Historical and projected emissions of major halocarbons in China

The halocarbons studied here are chemicals controlled in the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer and its Amendments, which have both high ozone depleting potentials (ODPs) and high global warming potentials (GWPs). These halocarbons are mainly used for refrigeration, air-conditioning, foam blowing, tobacco expansion, aerosol propulsion, solvent cleaning, and fire fighting. China ratified the Montreal Protocol in 1991 and has been implementing the phase-out of halocarbons since then. In this paper, the emissions of halocarbons from China were estimated for 1995–2024 based on the historical consumption, the country program for complying with the Montreal Protocol, and the sector plans for phasing out halocarbons. The results show that China's compliance with the Montreal Protocol contributes greatly to both ozone protection and climate protection.     

The seasonal cycles and photochemistry of C2–C5 alkanes at Mace Head

Continuous in-situ measurements of NMHCs at Mace Head, Ireland during two full annual cycles from January 2005 to January 2007 were used to investigate NMHC emission sources and transport including dilution and photochemical oxidation. The Mace Head research station is ideally located to sample a wide range of air masses including polluted European transport, clean North Atlantic and Arctic air masses and the ultra-clean, Southern Atlantic air masses. The variety in air mass sampling is used to investigate interaction of emissions, transport, dilution and photochemistry. Variability of long-lived hydrocarbon ratios is used to assess and estimate typical transport times from emission source to the Mace Head receptor. Seasonality in the ratios of isomeric alkane pairs (for butane and pentanes) are used to assess the effects of atmospheric transport and photochemical ageing. Finally, the natural logarithms of NMHC ratios are used to assess photochemical oxidation.     

Black carbon aerosol and carbon monoxide in European regionally polluted air masses at Mace Head, Ireland during 1995–1998

Continuous measurements of black carbon aerosol (BCA) at the Mace Head Atmospheric Research Station on the Atlantic Ocean coast of Ireland show the occurrence of dramatically elevated concentrations when regionally polluted air masses are advected to the station. These occurrences correlate well with similar elevations in carbon monoxide and a wide range of other trace gases monitored near-simultaneously with the BCA. Using daily sector allocation and a sophisticated Lagrangian dispersion model, two independent estimates of the European emission source strength of BCA that are required to explain the Mace Head observations have been made. The best estimates of the UK and European emission source strengths of BCA are 46±14 and [(482–511)±140]×10³ tonnes yr⁻¹, respectively, and these estimates compare favourably with published inventories, at least to within ±25%, though they are considerably smaller than the emissions employed in some early global climate model studies.     

Estimating source regions of European emissions of trace gases from observations at Mace Head

A technique is described for identifying probable source locations for a range of greenhouse and ozone-depleting trace gases from the long-term measurements made at Mace Head, Ireland. The Met. Office's dispersion model NAME is used to predict concentrations at Mace Head from all possible sources in Europe, then source regions identified as those which consistently lead to elevated concentrations at Mace Head. Estimates of European emissions and their distribution are presented for a number of trace gases for the period 1995–1998. Estimated emission patterns are realistic, given the nature and varied applications of the species considered. The results indicate that whilst there are limitations, useful information about source distribution can be extracted from continuous measurements at a remote site. It is probable that much improved estimates could be derived if observations were available from a number of sites. The ability to assess emissions has obvious implications in monitoring compliance with internationally agreed quota and protocols.     

Methane emissions from peat bogs in the vicinity of the Mace Head Atmospheric Research Station over a 12-year period

Methane emissions from the peat bogs in Connemara, Ireland have been inferred from the trace gas observations at the Mace Head Atmospheric Research Station using the nocturnal box method. A total of 237 local events, during April to September, over a 12-year period have been studied. Simultaneous emissions of methane, carbon dioxide and chloroform are routinely observed under nocturnal inversions with low wind speeds from the peat bogs proximal to Mace Head. Night-time deposition of ozone and hydrogen occurs concurrently with these emissions. Using the temporally correlated methane and ozone data we estimate methane emissions from each event. Simultaneous methane and chloroform emissions, together with ozone and hydrogen deposition have been characterised, leading to the estimation of methane emission rates for each event. The mean methane emission flux was found to be 400 ± 90 ng m^?2 s^?1. A strong seasonal cycle was found in the methane emission fluxes but there was little evidence of a long-term trend in the emissions from the peat bogs in the vicinity of the Mace Head station.     

