland, derived from flask samples. O2/N2 ratios, a proxy for O2 concentrations, concurrently measured with CO2 concentrations, help determine regional CO2 fluxes by separating land fluxes from sea fluxes. Mace Head is the closest marine baseline station to Lutjewad, located at the same latitude, and therefore is taken as a reference. During the studied period, from 2000 until 2005, we observed an average increase of CO2 in the atmosphere of (1.7±0.2) ppm y−1, and a change of the O2/N2 ratio of (−20±1) per meg y−1. The difference between the CO2 summer minimum and the winter maximum is 14.4 ppm and 16.1 ppm at Mace Head and Lutjewad, respectively, while the paraphase variation in the O2 signal equals 113 per meg and 153 per meg, respectively. We also studied the atmospheric potential oxygen (APO) tracer at both stations. By this analysis, evidence has been found that we need to be careful when using APO close to anthropogenic CO2 sources. It could be biased by combustion-derived CO2, and models need to take into account daily and seasonal variations in the anthropogenic CO2 production in order to be able to simulate APO over the continents.

Inter-comparison of three instruments for measuring regional background carbon monoxide

Three CO instruments, i.e., vacuum ultraviolet resonance fluorescence (VUV-RF), gas chromatography/reduction gas detection (GC/RGD), and non-dispersive infrared (NDIR) spectrometry, were inter-compared at a background site, i.e., Lulin Atmospheric Baseline Station (LABS) in central Taiwan. For a period of 18 days of continuous measurements, highly coherent results were observed between the three instruments. Calibration of the GC/RGD and VUV-RF was based on the same batch of CO standards, producing results that agreed within 4%. Nevertheless, NDIR displayed a significant bias with a large offset compared to the other two instruments (about −63.1 ppb), due mainly to its over-simplified calibration procedure. The NDIR bias was then removed by aligning the NDIR data to those of GC/RGD in a process termed “post-run correction”. Through this practice, the NDIR was linked to the same calibration scale as that of GC/RGD. As a result, by simultaneously exploiting both GC/RGD and NDIR to measure background CO, both time-resolution and accuracy can be secured.

Temporal and spatial distributions of total gaseous mercury concentrations in ambient air in a mountainous area in southwestern China: Implications for industrial and domestic mercury emissions in remote areas in China

Spatial and temporal distributions of total gaseous mercury (TGM) concentrations in ambient air were investigated in the Mt. Gongga area (Sichuan province, PR China) from April 2006 to June 2007. The annual geometric mean TGM concentration at the Moxi baseline station was 3.90 ± 1.20 ng m − 3 . Geometric mean TGM concentrations at 14 representative sampling sites during the warm season ranged from 1.60 to 20.1 ng m − 3 and varied spatially, with levels decreasing between urbanized areas and more remote regions: urban area (U1–U3: 7.76 ± 4.57 to 20.1 ± 15.1 ng m − 3 ), town (T1: 4.61 ± 1.15 ng m − 3 ) and village (V1–V4: 3.26 ± 0.63 to 8.45 ± 3.06 ng m − 3 ), and remote area (R1–R6: 1.60 ± 0.43 to 3.41 ± 1.26 ng m − 3 ). Our study suggested that industrial activities, especially non-ferrous smelting activities, were an important source of atmospheric Hg and played a vital role in the regional distribution of TGM. In addition, domestic coal and biomass combustion to heat residential homes were important sources of TGM in densely populated areas during the winter months.

Lulin Atmospheric Background Station: A New High-Elevation Baseline Station in Taiwan

Lulin Atmospheric Background Station: A New High-Elevation Baseline Station in Taiwan

Representativeness and climatology of carbon monoxide and ozone at the global GAW station Mt. Kenya in equatorial Africa

