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.     

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.     

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.     

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH₄) and carbon dioxide (CO₂)) across air–water interface in three sites with different vegetation covers and compositions were studied and compared. CH₄ emissions from three sites were 0.62±0.36, 0.70±0.36, and 1.31±0.57 mg m⁻² h⁻¹, respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH₄ emission. CO₂ fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8±20.4, 52.2±14.1 and 3.6±26.8 mg m⁻² h⁻¹, respectively. There were an evident trend that the larger macrophyte biomass, the lower CO₂ emissions. Correlation analysis showed that in different sites, dominant plant controlled CO₂ flux across air–water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere.     

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.     

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.     

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.     

Contribution of motor vehicle emissions to organic carbon and fine particle mass in Pittsburgh, Pennsylvania: Effects of varying source profiles and seasonal trends in ambient marker concentrations

We present estimates of the vehicular contribution to ambient organic carbon (OC) and fine particle mass (PM) in Pittsburgh, PA using the chemical mass balance (CMB) model and a large dataset of ambient molecular marker concentrations. Source profiles for CMB analysis are selected using a method of comparing the ambient ratios of marker species with published profiles for gasoline and diesel vehicle emissions. The ambient wintertime data cluster on a hopanes/EC ratio–ratio plot, and therefore can be explained by a large number of different source profile combinations. In contrast, the widely varying summer ambient ratios can be explained by a more limited number of source profile combinations. We present results for a number of different CMB scenarios, all of which perform well on the different statistical tests used to establish the quality of a CMB solution. The results illustrate how CMB estimates depend critically on the marker-to-OC and marker-to-PM ratios of the source profiles. The vehicular contribution in the winter is bounded between 13% and 20% of the ambient OC (274±56–416±72 ng-C m⁻³). However, variability in the diesel profiles creates uncertainty in the gasoline–diesel split. On an OC basis, one set of scenarios suggests gasoline dominance, while a second set indicates a more even split. On a PM basis, all solutions indicate a diesel-dominated split. The summer CMB solutions do not present a consistent picture given the seasonal shift and wide variation in the ambient hopanes-to-EC ratios relative to the source profiles. If one set of source profiles is applied to the entire dataset, gasoline vehicles dominate vehicular OC in the winter but diesel dominates in the summer. The seasonal pattern in the ambient hopanes-to-EC ratios may be caused by photochemical decay of hopanes in the summer or by seasonal changes in vehicle emission profiles.     

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.     

Modeling speciated terpenoid emissions from the European boreal forest

We present the first estimates of speciated monoterpene emissions from the North European coniferous forests. Measured emission factors and emission profiles of boreal tree species (Picea abies, Pinus sylvestris, Betula pendula, Salix phylicifolia, Populus tremula, and Alnus incana) were used together with detailed satellite land cover information and meteorological data in an emission model based on the Guenther emission algorithms. The variation of the coniferous biomass within the boreal region (60°N to 70°N) was obtained from forest inventory data, and the seasonal variability of the deciduous biomass was taken into account through simple boreal climatology parameterisation. The annual biogenic emissions in the boreal zone are dominated by coniferous species, but in the summer months, the deciduous contribution to the monoterpene and isoprene emissions is considerable. Norway spruce (Picea abies) is the most important isoprene emitter in the north European boreal forests. The biogenic emission fluxes in the South boreal zone are approximately twice as high as fluxes in the North boreal zone. α- and β-pinene, carene, and cineole are the most abundant emitted terpenes, with a strong contribution of isoprene and linalool during the summer months.     

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.     