Sources and source variations for aerosol at Mace Head,Ireland

The sources and source variations for aerosol at Mace Head, Ireland, were studied by applying positive matrix factorization (PMF), a variant of factor analysis, to a 5-yr data set for bulk aerosol. Signals for the following six sources were evident year round: (1) mineral dust, (2) sea salt, (3) general pollution, (4) a secondary SO₄²⁻–Se signal that is composed of both natural (marine) and pollution (coal) components, (5) ferrous industries, (6) and a second marine (possibly biogenic) source. Analyses of seasonally stratified data suggested additional sources for iodine and oil emissions but these were present only in certain seasons, respectively. The marine signal is particularly strong in winter. The main pollution transport from Europe to Mace Head occurs in May, but the influence of continental European emissions is evident throughout the year. Mineral aerosol evidently follows a transport pathway similar to that of pollution aerosol, i.e., recirculation via the westerlies brings pollutants mixed with dust to the site from nearby land, i.e., Ireland, the United Kingdom, and the Belgium, Netherlands, and Luxemburg (Benelux) region, with some inputs from Scandinavia, Western Europe, Eastern Europe, and even the Mediterranean region. Compared with Bermuda, aerosol at Mace Head has stronger marine sources (especially marine-derived secondary SO₄²⁻ and Se) but weaker crustal and oil signals. Transport across the North Atlantic, especially in winter, cannot be ruled out.     

Recent decline of methyl bromide in the troposphere

Atmospheric methyl bromide (CH₃Br) measured at a remote ground station in the Arctic (mid-1996 to early 2002) and in the free troposphere at mid-latitude (early 1999 to early 2002) showed a steady annual average decrease of 4–6%. The trend was consistent with a simulation of the response to the phase-out schedule of anthropogenic emissions under the Montreal Protocol and its amendments, suggesting that a decrease in CH₃Br abundance in the Northern Hemisphere of as much as 40% from the level of the early 1990s would be possible by the completion date of the program.     

Quantitative trace analysis of polyfluorinated alkyl substances (PFAS) in ambient air samples from Mace Head (Ireland): A method intercomparison

A method intercomparison study of analytical methods for the determination of neutral, volatile polyfluorinated alkyl substances (PFAS) was carried out in March, 2006. Environmental air samples were collected in triplicate at the European background site Mace Head on the west coast of Ireland, a site dominated by ‘clean’ westerly winds coming across the Atlantic. Extraction and analysis were performed at two laboratories active in PFAS research using their in-house methods. Airborne polyfluorinated telomer alcohols (FTOHs), fluorooctane sulfonamides and sulfonamidoethanols (FOSAs/FOSEs) as well as additional polyfluorinated compounds were investigated. Different native and isotope-labelled internal standards (IS) were applied at various steps in the analytical procedure to evaluate the different quantification strategies. Field blanks revealed no major blank problems. European background concentrations observed at Mace Head were found to be in a similar range to Arctic data reported in the literature. Due to trace-levels at the remote site, only FTOH data sets were complete and could therefore be compared between the laboratories. Additionally, FOSEs could partly be included. Data comparison revealed that despite the challenges inherent in analysis of airborne PFAS and the low concentrations, all methods applied in this study obtained similar results. However, application of isotope-labelled IS early in the analytical procedure leads to more precise results and is therefore recommended.     

Global emissions of HFC-23 estimated to year 2015

HFC-23 (trifluoromethane, fluoroform, CHF₃) is a powerful greenhouse gas that is formed at the reactor stage of the manufacture of HCFC-22 (chlorodifluoromethane, CHClF₂). The amount formed depends on the conditions used in the manufacturing process and, for individual plants, lies between 1% and 4% of the production of HCFC-22. While it is possible to reduce the formation of HFC-23 by optimising process conditions, it is not possible to eliminate its production. This requires destruction, generally by thermal oxidation. Under the Kyoto Protocol, developed countries have obligations to reduce greenhouse gas emissions and, in the developing world, there are projects under the Clean Development Mechanism for the incineration of HFC-23 waste streams. These should lead to a reduction in average global emission factors relative to production of HCFC-22. We present estimates of global production of HCFC-22 up to the year 2015 and also the calculated range of emissions of HFC-23 that may be consequences of this. In terms of the effect on climate change, the atmospheric burden of HFC-23 accumulated from emissions is calculated to contribute between 0.1% and 0.2% of the radiative forcing of climate in 2015. Annual emissions of HFC-23 would be equivalent to between 284 and 28 million tonnes of CO₂ in that year, when total anthropogenic greenhouse gas emissions are predicted to lie between 46,000 million and 59,000 million tonnes of CO₂ equivalent.     

