|Year : 2011 | Volume
| Issue : 1 | Page : 5-10
Anesthetic gases and global warming: Potentials, prevention and future of anesthesia
Hina Gadani, Arun Vyas
Department of Anesthesiology, M.P. Shah Medical College, Jamnagar, Gujarat, India
|Date of Web Publication||23-Aug-2011|
501, Sumeru Residency, Opp. Manusmruti Apartment, Palace Road, Jamnagar, Gujarat - 361 008
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Global warming refers to an average increase in the earth's temperature, which in turn causes changes in climate. A warmer earth may lead to changes in rainfall patterns, a rise in sea level, and a wide range of impacts on plants, wildlife, and humans. Greenhouse gases make the earth warmer by trapping energy inside the atmosphere. Greenhouse gases are any gas that absorbs infrared radiation in the atmosphere and include: water vapor, carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), halogenated fluorocarbons (HCFCs), ozone (O 3 ), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs). Hazardous chemicals enter the air we breathe as a result of dozens of activities carried out during a typical day at a healthcare facility like processing lab samples, burning fossil fuels etc. We sometimes forget that anesthetic agents are also greenhouse gases (GHGs). Anesthetic agents used today are volatile halogenated ethers and the common carrier gas nitrous oxide known to be aggressive GHGs. With less than 5% of the total delivered halogenated anesthetic being metabolized by the patient, the vast majority of the anesthetic is routinely vented to the atmosphere through the operating room scavenging system. The global warming potential (GWP) of a halogenated anesthetic is up to 2,000 times greater than CO 2 . Global warming potentials are used to compare the strength of different GHGs to trap heat in the atmosphere relative to that of CO 2 . Here we discuss about the GWP of anesthetic gases, preventive measures to decrease the global warming effects of anesthetic gases and Xenon, a newer anesthetic gas for the future of anesthesia.
Keywords: Climate impact, global warming, inhaled anesthetic gases, Xenon
|How to cite this article:|
Gadani H, Vyas A. Anesthetic gases and global warming: Potentials, prevention and future of anesthesia. Anesth Essays Res 2011;5:5-10
|How to cite this URL:|
Gadani H, Vyas A. Anesthetic gases and global warming: Potentials, prevention and future of anesthesia. Anesth Essays Res [serial online] 2011 [cited 2021 May 6];5:5-10. Available from: https://www.aeronline.org/text.asp?2011/5/1/5/84171
| Introduction|| |
Greenhouse gases which include: water vapour, carbon dioxide, nitrous oxide, halogenated flurocarbons and hydroflurocarbons (HFCs)  absorbs the infrared radiation in the atmosphere and in turn makes the earth warmer. Over the last 100 years, the average air temperature near the earth's surface has risen by a little less than 1 degree Celsius or 1.3 degrees Fahrenheit. The data show that an increase of 1 degree Celsius makes the earth warmer now than it has been for at least a thousand years. The top 11 warmest years on record have all been in the last 13 years, said NASA in 2007, and the first half of 2010 has already gone down in history as the hottest ever recorded. The UN climate change body, the Intergovernmental Panel on Climate Change (IPCC) says that global surface temperature will probably rise a further 1.1 to 6.4 degrees Celsius (2.0 to 11.5 degrees Fahrenheit) during the 21 st century.  The GWP (Global Warming Potential) factor of a substance is calculated as the warming potential over e.g. 100 years for a kilogram of the substance in gaseous phase relative to a kilogram of carbon dioxide (CO 2 ).  Global warming potentials are used to compare the strength of different greenhouse gases (GHGs) to trap heat in the atmosphere relative to that of CO 2 .  Inhaled anesthetics are recognized GHGs. Calculating their relative impact during common clinical usage will allow comparison to each other and to CO 2 emissions in general.  While no one is suggesting that patients should not receive needed anesthetics because of the risk of climate change, some simple steps could help to limit their environmental impact.  Introduction of a new anesthetic agent-Xenon will be helpful to prevent global warming in the future.
| Anesthetic Gases|| |
Desflurane is halogenated ether. Together with sevoflurane it is gradually replacing isoflurane. It has the most rapid onset and offset of the volatile anesthetics due to its low solubility in blood. 