Abstract. The tropics strongly influence the global atmospheric chemistry budget. However, continuous in-situ observations of trace gases are rare especially in equatorial Africa. The WMO Global Atmosphere Watch (GAW) programme aimed to close this gap with the installation of the Mt. Kenya (MKN) baseline station. Here, the first continuous measurements of carbon monoxide (CO) and ozone (O3) at this site covering the period June 2002 to June 2006 are presented. The representativeness of the site was investigated by means of statistical data analysis, air mass trajectory clustering, interpretation of biomass burning variability and evaluation of O3-CO relationships. Because of its location in eastern equatorial Africa, the site was rarely directly influenced by biomass burning emissions, making it suitable for background observations. Located at 3678 m above sea level the night-time (21:00–04:00 UTC) measurements of CO and O3 were in general representative of the free troposphere, while day-time measurements were influenced by atmospheric boundary layer air. Increased night-time concentrations were observed in 25% of all nights and associated with residual layers of increased CO and water vapour in the free troposphere. Six representative flow regimes towards Mt. Kenya were determined: eastern Africa (21% of the time), Arabian Peninsula and Pakistan (16%), northern Africa free tropospheric (6%), northern Indian Ocean and India (17%), south-eastern Africa (18%) and southern India Ocean (21%) flow regimes. The seasonal alternation of these flow regimes was determined by the monsoon circulation and caused a distinct semi-annual cycle of CO with maxima during February (primary) and August (secondary, annually variable) and with minima in April (primary) and November (secondary, annually variable). O3 showed a weaker annual cycle with a minimum in November and a broad summer maximum. Inter-annual variations were explained with differences in southern African biomass burning and transport towards MKN. Although biomass burning had little direct influence on the measurements at MKN it introduces inter-annual variability in the background concentrations of the southern hemisphere that subsequently reaches Kenya. The measurements at MKN were representative of air masses with little photochemical activity as indicated by weak O3-CO correlations, underlining the baseline character of the site. Inter-comparison of O3 at MKN with sounding data from Nairobi revealed a positive offset of the sounding data, most likely due to additional photochemical production of O3 in the Nairobi city plume. Future extensions of the measurement programme will provide better understanding of the atmospheric chemistry of this globally important region.

Aerosol optical properties and their radiative effects in northern China

As a fast developing country covering a large territory, China is experiencing rapid environmental changes. High concentrations of aerosols with diverse properties are emitted in the region, providing a unique opportunity for understanding the impact of environmental changes on climate. Until very recently, few observational studies were conducted in the source regions. The East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST‐AIRE) attempts to characterize the physical, optical and chemical properties of the aerosols and their effects on climate over China. This study presents some preliminary results using continuous high‐quality measurements of aerosol, cloud and radiative quantities made at the first EAST‐AIRE baseline station at Xianghe, about 70 km east of Beijing over a period of one year (September 2004 to September 2005). It was found that the region is often covered by a thick layer of haze (with a yearly mean aerosol optical depth equal to 0.82 at 500 nm and maximum greater than 4) due primarily to anthropogenic emissions. An abrupt “cleanup” of the haze often took place in a matter of one day or less because of the passage of cold fronts. The mean single scattering albedo is approximately 0.9 but has strong day‐to‐day variations with maximum monthly averages occurring during the summer. Large aerosol loading and strong absorption lead to a very large aerosol radiative effect at the surface (the annual 24‐hour mean values equals 24 W m−2), but a much smaller aerosol radiative effect at the top of the atmosphere (one tenth of the surface value). The boundary atmosphere is thus heated dramatically during the daytime, which may affect atmospheric stability and cloud formation. In comparison, the cloud radiative effect at the surface is only moderately higher (−41 W m−2) than the aerosol radiative effect at the surface.

Anomalous high ozone concentrations recorded at a high mountain station in Italy in summer 2003

In order to evaluate the possible effects of heatwave phenomena on background O 3 concentrations, the average summer O 3 concentrations at the high mountain station of Mt. Cimone (MTC—2165 m a.s.l.) have been analyzed. In particular, at this baseline station unusually high O 3 concentrations were recorded during August 2003, when an intense heatwave (the “August heatwave”) affected Europe. During this heatwave, the highest O 3 concentrations were recorded at MTC in connection with air masses coming from continental Europe and the Po basin boundary layer as shown by three-dimensional air mass back-trajectory and mixing height analyzes. However, high O 3 concentrations were also recorded in air masses coming from the middle troposphere (above 3000 m a.s.l.), thus suggesting the presence of O 3-rich atmospheric layers over Europe. This could be due to the large extension of the mixing layer which favoured the transport of high concentrations of O 3 and its precursors to altitudes that would usually be in the free troposphere. Other than from traffic and industrial activities, a contribution to the high O 3 concentrations recorded at MTC during the August heatwave could derive from fires in the North of Italy, as suggested by a well-documented episode and supported by in situ CO 2 measurements used as non-conventional tracer for fire emissions.