Volcanic sulphate and arctic dust plumes over the North Atlantic Ocean

High time resolution aerosol mass spectrometry measurements were conducted during a field campaign at Mace Head Research Station, Ireland, in June 2007. Observations on one particular day of the campaign clearly indicated advection of aerosol from volcanoes and desert plains in Iceland which could be traced with NOAA Hysplit air mass back trajectories and satellite images. In conjunction with this event, elevated levels of sulphate and light absorbing particles were encountered at Mace Head. While sulphate concentration was continuously increasing, nitrate levels remained low indicating no significant contribution from anthropogenic pollutants. Sulphate concentration increased about 3.8 μg m⁻³ in comparison with the background conditions. Corresponding sulphur flux from volcanic emissions was estimated to about 0.3 TgS yr⁻¹, suggesting that a large amount of sulphur released from Icelandic volcanoes may be distributed over distances larger than 1000 km. Overall, our results corroborate that transport of volcanogenic sulphate and dust particles can significantly change the chemical composition, size distribution, and optical properties of aerosol over the North Atlantic Ocean and should be considered accordingly by regional climate models.     

Continuous observations of carbon dioxide at Mace Head,Ireland from 1995 to 1999 and its net European ecosystem exchange

A 5-yr record of continuous high-frequency carbon dioxide CO₂ observations over the 1995–1999 period for the Mace Head Atmospheric Research Station has been examined to reveal a complex interplay between local- and regional-scale sources and sinks. During the winter months, an additional CO₂ source, over and above fossil fuel combustion, is required to support the observed concentrations of CO₂ in European regionally polluted air masses. During the summer months, an additional CO₂ sink is required. Over the entire study period, the additional net European ecosystem exchange source–sink required is –0.36±0.4 Gtonne C yr⁻¹.     

Analysis of 3-year observations of CFC-11, CFC-12 and CFC-113 from a semi-rural site in China

In-situ measurements of atmospheric chlorofluorocarbons (CFCs) can be used to the assess their global and regional emissions and to check for compliance with phase-out schedules under Montreal protocol and its amendments. The atmospheric mixing ratios of CFC-11 (CCl₃F), CFC-12 (CCl₂F₂) and CFC-113 (CCl₂F–CClF₂) have been measured by an automated in-situ GC-ECDs system at the regional Chinese Global Atmosphere Watch (GAW) station Shangdianzi (SDZ), from November 2006 to October 2009. The time series for these three principal CFCs showed large episodic events and background conditions occurred for approximately 30% (CFC-11), 52% (CFC-12) and 56% (CFC-113) of the measurements. The mean background mixing ratios for CFC-11, CFC-12 and CFC-113 were 244.8 ppt (parts per trillion, 10^?12, molar) 539.6 ppt and 76.8 ppt, respectively, for 2006–2009. The enhanced CFC mixing ratios compared to AGAGE sites such as Trinidad Head (THD), US and Mace Head (MHD), Ireland suggest regional influences even during background conditions at SDZ, which is much closer to highly-populated areas. Between 2006 and 2009 background CFCs exhibited downward trends at rates of ?2.0 ppt yr^?1 for CFC-11, ?2.5 ppt yr^?1 for CFC-12 and ?0.7 ppt yr^?1 for CFC-113. De-trended 3-year average background seasonal cycles displayed small fluctuations with peak-to-trough amplitudes of 1.0 ± 0.02 ppt (0.4%) for background CFC-11, 1.3 ± 2.1 ppt (0.3%) for CFC-12 and 0.2 ± 0.4 ppt (0.3%) for CFC-113. On the other hand, during pollution periods these CFCs showed much larger seasonal cycles of 11.2 ± 10.7 ppt (5%) for CFC-11, 7.5 ± 6.5 ppt (2%) for CFC-12 and 1.0 ± 1.2 ppt (1.2%) for CFC-113, with apparent winter minima and early summer maxima. This enhancement was attributed to prevailing wind directions from urban regions in summer and to enhanced anthropogenic sources during the warm season. In general, horizontal winds from northeast showed negative contribution to atmospheric CFCs loading, whereas South Western advection (urban sector: Beijing) had positive contributions.     