Isoflurane (1-chloro-2, 2, 2-trifluoroethyldifluoromethyl ether) is a halogenated ether. It is now being replaced with sevoflurane, desflurane and the intravenous anesthetic propofol. 
Nitrous oxide (N 2 O) is a colorless, non-flammable gas, with a pleasant slightly sweet odor. It is commonly known as laughing gas due to the exhilarating effects and is used in surgery and dentistry for its anesthetic and analgesic effects. 
Sevoflurane (2, 2, 2-trifluoro-1-(trifluoromethyl) ethyl ether), also called fluoromethyl, is a halogenated ether used for induction and maintenance of general anesthesia. Together with desflurane, it is replacing isoflurane and halothane in modern anesthesiology. After desflurane it is the volatile anesthetic with the fastest onset and offset. 
These inhalant anesthetics undergo very little metabolic change in the body - the gases exhaled by the patient are almost identical to those administered by the anesthetist. The anesthetics "usually are vented out of the building as medical waste gases". "Most of the organic anesthetic gases remain for a long time in the atmosphere where they have the potential to act as greenhouse gases."  The average composition of the waste gases is estimated to be: 
Nitrous oxide 5-10%
Volatile halocarbon 0.1-0.5%.
| Parts of Atmosphere|| |
The atmosphere is subdivided into various parts. The lowermost layer is the troposphere between 8 to 18 kilometers. Above this, up to 50 km is the stratosphere. The others are the mesosphere, thermosphere and exosphere. For us only the troposphere and stratosphere are important. They are referred as atmosphere in this article. 
Atmospheric/Tropospheric lifetimes of halogenated anesthetics
The atmospheric lifetimes of the halogenated anesthetics halothane, enflurane, isoflurane, desflurane and sevoflurane have been determined from observations of hydroxyl radical (OH) reaction kinetics and ultraviolet (UV) absorption spectra. Rate coefficients for the reaction with OH radicals for all halogenated anesthetics investigated ranged from 0.44 to 2.7×10 -14 cm 3 /molec/s. Halothane, enflurane and isoflurane showed distinct UV absorption in the range 200-350 nm. No absorption in this wavelength range was detected for desflurane or sevoflurane. The total atmospheric lifetimes, as derived from both OH reactivity and photolysis, were 4.0-21.4 years. It has been calculated that up to 20% of anesthetics enter the atmosphere. Comparison with a one-dimensional model indicates that the lifetimes of halothane, enflurane and isoflurane with respect to this reaction are two, six and five years, respectively. Thus the small production of the anesthetics is not offset by anomalously long atmospheric lifetimes to give a large atmospheric burden of the compounds. ,
Ozone depletion potential
As a result of chlorine and bromine content, the ozone depletion potential (ODP) relative to chlorofluorocarbon (CFC)-11 varies between 0 and 1.56, leading to a contribution to the total ozone depletion in the stratosphere of approximately 1% by halothane and 0.02% by enflurane and isoflurane. The stratospheric impact and their influence on ozone depletion is of increasing importance because of decreasing chlorofluorocarbons globally. ,,
| Climate Impact of the Anesthetic Gases|| |
Nitrous oxide-nothing to laugh about
It is a mainstay in anesthesia, having been used for over 150 years. Clinical sources of N 2 O form only 1% of the total human contribution of this gas to the atmosphere, which contributes less than 0.05% to the greenhouse effect. As a waste anesthetic it contributes roughly 0.1% of the whole global warming. In recent years, the climate impact from the use of N 2 O in healthcare has become topical. ,, When choosing an anesthetic, it is important to consider all aspects of environmental responsibility, not just global warming. Its long atmospheric lifetime of about 150 years and
its strong warming potential, more than 300 times stronger than CO 2 , makes it an effective agent of global warming.  It is involved in the destruction of the ozone layer. Contribution to human-induced climate change is 7%.