The Tropospheric 14CO2 Level in Mid-Latitudes of the Northern Hemisphere (1959–2003)

A comprehensive tropospheric 14CO2 data set of quasi-continuous observations covering the time span from 1959 to 2003 is presented. Samples were collected at 3 European mountain sites at height levels of 1205 m (Schauinsland), 1800 m (Vermunt), and 3450 m asl (Jungfraujoch), and analyzed in the Heidelberg Radiocarbon Laboratory. The data set from Jungfraujoch (1986–2003) is considered to represent the free tropospheric background level at mid-latitudes of the Northern Hemisphere, as it compares well with recent (yet unpublished) measurements made at the marine baseline station Mace Head (west coast of Ireland). The Vermunt and Schauinsland records are significantly influenced by regional European fossil fuel CO2 emissions. The respective Δ14CO2 depletions, on an annual mean basis, are, however, only 5 less than at Jungfraujoch. Vermunt and Schauinsland both represent the mean continental European troposphere.

Size distributions of ionic aerosols measured at Waliguan Observatory: Implication for nitrate gas‐to‐particle transfer processes in the free troposphere

Waliguan Observatory (WO) is a land‐based Global Atmosphere Watch baseline station on the Tibetan Plateau. Size‐resolved ionic aerosols (NH4+, Na+, K+, Ca2+, Mg2+, SO42−, Cl−, NO3− CO32−, formate, acetate and oxalate), organic aerosols, black carbon and gaseous HNO3 and SO2 were measured during an intensive fall‐winter field experiment. The observational data were analyzed with a focus on the partitioning of nitrate between the gas and particle phases. Nitrate was found to exist mainly in the particle phase with a typical particulate‐to‐total nitrate ratio, i.e., NO3−(p)/(NO3−(p) + HNO3(g)), of about 0.9. It was also found that the size distribution pattern of particulate nitrate at WO varied in different samples and the amount of particulate nitrate residing in the fine mode (Dp &lt; 2.0 μm) was typically larger than or comparable with that in the coarse mode. A gas‐particle chemical equilibrium model was used to predict these particulate nitrate size distributions. The size distributions of particulate nitrate were reasonably reproduced with the model within the uncertainties caused by the detection limits. The chemical pathways for the formation of particulate nitrate at WO were analyzed with the size distributions of measured ionic aerosols. It was demonstrated that fine nitrate particles may have been produced by the reaction of gaseous nitric acid with gaseous ammonia, while coarse nitrate particles may have been generated via the condensation of nitric acid on the surface of mineral aerosols. The signature of biomass burning at WO was found to be associated with black carbon as well as the accumulation of potassium and oxalate in the fine particles.

Trace gas monitoring at the Mauna Loa Baseline Observatory using Proton-Transfer Reaction Mass Spectrometry

Real time monitoring of volatile organic compounds (VOCs) using a Proton-Transfer Reaction Mass Spectrometer was performed at the Mauna Loa Baseline Station (19.54N, 155.58W) in March/April 2001 (March 23, 2001–April 17, 2001). Mixing ratios for methanol, acetone, acetonitrile, isoprene and methyl vinyl ketone (MVK) plus methacrolein (MACR) ranged between 0.2 and 1.8, 0.2 and 1, 0.07 and 0.2, <0.02 and 0.3, and <0.02 and 0.5ppbv, respectively. Biomass burning plumes transported from South-East Asia and the Indian Subcontinent across the Pacific influenced part of the measurement campaign. ΔAcetonitrile/ΔCO and Δacetone/Δacetonitrile ratios in these cases were 1.5×10−3 to 2.5×10−3 and 2–5ppbv/ppbv, respectively. Overall Asian outflow events were not as frequent during Spring 2001 as in previous years. Methanol did not show significant correlation with CO, acetonitrile, and acetone. The abundance of acetone and CO seemed to be influenced but not dominated by biomass burning and domestic biofuel emissions.