Biogeochemistry of two types of permeable reactive barriers, organic carbon and iron-bearing organic carbon for mine drainage treatment: Column experiments

Permeable reactive barriers (PRBs) are an alternative technology to treat mine drainage containing sulfate and heavy metals. Two column experiments were conducted to assess the suitability of an organic carbon (OC) based reactive mixture and an Fe⁰-bearing organic carbon (FeOC) based reactive mixture, under controlled groundwater flow conditions. The organic carbon mixture contains about 30% (volume) organic carbon (composted leaf mulch) and 70% (volume) sand and gravel. The Fe⁰-bearing organic carbon mixture contains 10% (volume) zero-valent iron, 20% (volume) organic carbon, 10% (volume) limestone, and 60% (volume) sand and gravel. Simulated groundwater containing 380 ppm sulfate, 5 ppm As, and 0.5 ppm Sb was passed through the columns at flow rates of 64 (the OC column) and 62 (the FeOC column) ml d^− 1, which are equivalent to 0.79 (the OC column) and 0.78 (the FeOC column) pore volumes (PVs) per week or 0.046 m d^− 1 for both columns. The OC column showed an initial sulfate reduction rate of 0.4 µmol g (OC)^− 1 d^− 1 and exhausted its capacity to promote sulfate reduction after 30 PVs, or 9 months of flow. The FeOC column sustained a relatively constant sulfate reduction rate of 0.9 µmol g (OC)^− 1 d^− 1 for at least 65 PVs (17 months). In the FeOC column, the δ³⁴S values increase with the decreasing sulfate concentration. The δ³⁴S fractionation follows a Rayleigh fractionation model with an enrichment factor of 21.6‰. The performance decline of the OC column was caused by the depletion of substrate or electron donor. The cathodic production of H₂ by anaerobic corrosion of Fe probably sustained a higher level of SRB activity in the FeOC column. These results suggest that zero-valent iron can be used to provide an electron donor in sulfate reducing PRBs. A sharp increase in the δ¹³C value of the dissolved inorganic carbon and a decrease in the concentration of HCO₃⁻ indicate that hydrogenotrophic methanogenesis is occurring in the first 15 cm of the FeOC column.     

Adsorption of uranium(VI) on amorphous ferric oxyhydroxide at high concentrations of dissolved carbon(IV) and sulfur(VI)

Amorphous ferric oxyhydroxide is being used to treat groundwater contaminated with uranium(VI); the compound also has potential for use as a component in in situ chemical barriers. To quantitatively evaluate its effectiveness in such applications, adsorption of uranium(VI) onto amorphous ferric oxyhydroxide was experimentally investigated under a wide range of uranium(VI) (8.40·10⁻⁷−2.10·10⁻³ mol L⁻¹; 0.2–500 mg L⁻¹), sulfur(VI) (0–0.07 mol L⁻¹; 0–2240 mg L⁻¹) and carbon(IV) (0–0.0195 mol L⁻¹; 0–234 mg L⁻¹) concentrations, and pH-values (4–9.6). The adsorption behavior of uranium(VI) (uranyl ion and its complexes) is similar to that of other cations; it exhibits a sharp rise in the extent of adsorption with increasing pH. Interactions among uranyl complexes and surface sites are interpreted using a site complexation model. Although the model does not incorporate electrostatics and includes only a single type of adsorption site, it provides a reasonable match to measured adsorption and proton exchange data. The simplicity of the model and the resulting reduction in computational demand allow its efficient incorporation into coupled reaction-transport models.     

Diurnal cycles of short-lived tropospheric alkenes at a north Atlantic coastal site

Observation of diurnal cycles in atmospheric concentrations of reactive alkenes are reported from measurements performed at a North Atlantic coastal site (Mace Head, Eire 53°19′34″N; 9°54′14″W). Species seen to exhibit distinct cycles included isoprene, ethene, propene, 1-butene, iso-butene and a substituted C₆ alkene. Five hundred and thirty air mass classified measurements were performed over a 4 week period at approximately hourly frequency and demonstrate that during periods when air flow resulted from unpolluted oceanic regions a clear daily cycle in concentrations existed, peaking at around solar noon for all species. These observations support the proposed mechanism of production via photochemical degradation of organic carbon in sea water. The observed concentrations showed strong correlation (propene R²>0.75) with solar flux, with little relationship to other meteorological or chemical parameters. The species’ short atmospheric lifetimes indicate that the source of emission was from local coastal waters within close proximity of the sampling site. At solar noon concentrations of reactive alkenes from oceanic sources were responsible for up to 88% of non-methane hydrocarbon reaction with the hydroxyl radical at this coastal marine site.     

