Global Residence Time Research Articles

The impact of mean sea level rise on the oceanic water exchange of a back-reef lagoon

The potential impact of the future mean sea level rise (SLR) on residence times in back-reef lagoons remains uncertain. This study employs a hydrodynamical model and a tracer model to investigate the repercussions of SLR on residence times. Two scenarios are considered: one with a growing fringing reef, maintaining a semi-closed lagoon, and the other where the fringing reef overflows due to SLR, facilitating direct cross-reef ocean water exchange. The results reveal a nuanced picture of how SLR-induced changes in fringing reef dynamics influence residence times. In the growing reef scenario, where the lagoon remains semi-closed, a decrease in residence time of less than 10% is projected under SLR scenarios. However, in the non-growing scenario with overflow, allowing direct cross-reef exchange, a substantial 20%–40% decrease in residence time compared to the present state is observed. The probability density distribution of residence times throughout the year exhibits significant differences between the two scenarios. Particularly, the non-growing reef case displays a higher probability of residence time less than 10 h. Seasonal variability in cross-reef exchange contributions is attributed to coastal monsoon winds. The onset of the summer monsoon introduces an inter-annual variability in the contribution of cross-reef exchange to lagoon-ocean water exchange. This finding has broader implications for similar coastal back-reef lagoon systems, offering insights into estimating future global changes in residence times. In summary, this study emphasises the pivotal role of SLR-induced reef changes in shaping the dynamics of lagoon-ocean water exchange. The intricate interplay between fringing reef growth and overflow under SLR scenarios significantly influences residence times, with potential implications for the broader understanding of coastal back-reef lagoon systems. The findings contribute valuable insights into the complex interactions between climate-induced sea level changes and coastal ecosystems, guiding future assessments of global residence time variations.

Reconstructing the Preindustrial Coastal Carbon Cycle Through a Global Ocean Circulation Model: Was the Global Continental Shelf Already Both Autotrophic and a CO2 Sink?

AbstractThe contribution of continental shelves to the marine carbon cycle is still poorly understood. Their preindustrial state is, for one, essentially unknown, which strongly limits the quantitative assessment of their anthropogenic perturbation. To date, approaches developed to investigate and quantify carbon fluxes on continental shelves have strongly simplified their physical and biogeochemical features. In this study, we enhance the global ocean biogeochemistry model HAMburg Ocean Carbon Cycle by explicitly representing riverine loads of carbon and nutrients, as well as improving the representation of organic matter dynamics in the coastal ocean. Our simulations, at a resolution of ∼0.4°, reveal a globally averaged shelf water residence time (RT) of 12–17 months, which is much shorter than the global RTs previously assumed in benchmark studies (>4 years). This shorter global RT, induced primarily through outer shelf regions with large oceanic inflows, promotes an efficient offshore transport of terrestrial and marine organic carbon (0.44 PgCyr−1) and a dissolved inorganic carbon sink from the organic cycling of carbon on the global shelf (net ecosystem productivity [NEP] equal to +0.20 PgCyr−1). In turn, this autotrophic state of continental shelves contributes to a weak global preindustrial sink of atmospheric CO2 (0.04 PgCyr−1), dominated by extensive regions with large oceanic inflows and positive NEPs, such as the Patagonian shelf, the East China Sea and the outer North Sea. The contemporary global shelf CO2 uptake of 0.15 PgCyr−1 furthermoresuggests that the anthropogenic CO2 uptake (0.11 PgCyr−1) on the global continental shelf is less efficient with respect to the open ocean.

Effect of Different Acoustic Parameters on NOx Emissions of Partially Premixed Flame

The effects of acoustic frequency (f)/0–400 Hz and amplitude (A)/0–1400 Pa on nitrogen oxides (NOx) emissions of a partially premixed flame were investigated experimentally. The mechanism of NOx emissions was analyzed by the evolution of the vortex, which was shown by particle image velocimetry (PIV). From the relationship of NOx emission index (EINOx) and acoustic parameters, it was concluded that a critical frequency (fc) from 170 Hz to 190 Hz appeared. When the frequency was less than fc, EINOx decreased linearly with an increase in amplitude. The flame length became shorter, which led to a decrease in the global residence time, and hence, a reduction in reaction time for NOx. However, a direct proportional relationship between EINOx and amplitude was not found when the frequency was larger than fc. Based on PIV particle scattering images, with an increase of the acoustic frequency, the effects of the acoustic field on the flame base became less significant, but the flame length and reaction space of NOx were gradually increased.