Estimates of the Chemical Budget for Ozone at Waliguan Observatory

Waliguan Observatory (WO) is an in-land Global Atmosphere Watch (GAW) baseline station on the Tibetan plateau. In addition to the routine GAW measurement program at WO, measurements of trace gases, especially ozone precursors, were made for some periods from 1994 to 1996. The ozone chemical budget at WO was estimated using a box model constrained by these measured trace gas concentrations and meteorological variables. Air masses at WO are usually affected by the boundary layer (BL) in the daytime associated with an upslope flow, while it is affected by the free troposphere (FT) at night associated with a downslope flow. An anti-relationship between ozone and water vapor concentrations at WO is found by investigating the average diurnal cycle pattern of ozone and water vapor under clear sky conditions. This relationship implies that air masses at WO have both the FT and BL characteristics. Model simulations were carried out for clear sky conditions in January and July of 1996, respectively. The chemical characteristics of mixed air masses (MC) and of free tropospheric air masses (FT) at WO were investigated. The effects of the variation in NOx and water vapor concentrations on the chemical budget of ozone at WO were evaluated for the considered periods of time. It was shown that ozone was net produced in January and net destroyed in July for both FT and MC conditions at WO. The estimated net ozone production rate at WO was –0.1 to 0.4 ppbv day−1 in FT air of January, 0.0 to 1.0 ppbv day−1 in MC air of January, –4.9 to –0.2 ppbv day−1 in FT air of July, and –5.1 to 2.1 ppbv day−1 in MC air of July.

Werner Lindinger

The scientific community lost a great friend and colleague with the tragic drowning of Werner Lindinger on Kauai, Hawaii, on 16 February 2001. He was a pioneer in the study of ion–molecule interactions.Werner was born in Brixlegg in the Austrian Tirol on 25 January 1944. In 1963, he enrolled at the University of Innsbruck, where he received his PhD in physics in 1972. His doctoral thesis was on the mass spectrometry of ions sampled from the negative glow plasma in a cylindrical hollow cathode. From 1967 to 1972, Werner was a part-time teaching assistant at the University of Innsbruck’s Institute of Atomic Physics. In 1972, he accepted a tenure track position at the institute.In 1973, Werner initiated his professional career as a Max Kade Foundation postdoctoral exchange fellow in the aeronomy laboratory of the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, where he remained until 1975. His considerable talent and exceptional energy led to an extremely productive period there. He rigorously exploited the newly developed flowing afterglow technology for the measurement of thermal and low-energy ion–molecule interactions, ion mobilities, and ion reactions with mainly neutral molecules.Werner returned to the physics faculty at the University of Innsbruck in 1975. He was instrumental in developing an atomic and ion physics program that quickly achieved international recognition and led to a professorship in 1978 at the Institute of Experimental Physics in Innsbruck. Werner’s group made important contributions to ion–molecule reaction kinetics and a variety of ion–molecule interaction processes, and original contributions to thermochemistry. A notable example is their series of studies of molecular–ion vibrational quenching in neutral collisions. Those detailed studies led to greatly increased understanding of the mechanistic processes involved.In later years, Werner’s interests broadened from gaseous electronics. His group extended the application of ion flow systems to supersensitive detection of trace gases in an online, real-time manner in the 1980s by using ion–molecule reaction mass spectrometry (IMR-MS) based on charge exchange reactions and, in the 1990s, by using the proton transfer reaction mass spectrometry (PTR-MS) technique. Werner and his colleagues pioneered its use in a variety of applications in medicine and food analyses, and its use in highly time-resolved studies of the emissions from vegetation and biomass burning to the atmosphere. Many research groups around the world are now applying this technique for studies of biosphere–atmosphere interactions. At the time of his death, Werner was in Hawaii to install his instrument at the NOAA Clean Air Baseline Station on Mauna Loa.Werner lectured widely in Europe and the US for many years. He was a guest professor at the University of Trento in Italy and the University of Utah, Salt Lake City. His outstanding research on the measurement of thermal and low-energy ion–molecule interactions, ion mobilities, and ion reactions with primarily neutral molecules earned him, early in his career, the Fritz Kohlrausch Prize, the Austrian Physical Society’s most prestigious award, in 1976. His scientific achievement was recognized in 1997 with Austria’s highest science award, the Erwin Schrödinger Prize of the Austrian Academy of Science.Werner’s interests were broad and varied. He had a lively appreciation of art and music. He was a vigorous person physically. Like many Tiroleans, he was an accomplished skier. He also was an avid hiker and a regular tennis player. In later years, he became a serious equestrian, riding in two African safaris.Werner’s warm and outgoing personality led to the formation of many deep friendships in Boulder, many persisting actively throughout his life. He had friends not only at NOAA, but also at JILA and the University of Colorado’s chemistry department. Werner’s extraordinary joy of living made his friendship a rewarding and memorable experience. He will be sorely missed. Werner Lindinger PPT|High resolution© 2001 American Institute of Physics.