Biomass burning losses of carbon estimated from ecosystem modeling and satellite data analysis for the Brazilian Amazon region

To produce a new daily record of gross carbon emissions from biomass burning events and post-burning decomposition fluxes in the states of the Brazilian Legal Amazon (Instituto Brasileiro de Geografia e Estatistica (IBGE), 1991. Anuario Estatistico do Brasil, Vol. 51. Rio de Janeiro, Brazil pp. 1–1024). We have used vegetation greenness estimates from satellite images as inputs to a terrestrial ecosystem production model. This carbon allocation model generates new estimates of regional aboveground vegetation biomass at 8-km resolution. The modeled biomass product is then combined for the first time with fire pixel counts from the advanced very high-resolution radiometer (AVHRR) to overlay regional burning activities in the Amazon. Results from our analysis indicate that carbon emission estimates from annual region-wide sources of deforestation and biomass burning in the early 1990s are apparently three to five times higher than reported in previous studies for the Brazilian Legal Amazon (Houghton et al., 2000. Nature 403, 301–304; Fearnside, 1997. Climatic Change 35, 321–360), i.e., studies which implied that the Legal Amazon region tends toward a net-zero annual source of terrestrial carbon. In contrast, our analysis implies that the total source fluxes over the entire Legal Amazon region range from 0.2 to 1.2 Pg C yr⁻¹, depending strongly on annual rainfall patterns. The reasons for our higher burning emission estimates are (1) use of combustion fractions typically measured during Amazon forest burning events for computing carbon losses, (2) more detailed geographic distribution of vegetation biomass and daily fire activity for the region, and (3) inclusion of fire effects in extensive areas of the Legal Amazon covered by open woodland, secondary forests, savanna, and pasture vegetation. The total area of rainforest estimated annually to be deforested did not differ substantially among the previous analyses cited and our own.     

The ratio between nitrogen oxides and carbon monoxide total emissions as precursors of tropospheric hydroxyl content evolution

The Main Geophysical Observatory 2D channel photochemical model is used to study the behavior of tropospheric OH within the 30–60°N zonal belt in relation to changing NO_X and CO emissions. The changes of tropospheric OH as a function of the contributions by NO_X and CO emissions during the period 1850–2050 are calculated. Our estimations show that the largest annual increment of total tropospheric OH within the belt considered occurs in the 1985–1995 period, about 0.27% yr⁻¹. Based on scenarios of tropospheric pollution emissions in the first half of 21st century, the total tropospheric OH content will increase more slowly, by 0.12–0.15% yr⁻¹. The maximum growth of OH concentration occurs close to air pollution locations—in the lower troposphere during 1850–1995 but in the upper troposphere in the 21st century when the NO_X source from subsonic aircraft increases faster than the surface source.     

Long-term variation of PM2.5 levels and composition at rural, urban, and roadside sites in Hong Kong: Increasing impact of regional air pollution

