1. Measurement of concentration of atmospheric gases impacting climate
at the island of Lampedusa
F. Artuso1, C. Bommarito1, P. Chamard2, A. di Sarra2, F. Monteleone1, S. Piacentino3, D. Sferlazzo3, F. Anello4
1ENEA, CLIM-OSS, Via Catania 2, Palermo, Italy; 2ENEA Casaccia, CLIM-OSS, Via Anguillarese 301, S. Maria di Galeria (Roma), Italy; 3ENEA, CLIM-OSS, Station for Climate Observations “R. Sarao”, Lampedusa, Italy; 4ENEA, PROT, Via Catania 2, Palermo, Italy 
 A program for greenhouse gases monitoring in the atmosphere was started by ENEA in 1992 at the island of Lampedusa (35.5°N, 12.6°E), in the central Mediterranean (Fig.1). The island is far from relevant anthropogenic sources, and has poor vegetation, thus is representative of the remote marine Mediterranean environment. The program began with measurements of CO2 and CH4 concentrations. In 1996 measurements of atmospheric concentration of N2O, CFC-11 and CFC-12 were also started at the Station for Climate Observation established in Lampedusa (Fig.2). A GC-MS system has been recently set up for the detection of SF6, HCFC-22, HFC-134a, HCFC-141b, and HCFC-142b in air. A system for the measurement of sulphur compounds, is also being developed to investigate the role of these species in the Mediterranean and their influence on climate.
Carbon dioxide
Measurements of the atmospheric CO2 concentration have been carried out on a weekly basis on the island of Lampedusa, in the Mediterranean, since The island is relatively far from significant carbon dioxide sources, and may be considered representative of the central Mediterranean region. The time series of carbon dioxide in the period May 1992 – May 2004 is shown in Fig.3. Some general characteristics of the series may be outlined: a progressive increase is evident, with significant yearly variations. The large annual cycle, with a maximum in early spring,, has an amplitude of approximately 10 ppmv. Relative large variation, up to 4-5 ppmv, occur on a weekly basis, and are probably associated with different origins of the sampled air masses. The CO2 behaviour at Lampedusa appears dominated by the effect of the very large 1997/1998 El Nino event. Consequently, a high negative correlation between growth rate (Fig.4) and Southern Oscillation index (Fig.5) is particularly evident for the 1997/98 period, if SOI is lagged by 9 months. This phenomenon may be explained with the weakening of the exchange with the biosphere caused by El Nino event. A correlated behaviour between the global average temperature (Fig.6) and the carbon dioxide growth rate is also found.
Methane
A similar behaviour is observed with methane data. It is the most abundant hydrocarbon in the atmosphere, and one of the most important greenhouse gases. The concentration of atmospheric methane (CH4) is measured at the Station for Climate Observations at Lampedusa since The flask samples, weekly collected, are analysed by an Agilent Technologies 6890 gas chromatograph, equipped with a flame ionisation detector (scheme in Fig. 7).
The CH4 time series, reported in Fig. 8., shows a distinct annual cycle and significant inter-annual variability. The average annual cycle has a maximum in February, and an amplitude of about 29 ppbv. The inter-annual variability is attributed to changes of emissions, possibly affected by large-scale phenomena. The methane growth rate (Fig.9) is on average close to zero during 1999 and 2000, and shows two positive peaks in 1998 and in The first peak appears to be related to El Niño/Southern Oscillation event (ENSO). The GR increases observed in 1998 and in 2001 are also believed to be due to enhanced emissions from wetlands at high northern latitudes and from the southern tropics, owing to unusual high temperatures. The highest correlation between methane GR and global temperature anomaly is 0.76, and occurs for no time lag on temperature, showing evidence that global processes strongly affect methane fluxes and distributions.
All results obtained with CH4 and CO2 data emphasize the role played by large-scale processes on the regulation of the carbon cycle.
Nitrous oxide
Nitrous oxide (N2O) is a greenhouse gas that has both natural and anthropogenic sources. Natural sources include microbial processes of nitrification and denitrification in soils and water. Anthropogenic activities like fossil fuel combustion, biomass burning, and use of fertilizers in agricolture, contribute considerably to N2O concentration increase in the atmosphere. Its global warming potential is 310 times higher than CO2. Nitrous oxide is inert in the troposphere but it plays an indirect role in the stratospheric ozone destruction. Its lifetime in the atmosphere is of 160 years.
Measurements of N2O are carried out at Lampedusa since 1996, using a gas chromatograph with an ECD detector and a packed column (see Fig.7). The concentration of N2O has slightly increased during the last years and is now around 320 ppb.
Our results are in good agreament with the N2O time series recorded at other GAW observation sites in the northern hemisphere such as Mace Head (Ireland, 53° N, 10° W) and Ryori (Japan, 39° N, 142°E).