Generalization of the radiative fraction correlation for hydrogen and hydrocarbon jet fires in subsonic and chocked flow regimes

The radiative fraction is one key parameter to characterize the jet flame combustion dynamics and to calculate the thermal radiant heat emitted from jet fire. A theoretical analysis is conducted to clarify the key parameters that dominate the radiative fraction of jet fires, with discussion of the limitation of previous radiative fraction correlations. A completely new dimensionless group, consisting of the mass fraction of fuel at stoichiometric conditions, the density ratio of fuel gas to ambient air and the flame Froude number, is proposed to correlate the radiative fraction of jet fires. The current up-to-date experimental data are used to build the radiative fraction correlation that covers orifice exit diameters from one to hundreds of millimeter, hydrogen, methane and propane fuels, vertical and horizontal jets, buoyance- and momentum-controlled releases, subsonic, sonic and supersonic jets. It is found that the source Froude number can fit the radiative fraction of a particular fuel jet fire. However, the new dimensionless group can correlate the radiative fractions of fuel-different jet fires. The predictive capability of the new correlation exceeds that of previously published work based on the source Froude number only or the global residence time with/without correction factors.

An upscaled rate law for magnesite dissolution in heterogeneous porous media

Spatial heterogeneity in natural subsurface systems governs water fluxes and residence time in reactive zones and therefore determines effective rates of mineral dissolution. Extensive studies have documented mineral dissolution rates in natural systems, although a general rate law has remain elusive. Here we fill this gap by answering two questions: (1) how and to what extent does spatial heterogeneity affect water residence time and effectively-dissolving surface area? (2) what is the upscaled rate law that quantifies effective dissolution rates in natural, heterogeneous media? With data constraints from experimental work, 240 Monte-Carlo numerical experiments of magnesite dissolution within quartz matrix were run with spatial distributions characterized by a range of permeability variance σ2lnκ (0.5–6.0) and correlation length (2–50cm). Although the total surface area and global residence time (τa) are the same in all experiments, the water fluxes through reactive magnesite zones varies between 0.7 and 72.8% of the total water fluxes. Highly heterogeneous media with large σ2lnκ and long λ divert water mostly into non-reactive preferential flow paths, therefore bypassing and minimizing flow in low permeability magnesite zones. As a result, the water residence time in magnesite zones (i.e., reactive residence time τa,r) is long and magnesite dissolution quickly reaches local equilibrium, which leads to small effective surface area and low dissolution rates. Magnesite dissolution rates in heterogeneous media vary from 2.7 to 100% of the rates in the equivalent homogeneous media, with effectively-dissolving surface area varying from 0.18 to 6.83 m2 (out of 51.71 m2 total magnesite surface area). Based on 240 numerical experiments and 45 column experiments, a general upscaled rate law in heterogeneous media, RMgCO3,ht=kAe,hm1-exp-τaτa,rα, was derived to quantify effective dissolution rates. The dissolution rates in heterogeneous media are a function of the rate constants k being those measured under well-mixed conditions, effective surface area in equivalent homogeneous media Ae,hm, and the heterogeneity factor 1-exp-τaτa,rα. The heterogeneity factor quantify heterogeneity effects and depends on the relative magnitude of global residence time (τa) and reactive residence time (τa,r), as well as the shape factor α=5σlnκ2 of the gamma distribution for reactive residence times. Exponential forms of rate laws have been used at the micro-scale describing direct interactions among water and mineral surface, and at the catchment scale describing weathering rates and concentration-discharge relationships. These observations highlight the key role of mineral-water contact time in determining dissolution rates at different scales. This work also emphasizes the importance of critical interfaces between reactive and non-reactive zones as determined by the details of spatial patterns and effective surface area as a scaling factor that quantifies dissolution rates in heterogeneous media across scales.