Multi-elemental methods for fine particle source apportionment at the global baseline station at Cape Grim, Tasmania

Four standard IBA methods have been used to quantify and characterise fine particles (PM2.5) collected at the global baseline station at Cape Grim in north western Tasmania over the period 1992–1998. The methods are multi-elemental, sensitive and very fast enabling hundreds of filter papers to be analysed in a short time, with high sensitivity and source apportionment to be determined.

Non‐sea‐salt sulfate, methanesulfonate, and nitrate aerosol concentrations and size distributions at Cape Grim, Tasmania

We collected weekly aerosol samples using high‐volume impactors over a period of 20 months (1988–1990) at the Cape Grim baseline station on the northwestern coast of Tasmania, Australia. The samples were analyzed for soluble ionic constituents, including sulfate, methanesulfonate (MS−), ammonium, nitrate, and the major sea‐salt ions. The sea‐salt component showed only a slight seasonal variation, whereas the non‐sea‐salt (nss) ions all had pronounced summer maxima. Significant interannual variability was seen between the nss ion concentrations measured during the two summers investigated. Nss sulfate and MS− were present both in the fine and coarse aerosol fractions, in the latter presumably associated with sea‐salt particles. During the winter period, there was more nss sulfate in the coarse fraction than in the fine fraction. These observations are consistent with an important role of liquid‐phase oxidation in haze and cloud droplets for the production of nss sulfate aerosol. The seasonal behavior of the sulfur and nitrogen species at Cape Grim and their mutual correlations suggest that DMS oxidation is the dominant sulfur source during summer, while nonbiogenic sulfur sources make significant contributions to nss sulfate outside of this season. Correlations of CN and CCN concentrations with nss sulfate, MS−, and wind speed suggest that DMS oxidation and, to a lesser extent, seaspray formation contributes to CN and CCN populations. The contrast between the weak seasonality of the sea‐salt component and the pronounced seasonal behavior in both sulfur species and CCN supports the central role of biogenic DMS emissions as precursors of CCN in this region, at least in the biologically productive season.

Long‐range transport of anthropogenic aerosols to the National Oceanic and Atmospheric Administration baseline station at Mauna Loa Observatory, Hawaii

Size‐segregated measurements of aerosol mass and composition are used to determine the composition and seasonal variations of natural and anthropogenic aerosols at Mauna Loa Observatory (MLO) from 1993 through 1996. Although the springtime transport of Asian dust to MLO is a well‐documented phenomenon, this study shows that fine anthropogenic aerosols, including sulfur, black carbon, and enriched trace metals such as As, Cu, Pb, and Zn, are also routinely transported to MLO each spring. It is estimated that at least one third of the sulfate measured at MLO during the spring is anthropogenic. In addition, indirect measurements indicate that the organic aerosol concentrations are often comparable to the sulfate concentrations. This study also combines size‐ and time‐resolved aerosol composition measurements with isentropic, backward air‐mass trajectories and gas measurements of 222Rn, CH4, CO, and CO2 to identify some potential source regions of the anthropogenic aerosols. Three types of long‐range transport episodes are identified: (1) anthropogenic aerosols mixed with Asian dust, (2) Asian pollution with relatively small amounts of soil dust, and (3) biomass burning emissions from North America. This study shows that anthropogenic aerosols and gases can be efficiently transported to MLO from both Asia and North America during the spring.