Trends over a 20-year period from 1987 to 2007 in surface ozone at the atmospheric research station,Mace Head,Ireland

Hourly measurements of baseline ozone at the Mace Head Atmospheric Research Station on the Atlantic Ocean coast of Ireland are observed when unpolluted air masses are advected to the station from across the North Atlantic Ocean. Monthly mean ozone mixing ratios in baseline air masses have risen steadily during the 1980s and 1990s reaching unprecedented levels during the early months of 1999. During the 2000s, baseline ozone mixing ratios have shown evidence of decline and stabilisation. Over the entire 20-year 1987–2007 period, the trend in annual baseline ozone has been +0.31±0.12(2−σ) ppb year⁻¹ and is highly statistically significant. Trends have been highest in the spring months and lowest in the summer months, producing a significant increase in the amplitude of the seasonal cycle. Over the shorter 1995–2007 period, we demonstrate how the growth to peak in 1999 and the subsequent decline have been driven by boreal biomass burning events during 1998/1999 and 2002/2003. The 2000s have been characterised by relatively constant baseline ozone and CH₄ levels and these may be a reasonable guide to future prospects, at least in the short term.     

Reductive dechlorination of chlorofluorocarbons and hydrochlorofluorocarbons in sewage sludge and aquifer sediment microcosms

The reductive transformation of the 10 most-widely distributed fluorinated volatile compounds and of tetrachloroethene was investigated for up to 177 days under anaerobic conditions in sewage sludge and aquifer sediment slurries. Concentrations of parent compounds and of degradation products were identified by GC-MS. We observed transformation of CFC-11 to HCFC-21 and HCFC-31, of CFC-113 to HCFC-123a, chlorotrifluoroethene and trifluoroethene, of CFC-12 to HCFC-22, of HCFC-141b to HCFC-151b, and of tetrachloroethene to vinyl chloride and ethene. CFC-114, CFC-115, HCFC-142b, HFC-134a and HCFC-22 were not transformed. The results suggest that with both inocula studied here, hydrogenolysis is the primary reductive dechlorination reaction. CFC-113 was the only compound where a dichloro-elimination was observed, leading to the formation of chlorotrifluoroethene as temporal intermediate and to trifluoroethene as end product. The relative reduction rates of chlorofluoromethanes compared reasonably well with theoretical rates calculated based on thermochemical data according to the Marcus theory. Some of the accumulating HCFCs and haloethenes observed in this study are toxic and may be of practical relevance in anaerobic environments.     

Tropospheric halocompounds and nitrous oxide monitored at a remote site in the Mediterranean

Analysis of time series and trends of nitrous oxide (N₂O) and halocompounds weekly monitored at the Mediterranean island of Lampedusa are discussed. Atmospheric N₂O levels showed a linear upward growth rate of 0.78 ppb yr^?1 and mixing ratios comparable with Northern Hemisphere global stations. CFC-11 and CFC-12 time series displayed a decline consistent with their phase-out. Chlorofluorocarbons (CFCs) replacing compounds and SF₆ exhibited an increasing temporal behaviour. The most rapid growth rate was recorded for HFC-134a with a value of 9.6% yr^?1. The industrial solvents CCl₄ and CH₃CCl₃, banned by the Montreal Protocol, showed opposite trends. While CH₃CCl₃ reported an expected decay of ?1.8 ppt yr^?1, an increasing rate of 5.7 ppt yr^?1 was recorded for CCl₄ and it is probably related to its relatively long lifetime and persisting emissions. Chlorinated halomethanes showed seasonality with a maximum in early April and a minimum at the end of September. Halon-1301 and Halon-1211 displayed a decreasing trend consistent with industry emission estimates.An interspecies correlation analysis gave positive high correlations between HCFC-22 and HFC-134a (+0.84) highlighting the common extensive employment as refrigerants. Sharing sources inferred the high coupling between CH₃Cl and CH₃Br (+0.73) and between CHCl₃ and CH₂Cl₂ (+0.77). A singular strong relationship (+0.55) between HFC-134a and CH₃I suggested the influence of an unknown anthropogenic source of CH₃I.Constraining of source and sink distribution was carried out by transport studies. Results were compared with the European Environment Agency (EEA) emission database. In contrast with the emission database results, our back trajectory analysis highlighted the release of large amounts of HFC-134a and SF₆ from Eastern Europe. Observations also showed that African SF₆ emissions may be considerable. Leakages from SF₆ insulated electrical equipments located in the industrialized Northern African areas justify our observations.     