3D simulations of a microchannel reactor with diffusion inside the catalyst layer for 1-butanol dehydration reaction in gas phase

3D and a 2D-axisymmetric models in COMSOL Multiphysics® environment were developed to address modeling strategies to optimize the performance of wall-coated microstructured reactors operated to study gas-phase reactions under isothermal conditions. The kinetics for 1-butanol dehydration reaction was derived in our previously published research. Typically ideal models are used for modelling bulk flow in the free channel with diffusion–reaction at the surface of the layer. However in order to solve the system non-idealities, we used non-ideal models to simulate the flow field inside the free channel and diffusion–reaction in the catalyst coating. The obtained results from the 3D and 2D-axisymmetric models developed in COMSOL Multiphysics® were compared mainly with 2D-PFR-type model developed in MATLAB®. The one-way coupling between the fluid flow and transport of the components revealed that flow field non-idealities effect the performance predictions for the system. The performance and efficiency of the washcoat catalyst in microstructured reactors can be improved by controlling the thickness of the catalyst layer. As a conclusion, to optimize the performance of microstructured reactors the effect of reactor flow field must also be considered besides, the other key operational parameters such as global residence time, reaction conditions and catalyst layer thickness.

Understanding the flushing capability of Bellingham Bay and its implication on bottom water hypoxia

In this study, an unstructured-grid finite-volume coastal ocean model (FVCOM) was used to simulate hydrodynamic circulation and assess the flushing capability in Bellingham Bay, Washington, USA. The model was reasonably calibrated against field observations for water level, velocity and salinity, and was further used to calculate water residence time in the study site. The model results suggest that, despite the large tidal ranges (∼4 m during spring tide), tidal currents are relatively weak in Bellingham Bay with surface currents generally below 0.5 m/s. The local water residence time in Bellingham Bay varies from near zero to as long as 15 days, depending on the location and river flow conditions. In general, Bellingham Bay is a well-flushed coastal embayment affected by freshwater discharge, tides, wind, and density-driven circulation. The basin-wide global residence time ranges from 5 to 7 days. The model results also provide useful information on possible causes of the emerging summertime hypoxia problem in the north central region of Bellingham Bay. Model results suggest that the formation of hypoxia in bottom water results from an enhanced oxygen consumption rate in the oceanic bottom water inflow with low dissolved oxygen by organic matters accumulated at the regions characterized with relatively long residence time in summer months.

Numerical investigation of the time-related properties of solid phase in a 3-D spout-fluid bed

Numerical simulation of the two-phase flow in a 3-D spout-fluid bed is carried out to investigate the time-related properties of solid phase based on the In-house code by CFD–DEM coupling approach. The mixing time, distribution properties of the cycle time, global residence time and local residence time of solid phase are explored. Moreover, the influences of spouting gas velocity, background velocity, particle diameter and bed thickness on these properties are discussed. The results illustrate that the mixing time is lowered with the increase of spouting velocity or the decrease of background velocity. Cycle time shows a log-normal distribution behavior and grows with the increase of the particle diameter but decreases with the increase of spouting velocity or background velocity. Moreover, nearly 60% of the total particle time elapses in the annulus and 34% of that in the fountain while only 6% of that is paid in the spout. The solid residence time (SRT) in the spout or annulus diminishes with increasing spouting velocity or background velocity and also the decrease of particle diameter. However, the SRT in the fountain region shows the opposite response behavior. The scale-up of the bed thickness enlarges the cycle time and SRTs in three regions of the bed. Besides, small local SRT appears in the spout while large value exists in the annulus especially the corners of the bed bottom. The geometrical configuration of the bottom leads to the opposite distribution of local SRT near walls in the annulus and fountain. Moreover, the local SRTs in different regions of the system show distinct distribution properties.

Global characteristics of non-premixed jet flames of hydrogen–hydrocarbon blended fuels

Blending hydrogen into hydrocarbon fuels can reduce the carbon-intensity of the fuel and extend the lean flammability limit. However, limited information is available of the global performance of attached, non-piloted hydrogen–hydrocarbon jet flames under well-defined boundary conditions. Three groups of blended fuels were investigated in the current study: Natural gas +H2 (with H2 volume fraction varying from 18.6% to 100%), C2H4+H2 (with H2 volume fraction varying from 0% to 100%), and 40% C2H4+41% H2+19% N2. Measurements were performed of flame dimensions, radiant fraction, and emission indices of NOx and CO. For flames with constant exit strain rate, the increase of hydrogen volume fraction was found to decrease the radiant fraction, decrease the global residence time and increase the NOx emission index. For flames of the same fuel composition, a higher strain rate results in a lower radiant fraction. The NOx production rate scales with the reciprocal of non-adiabatic flame temperature, consistent with the thermal NOx mechanism. The CO/CO2 ratio is determined by the competing influences of flame residence time, carbon input rate and mixing rate of the fuel and air.