Interstation prediction of ocean water levels using methods of nonlinear dynamics

We describe prediction of ocean water levels between geographically separated locations by using a method derived from studies of chaotic dynamical systems. This interstation predictor requires only previously observed water‐level data collected simultaneously from the target and baseline water‐level measuring stations. The current observations at the baseline station are then used for making the predictions. The method is demonstrated using data from seven “tide” stations with different water level characteristics operated by the U.S. government along the U.S. southeast coast. The data are averaged over 3 min at the sensor to filter out high‐frequency motions and are reported at 6‐min intervals. Thus the recorded water levels are all ocean surface motions that occur on timescales greater than a few minutes. The predictor forms the reconstructed attractor for both stations using previously observed data. For each new observation at the baseline station, it places the corresponding state‐space vector onto the attractor for that station. A map is then derived that associates the neighborhood around that point to the corresponding temporal neighborhood of past observations at the target station. The current observation at the baseline station is then mapped to the appropriate neighborhood for the target station. This is the estimate of the water level at the target station. This method is attractive because the data requirements are simple, the computation burden is low, and there are few decisions about the parameters needed by the algorithm. The state‐space predictor compares favorably to traditional methods including statistical correlation, cross‐spectral analysis, harmonic analysis, and response analysis. Interstation predictions are important for marine navigation and other applications. The state‐space predictor can also provide an objective way of locating tide stations, quantifying the spatial variability of ocean water levels, and identifying regions where ocean water level dynamics are similar.

Stratosphere-troposphere exchanges: case studies recorded at Mt. Cimone during VOTALP project

In order to point out and study transports of ozone rich air masses in the lower troposphere from the stratosphere/upper troposphere, continuous measurements of several parameters have been undertaken at Mt. Cimone during the European Community VOTALP project (Vertical Ozone Transport in the Alps). Several high values of surface ozone concentration due to vertical stratospheric-tropospheric exchanges have been recorded in the four mountain peak stations involved in this project (Jungfraujoch, Sonnblick, Zugspitze and Mt. Cimone) in 1996–1997. This paper presents and analyses data concerning the Mt. Cimone ground-based station, which is the highest peak of the Italian Northern Apennines and the most representative WMO-GAW site in Italy. Episodes of vertical exchange in the lower stratosphere, as tropopause folding, or in the upper troposphere, as down draft transport, have been registered at Mt. Cimone since March 1996 and subsequently studied. In fact, the comparison between the behaviours of different background trace gases at a mountain baseline station, the weather situations and the backward trajectory analyses can bring to light these events and be very useful for a better knowledge of transport phenomena. Correlation between high level of ozone concentration, chemical and meteorological parameters and three-dimensional backward trajectories relative to two particular events are herein presented.

Atmospheric carbon dioxide and its stable isotope ratios, methane, carbon monoxide, nitrous oxide and hydrogen from Shetland Isles

Since November 1992, 0.5 l glass flasks have been filled approximately monthly with dry marine air from Shetland Isles, Scotland (60.2°N, 1.2°W) and transported to CSIRO, Australia for analyses. The Shetland site is part of a CSIRO global flask network with 10–12 sites, anchored to continuous high precision in situ measurements made at the Australian Cape Grim Baseline Station (40.7°S, 144.7°E), a primary station in the Global Atmosphere Watch programme (GAW) coordinated by the World Meteorological Organisation. The methodology is summarised, and Shetland results for CO 2, CH 4, N 2O, CO, H 2 and δ 13C, δ 18O of CO 2 presented for the period 1992–1996. We compare data to available results from surrounding stations of the NOAA cooperative network (in particular Mace Head, Ireland, 53.3°N, 9.9°W), and address issues of both trace species intercalibration and atmospheric spatial gradients. While considerable uniformity of trace-gas composition is evident in oceanic air over a 13° range of latitude, nevertheless anomalies in CO 2 concentration and isotopic composition are suggested in samples representing air to the west of Shetland. The potential for remotely monitoring integrated emissions from northern Europe is also identified.