Natural chloroform emissions from the blanket peat bogs in the vicinity of Mace Head,Ireland over a 14-year period

Simultaneous chloroform (CHCl₃) emission and ozone (O₃) deposition are regularly observed under nocturnal inversions during the summer months from and to the peat bogs in the vicinity of the Mace Head Atmospheric Research Station, Connemara, Co Galway, Ireland. Emissions were estimated using the nocturnal box model applied to routine atmospheric observations collected over a 14-year period from 1995 to 2008. Strict criteria were applied in the selection of events of low wind speed, under a stable night-time inversion layer in baseline air conditions, with no transport from Europe. The mean peatland CHCl₃ flux was 2.91 μg m^?2 h^?1 with highly variable fluxes ranging from 0.44 to 12.94 μg m^?2 h^?1. These fluxes are generally larger than those reported previously for similar biomes and if representative would make a significant contribution to the global estimated source of CHCl₃. Fluxes were not strongly correlated with either atmospheric temperature or the level of precipitation. Over the 14-year period there appears to have been a small increase in overall CHCl₃ emissions, although we stress that the nocturnal box model has a number of limitations and assumptions which should be taken into account.     

An analysis of condensation nuclei levels at Mace Head,Ireland

Condensation nuclei (CN) concentrations measured at Mace Head between 1990 and 1992 are presented. The background CN concentration was found to typically range from 100 to 700 cm^-3. Concentration values were in this range for 55% of the measurement period. No seasonal cycle was observed in the CN concentration values. Concurrent equivalent black carbon (EBC) measurements are used to examine anthropogenic influences on the background CN concentration. Evidence that transatlantic air mass transport influenced the background CN concentration, contributing to increased CN and EBC levels, is shown. During polluted conditions the CN concentration was generally higher than 1000 cm^-3. The principal source for high pollution levels was European air masses arriving at the site. Very high CN concentrations, greater than 50 000 cm^-3, are attributed to local gas-to-particle conversion processes. The characteristics of a number of particle production events are considered. These show that these events are highly photochemical and occur during both clean and polluted conditions. Such production events though infrequent contributed significantly to the total aerosol number concentration.     

The history of methyl chloroform emissions: 1951–2000

A complete record of annual methyl chloroform production has been compiled by combining early estimates in the technical literature (1951–1976) with audited production data supplied by chemical manufacturers (1970–1996) and with production and consumption estimates provided by the countries party to the Montreal Protocol (1989 to the present). From this, a new and comprehensive estimate of annual emissions has been developed. However, when the atmospheric concentrations calculated from these annual emissions are compared with measured concentrations, there are significant discrepancies, particularly during recent years, that merit further examination.     

International field intercomparison measurements of atmospheric mercury species at Mace Head,Ireland

Eleven laboratories from North America and Europe met at Mace Head, Ireland for the period 11–15 September 1995 for the first international field intercomparison of measurement techniques for atmospheric mercury species in ambient air and precipitation at a marine background location. Different manual methods for the sampling and analysis of total gaseous mercury (TGM) on gold and silver traps were compared with each other and with new automated analyzers. Additionally, particulate-phase mercury (Hg_part) in ambient air, total mercury, reactive mercury and methylmercury in precipitation were analyzed by some of the participating laboratories. Whereas measured concentrations of TGM and of total mercury in precipitation show good agreement between the participating laboratories, results for airborne particulate-phase mercury show much higher differences. Two laboratories measured inorganic oxidized gaseous mercury species (IOGM), and obtained levels in the low picogram m^-3 range.     

Role of organic and black carbon in the chemical composition of atmospheric aerosol at European background sites

The mass concentrations of inorganic ions, water-soluble organic carbon, water-insoluble organic carbon and black carbon were determined in atmospheric aerosol collected at three European background sites: (i) the Jungfraujoch, Switzerland (high-alpine, PM_2.5 aerosol); (ii) K-puszta, Hungary (rural, PM_1.0 aerosol); (iii) Mace Head, Ireland (marine, total particulate matter). At the Jungfraujoch and K-puszta the contribution of carbonaceous compounds to the aerosol mass was higher than that of inorganic ions by 33% and 94%, respectively. At these continental sites about 60% of the organic carbon was water soluble, 55–75% of the total carbon proved to be refractory and a considerable portion of the water soluble, refractory organic matter was composed of humic-like substances. At Mace Head the mass concentration of organic matter was found to be about twice than that of nonsea-salt ions, 40% of the organic carbon was water soluble and the amount of highly refractory carbon was low. Humic-like substances were not detected but instead low molecular weight carboxylic acids were responsible for about one-fifth of the water-soluble organic mass. These results imply that the influence of carbonaceous compounds on aerosol properties (e.g. hygroscopic, optical) might be significant.