The CO/NOx Emissions of Swirled, Strongly Pulsed Jet Diffusion Flames

The CO and NOx exhaust emissions of swirled, strongly pulsed, turbulent jet diffusion flames were studied experimentally in a coflow swirl combustor. Measurements of emissions were performed on the combustor centerline using standard emission analyzers combined with an aspirated sampling probe located downstream of the visible flame tip. The highest levels of CO emissions are generally found for compact, isolated flame puffs, which is consistent with the quenching due to rapid dilution with excess air. The imposition of swirl generally results in a decrease in CO levels by up to a factor of 2.5, suggesting more rapid and compete fuel/air mixing by imposing swirl in the coflow stream. The levels of NO emissions for most cases are generally below the steady-flame value. The NO levels become comparable to the steady-flame value for sufficiently short jet-off times. The swirled coflow air can, in some cases, increase the NO emissions due to a longer combustion residence time due to the flow recirculation within the swirl-induced recirculation zone. Scaling relations, when taking into account the impact of air dilution over an injection cycle on the flame length, reveal a strong correlation between the CO emissions and the global residence time. However, the NO emissions do not successfully correlate with the global residence time. For some specific cases, a compact flame with a simultaneous decrease in both CO and NO emissions compared to the steady flames was observed.

Chemical fate, latitudinal distribution and long-range transport of cyclic volatile methylsiloxanes in the global environment: A modeling assessment

Cyclic volatile methylsiloxanes (cVMS) such as octamethycyclotetrasiloxane (D4), decamethycyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) are widely used as intermediates in the synthesis of high-molecular weight silicone polymers or as ingredients in the formulation of personal care products. The global environmental fate, latitudinal distribution, and long range transport of those cVMS were analyzed by two multimedia chemical fate models using the best available physicochemical properties as inputs and known persistent organic pollutants (POPs) and highly persistent volatile organic chemicals (“fliers”) as reference. The global transport and accumulation characteristics of cVMS differ from those of typical POPs in three significant ways. First, a large fraction of the released cVMS tends to become airborne and is removed from the global environment by degradation in air, whereas known POPs have a tendency to be distributed and persistent in all media. Secondly, although cVMS can travel a substantial distance in the atmosphere, they have little potential for deposition to surface media in remote regions. This contrasts with a deposition potential of known POPs that exceeds that of cVMS by 4–5 orders of magnitude. Thirdly, cVMS have short global residence times with the majority of the global mass removed within 3months of the end of release. Global residence times of POPs on the other hand are in years. The persistent fliers resemble the cVMS with respect to the first two attributes, but their global residence times are more like those of the POPs.

Influence of a combustion-driven oscillation on global mixing in the flame from a refinery flare

An assessment of the influence of strong combustion-driven oscillations on mixing rates and visible radiation in the flame from a full-scale refinery flare is reported. Importantly, the oscillations were generated naturally, with no external forcing, and at a high Reynolds number of 4 × 10 6. These conditions differentiate this study from those of previous investigations, which all involved some external forcing and were at a Re too low to ensure fully turbulent flow within the flame. A frame-by-frame analysis of video footage, providing good resolution of the instantaneous edge of each flame, was used to assess flame dimensions, and so to determine a global residence time. Since the flames are in the fast-chemistry regime, the visual imagers can be used to determine a global mixing rate. The analysis reveals a consistent picture that the combustion-driven oscillations do not result in a significant change to the global mixing rate, but do increase the visible radiation. This is in contrast to previous investigations, using externally forced jets, where forcing at the preferred mode has been found to increase mixing rates and reduce radiation.

CO/NOx Emissions of Strongly Pulsed Jet Diffusion Flames

The CO and NOX emissions of strongly pulsed, turbulent diffusion flames were examined experimentally in a co-flow combustor. Video imaging was performed and time-averaged emissions were measured at the combustor exit and near the visible flame tip. Both the case of a fixed fuel injection velocity during the injection interval and a constant fuelling rate were studied for jet Reynolds numbers ranging from 5,000 to 15,000. For fixed injection velocity, maximum emission indices of CO occurred for compact, isolated flame puffs. CO decreased substantially with decreasing jet-off time as the flame puff interaction increased. The pulsed flames had lower NOX than the steady flames, particularly for the case of isolated flame structures. Similar trends in NO formation were seen for constant fueling rate. The CO emissions were, however, considerably different, largely due to a significant impact of the Reynolds number. Radial emissions profiles suggest an improved fuel/air mixing for shorter jet-off times and longer jet-on times. The correlation of CO/NO emissions with a global flame residence time is discussed.