CFC-11 and CFC-12
Chlorofluorocarbons (CFCs), which include CFC-11 and CFC-12, are greenhouse gases which have only anthropic origin. They have been used principally as refrigerant gases, as blowing agent for foams and packaging materials and solvents in industrial applications. CFCs are also responsible for the stratospheric ozone depletion phenomenon as they release chlorine in the stratosphere for photodissociation. For this reason their production has been stopped by 1996 according to the Montreal Protocol [1987] and its Amendments.
As a result, the CFC-11 and CFC-12 concentrations have started to decrease. This is confermed by the measurements in Lampedusa showing that the concentration of CFC-11 is now around 260 pptv and the CFC-12 one recently stabilized around 540 pptv. Weekly concentration of CFC-11 and CFC-12 at Lampedusa are dispayed in Fig.10.
HCFC, HFC and SF6
By the end of 1995, the production of a new family of industrial gases has been started for replacing the ozone depleting chlorofluorocarbons. These gases include hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC) and sulfur hexafluoride (SF6). They have small (HCFCs) or null (HFCs) ozone depletion potential but are powerful greenhouse gases (i.e. HFC-134a has a 100-years global warming potential of 1300 and HCFC-22 of 1700 according to the 1996 IPCC report). For this reason the detection in atmosphere of the concentration of these gases is becoming of cruccial importance.
These species are difficult to measure because of their extremely low atmospheric concentrations (few parts per trillion). A new measurement line for the detection of these atmospheric trace gases has been developed. The equipment is sited in ENEA Casaccia laboratory (Fig.11) and air sampling is performed in Lampedusa in 6L stainless steel canisters. The measurement apparatus is constituted by a preconcentration system (Markes International), able to enhance in the sample the concentration of the trace gases to be analysed, a gas chromatograph (GC 6890 Agilent Technologies) necessary for the separation of the air mixture components, and a mass spectrometer (5873N Agilent Technologies)t hat works as detector. The data recorded from the 5th of December 2003 to the 16th of July 2004 are shown in Fig.12. The Lampedusa results seem to be in line with the ones recorded at other global monitoring stations of greenhouse gases.
Dimethyl sulphide
A system for the measurement of sulphur compounds, is also being developed to investigate the role of these species in the Mediterranean and their influence on climate. Particular attention is focused on dimethyl sulphide (DMS) that is the natural precursor of most of the sulphur compounds in marine area. Such compounds, as sulphates, metansulphonic acid ecc., play an important role as cloud condensation nuclei, influencing the climate. The measurement apparatus (Fig.13) is sited in Palermo and is constituted by a calibrator (Thermo-Environmental) with a permeation oven certified at 35°C. The permeation tube (VICI Metronics) used for the production of standard mixtures of DMS has a permeation rate of 7.2 ng/min. The calibrator is connected to a preconcentration system (Markes International) which is in series with the analyser (GC 6890 Agilent Technologies). The GC is equipped with a pulsed flame photometric detector PFPD (OI Analytical) particularly suited for sulphur trace gases. The air sampling is performed in Lampedusa in 6L stainless steel canisters whose internal surface is made inert with a silcosteel layer. The set up of the DMS measurement line is still in progress.
Lampedusa
Fig.3 – Weekly CO2 concentration time series (blue line) and trend (red line).
Fig. 1 - Satellite view of Italy and Lampedusa Island (yellow arrow).
Fig.4 – CO2 growth rate vs. time. N2
Ar/CH4 25%
Carrier
FID
Out 1 2 3 4 5 6
ECD
Sample
Standard
Poraplot Q
Capillary column
Porasil B/D
Packed column
Methane
Nitrous oxide
CFC-12
CFC-11
loop
Fig.2 – View of Lampedusa ENEA Station for Climate Observations.
Fig.5 – Southern Oscillation Index (-10) time series.
Fig.7 – Scheme of the measurement apparatus for CH4, N2O, CFC-11 and CFC-12.
(a)
(c)
(b)
Fig.6 – Global temperature anomaly vs. time.
Fig.10 – Time evolution of atmospheric concentration of CH4 , N2O, CFC-11 and CFC-12 (weekly samples).
Fig.8 - Weekly CH4 concentration time series (blue line). The 12 weeks (red line) and 52 weeks (green line) running means are also reported.
Fig.12 – Time series of the concentration of SF6, HCFC-22, HFC-134a, HCFC –141b and HCFC-142b (weekly samples).
Fig.9 – CH4 growth rate vs. time.
Fig.11 – ENEA Casaccia laboratory: measurement line of HCFCs, HFC and SF6.
Fig. 13 – ENEA Palermo laboratory: measurement apparatus for sulphur compounds.