Long-term study of air pollution plays a decisive role in formulating and refining pollution control strategies. In this study, two 12-month measurements of PM_2.5 mass and speciation were conducted in 00/01 and 04/05 to determine long-term trend and spatial variations of PM_2.5 mass and chemical composition in Hong Kong. This study covered three sites with different land-use characteristics, namely roadside, urban, and rural environments. The highest annual average PM_2.5 concentration was observed at the roadside site (58.0±2.0 μg m⁻³ (average±2σ) in 00/01 and 53.0±2.7 μg m⁻³ in 04/05), followed by the urban site (33.9±2.5 μg m⁻³ in 00/01 and 39.0±2.0 μg m⁻³ in 04/05), and the rural site (23.7±1.9 μg m⁻³ in 00/01 and 28.4±2.4 μg m⁻³ in 04/05). The lowest PM_2.5 level measured at the rural site was still higher than the United States’ annual average National Ambient Air Quality Standard of 15 μg m⁻³. As expected, seasonal variations of PM_2.5 mass concentration at the three sites were similar: higher in autumn/winter and lower in summer. Comparing PM_2.5 data in 04/05 with those collected in 00/01, a reduction in PM_2.5 mass concentration at the roadside (8.7%) but an increase at the urban (15%) and rural (20%) sites were observed. The reduction of PM_2.5 at the roadside was attributed to the decrease of carbonaceous aerosols (organic carbon and elemental carbon) (>30%), indicating the effective control of motor vehicle emissions over the period. On the other hand, the sulfate concentration at the three sites was consistent regardless of different land-use characteristics in both studies. The lack of spatial variation of sulfate concentrations in PM_2.5 implied its origin of regional contribution. Moreover, over 36% growth in sulfate concentration was found from 00/01 to 04/05, suggesting a significant increase in regional sulfate pollution over the years. More quantitative techniques such as receptor models and chemical transport models are required to assess the temporal variations of source contributions to ambient PM_2.5 mass and chemical speciation in Hong Kong.     

Perfluorocarbon background concentrations in Europe

Five studies of the background level of several perfluorocarbon compounds in Europe are here presented together with measurements from the European Tracer Experiment (ETEX). The tracers used during the two ETEX tracer releases were the perfluorocarbons (PFCs); perfluoromethylcyclohexane (C₇F₁₄, PMCH) and perfluoromethylcyclopentane (C₆F₁₂, PMCP). Their background concentrations were detected by using both passive and active sampling techniques, to define the spatial and temporal variation of the PFCs over Europe. Also the background variations of four isomers of the PFC compound perfluorodimethylcyclohexane (C₈F₁₆, PDCH) were studied. The results were compared to other PFC tracer studies in the U.S.A. and Europe. The mean and median values of the measured PFCs were found to vary slightly and randomly in space and time. They were found to be higher and to have a larger standard deviation than the measurements from the American studies. The background concentrations were still found to be low and stable enough for PFCs to be highly suitable for use in tracer studies. The following concentrations were found: PMCP; 4.6±0.3 fl ℓ^-1, PMCH: 4.6±0.8 fl ℓ^-1, ocPDCH: 0.96±0.33 fl ℓ^-1, mtPDCH: 9.3±0.8 fl ℓ^-1, mcPDCH: 8.8±0.8 fl ℓ^-1, ptPDCH: 6.1±0.8 fl ℓ^-1. A study of the correlation between the measured PFC compounds showed a significant correlation between most of the compounds, which indicate that there are no major PFC sources in Europe.     

Global scale emission and distribution of sea-spray aerosol: Sea-salt and organic enrichment

The chemical composition of marine aerosols as a function of their size is an important parameter for the evaluation of their impact on the global climate system. In this work we model fine particle organic matter emitted by sea spray processes and its influence on the aerosol chemical properties at the global scale using the off-line global Chemistry-Transport Model TM5. TM5 is coupled to a microphysical aerosol dynamics model providing size resolved information on particle masses and numbers. The mass of the emitted sea spray particles is partitioned between water insoluble organic matter (WIOM) and sea salt components in the accumulation mode using a function that relates the emitted organic fraction to the surface ocean chlorophyll-a concentrations. The global emission in the sub-micron size range of organic matter by sea spray process is 8.2 Tg yr^?1, compared to 24 Tg fine yr^?1 sea-salt emissions. When the marine sources are included, the concentrations of modelled primary particulate organic matter (POM) increase mainly over the oceans. The model predictions of WIOM and sea salt are evaluated against measurements carried out at Mace Head (Northern Hemisphere) and Amsterdam Island (Southern Hemisphere), showing that in clean marine conditions WIOM marine emissions contribute significantly to POM values.