Cold flow studies of a slurry transport reactor–hydrocyclon system

The fluid dynamics of a new reaction system composed of a slurry transport reactor–hydrocyclon were studied using two column diameters at different gas and liquid linear velocities. The cold models used a gas collector in the top that allowed measurement of the gas disengaged by radial zones and a conductimetric probe that measured the frequency of the bubbles exiting from the top of the reactor. Gas and liquid hold-ups were determined. Liquid and solid tracers were also employed to determine the resident time distribution (RTD), global residence time, and the recycle of slurry near the wall. The results show the effect of sparger and disengaging design, as well as the effect of gas and liquid flow rate on the radial and axial gas hold-up profiles and on the recycle of slurry by the wall. This recycle is similar to those observed with a draft tube. No significant effect of column diameter was observed. A smooth circulation of slurry and solid was achieved through a mechanical optimization of the inlet and outlet of the reactor. It was demonstrated that the RTD of the system can be simulated using a set of continuous stirred tank reactors and plug flow reactor in a recycle (three parameters). Empirical equations are proposed for predicting the hold-up and the three parameters needed by the model. The similarity to a spouted bed reactor is discussed.

Scaling of NO x emissions from a laboratory-scale mild combustion furnace

A systematic experimental campaign has been carried out to investigate the scaling of NO x emissions from a moderate or intense low-oxygen dilution (MILD) combustion furnace operating with a parallel jet burner system in which the reactants and the exhaust ports are all mounted on the same wall. Its maximum capacity was 20 kW from the fuel and 3.3 kW from air preheat, with a turndown ratio of 1:3. The burner system was configured to achieve high dilution of the incoming reactants. A comprehensive data set comprising 191 global measurements of temperature and exhaust gas emissions is presented, together with temperature contours on the furnace centerline plane. It was found that, although heat extraction, air preheat, excess air, firing rate, dilution, and fuel type all affect global NO x emissions, they do not control NO x scaling. The combined effects of these global parameters can be ultimately characterized by a furnace temperature and a global residence time. A temperature–time scaling approach, previously reported for open jet diffusion flames, proved to be a useful tool for comparison of NO x emissions from highly diluted furnace environments regardless of the furnace/burner geometries. Regression-based predictions found the characteristic temperature to correlate with 85% of the data with an accuracy of only ±50%. The leading-order approach also showed that the jet exit Froude number is of limited value for NO x scaling in the MILD regime. Because of the weak dependence on temperature observed in the data and the moderate magnitude of the measured temperatures, it is deduced that the prompt-NO and/or N 2O-intermediate pathways are of significance comparable to that of the thermal-NO pathway. The analysis also suggests that NO x formation is controlled neither by kinetics nor by mixing, and hence the conditions inside this furnace approach or span the range in which Damköhler numbers are of order unity, Da = O ( 1 ) .

SOOTING BEHAVIOR DYNAMICS OF A NON-BUOYANT LAMINAR DIFFUSION FLAME

Local soot concentrations in non-buoyant laminar diffusion flames have been demonstrated to be the outcome of two competitive processes, soot formation and soot oxidation. It was first believed that soot formation was the controlling mechanism and thus soot volume fractions could be scaled with a global residence time. Later studies showed that this is not necessarily the case and the local ratio of the soot formation and oxidation residence times is the prime variable controlling the ultimate local soot volume fractions. This ratio is a strong function of geometry and flow field, thus a very difficult variable to properly quantify. This study presents a series of microgravity, low oxidizer flow velocity, experiments where soot volume fraction measurements have been conducted on a laminar, flat plate boundary layer type diffusion flame. The objective of the study is to determine if the above observations apply to this type of diffusion flames. The fuel is ethylene and is injected through a flat plate porous burner into an oxidizer flowing parallel to the burner surface. The oxidizer consists of different mixtures of oxygen and nitrogen, flowing at different velocities. These experiments have been complemented with numerical simulations that emphasize resolution of the flow field to simulate the trajectory of soot particles and to track their history from inception to oxidation. The results validate that local soot volume fractions are a function of the local formation and oxidation residence times and are not necessarily a function of the global residence time. For this particular geometry, an increase in oxidizer velocity leads to local acceleration that reduces the oxidation residence time, leading to higher soot concentrations. It was also observed that the flames become longer as the flow velocity is increased in contrast with the reversed trend observed in flames at higher flow velocities. This result is important because it seems to indicate the presence of a maximum in the flame length and luminosity below those encountered in natural convection. The result would have implications for fire safety in spacecrafts since the ambient gas velocities are below those observed in natural convection, and longer and more luminous flames represent a higher hazard.

Radiative fraction and optical thickness in large-scale hydrogen-jet fires

The radiative characteristics of large-scale (visible length 1.4–9.1 m) hydrogen jet flames that simulate an accidental leak from a high-pressure hydrogen container were compared with previous experimental and theoretical results for laboratory-scale non-sooting flames. The comparison shows that correlations of radiative heat fraction with global residence time need to account for the differences in thermal emittance of combustion gases for different fuels. This correction was found to be particularly important when hydrogen flames were compared to flames with CO 2 as a product specie. Measurements of the radiative heat fraction for CO/H 2, CH 4 and H 2 flames collapse onto one line when plotted against the logarithm of a characteristic residence time weighted by a factor that accounts for differences in the radiative characteristics of combustion gases. The radiative fraction of large-scale jet flames was found to be smaller than that predicted by the correlation obtained for laboratory-scale flames. This was explained by an increase in optical thickness as the flame size increases.

Interactions between soot and CH ∗ in a laminar boundary layer type diffusion flame in microgravity

A three-dimensional laminar non-buoyant diffusion flame was studied with the objective of improving the understanding of the soot production. The flame originated from a porous ethylene burner discharging into a laminar boundary layer. Soot volume fractions were measured using Laser-Induced Incandescence (LII), and the spontaneous emission from CH ∗ was determined using chemiluminescence. The main parameter varied was the oxidizer flow. CH ∗ measurements allowed the identification of the reaction zone, while LII measurements permitted the tracking of soot. It was observed that soot volume fractions are inversely proportional to the global residence time. This is in contradiction to previous studies on axi-symmetric non-buoyant diffusion flames. The combined measurements allowed it to be established that the apparently contradictory behaviour can be explained by an analysis of the influence of the flow field on the ratio of soot production to oxidation.

Does the Forest Filter Effect Prevent Semivolatile Organic Compounds from Reaching the Arctic?

Forests act as efficient filters for many airborne semivolatile organic compounds (SOCs). However, most simulations of an organic chemical's long-range transport in the atmosphere do not account for this filter effect. In this study, forests are introduced into an existing zonally averaged global distribution model (Globo-POP) to investigate how such a change affects a chemical's potential to undergo long range transport and accumulation in the Arctic, as quantified by the Arctic contamination potential (ACP). Simulation results indicate that the ACP of a "space" of perfectly persistent hypothetical organic chemicals, defined by log KOA and log KAW, is reduced by introducing forests in the global model. Depending on partition characteristics, this reduction can be as large as a factor of 2. Model calculations also indicate that it is mostly the boreal forests, specifically boreal deciduous forests, which play a key role in this respect. Sensitivity analyses establish the deposition velocity to boreal forests, especially for gaseous compounds, as one of the most influential parameters controlling this global forest filter effect. The extent of the effect is further sensitive to the forest density and precipitation rate in the boreal zone, and the degradation rates of the chemical. Specifically, degradation in the forest canopy may enhance the effect and further reduce an SOC's long range transport to remote regions. Simulations for three PCB congeners suggest that forests may reduce concentrations in air, ocean, and freshwater at the expense of increased concentrations in forest soils and may lead to substantially increased overall global residence times.

Reduction of PFC emissions to the environment through advances in CVD and etch processes

One the most focused environmental health and safety (EHS) goals for the semiconductor industry has been to reduce perfluorocompound (PFC) emissions because of their high global warming potentials and long residence times in the atmosphere. During the last decade, significant achievements have been reached in attaining this goal. Chemical vapor deposition (CVD) chamber cleaning and plasma etch are two processes that use PFCs in which studies have been conducted to reduce emissions. Two successful strategies for reducing PFC emissions and enhancing process performance are described.