Isoflurane, sevoflurane and desflurane
Institute for vibrant living (IVL) has conducted a literature review to find information on the climate impact of anesthetic gases, which was also compared with the climate impact from energy use.
The only study concerning isoflurane and sevoflurane found in peer-reviewed literature was a German study from 1999. This study calculated GWP relative to CFC-12 rather than CO 2 .
GWP100 (hundred-year GWP) values for the inhaled anesthetics: 
Desflurane-1526, N 2 O-296, isoflurane-350, sevoflurane-575.
GWP 20 (Twenty-year GWP) values for the inhaled anesthetics: 
Sevoflurane-349, isoflurane-1401, desflurane-3714.
CDE 20 (carbon dioxide equivalent) values for 1 MAC-hour at 2 L fresh gas flow (N 2 O/O 2 ):sevoflurane-1, isoflurane-2.2, desflurane-26.8. 
When 60% N 2 O/40% oxygen replaced air/oxygen as a carrier gas combination, and inhaled anesthetic delivery was adjusted to deliver 1 MAC-hour, sevoflurane CDE 20 values were 5.9 times higher with N 2 O than when carried with air/O 2 , isoflurane values were 2.9 times higher, and desflurane values were 0.4 times lower. On a 100-year time horizon with 60% N 2 O, the sevoflurane CDE 100 values were 19 times higher than when carried in air/O 2 , isoflurane values were 9 times higher, and desflurane values were equal with and without N 2 O. 
In order to compare the climate change potential of the different anesthetic gases based on the current consumption volumes, the Lund University Hospital results shows that N 2 O stands for practically 100% of the climate change potential, although it has the lowest GWP factor out of the four anesthetic gases, the consumed volume of N 2 O far outweighing the volumes used of the other gases.  Climate impact of the use of anesthetic gases was compared with the climate impact of energy use. Lund University Hospital used 37 000 MWh of electricity and 50 332 MWh of district heating in 2006. Climate impact of the anesthetic gases corresponds to about one-third of the climate impact emanating from energy use. 
| Conclusions|| |
Although isoflurane,  sevoflurane and desflurane all have higher GWP factors than N 2 O, and the GWP factor of desflurane is five times higher than that of N 2 O, N 2 O is contributing the most to increased climate impact (99.97%) as the consumption volumes of N 2 O far exceed those of the other anesthetic gases.
Replacing N 2 O with the other anesthetic gases may be beneficial. The anesthetic effect can be achieved with lower use volumes than the corresponding effect of N 2 O. This was not studied.
The climate impact of anesthetic gases corresponds to about one-third of the climate impact of the use of electricity and district heating.
N 2 O is destructive to the ozone layer as well as possessing GWP, it continues to have impact over a longer timeframe, and may not be an environmentally sound tradeoff for desflurane. Avoiding N 2 O and unnecessarily high fresh gas flow rates can reduce the environmental impact of inhaled anesthetics. 
Desflurane has a much longer "lifetime" in the atmosphere than the other anesthetics studied, 10 years, compared to 1.2 years for sevoflurane and 3.6 years for isoflurane. Considering the flow rates at which the different anesthetics were given, desflurane had about 26 times the GWP of sevoflurane and 13 times the impact of isoflurane. 
Inhaled anesthetics are recognized greenhouse gases. They are "medically essential" and have been only cursorily investigated. 
Depending on the types of anesthetic used, an average midsize hospital has an environmental impact comparable to that of 100 to 1,200 cars per year. Using desflurane for one hour is equivalent to 235 to 470 miles of driving. 
| Prevention of Global Warming by Inhaled Anesthetics|| |
In the UK 100 ppm for each eight-hour work period, safety is assured with routine scavenging system. Produced by digesting bacteria, nitrous oxides are part of the nitrogen cycle, one of the most important chemical reactions on earth. Emissions from transportation, once a major source of nitrous oxide, have decreased recently due to the use of catalytic converters in modern cars. Reducing nitrous oxide emissions is also cheaper than reducing CO 2 or methane emissions, according to the US Environmental Protection Agency. 
Other inhaled anesthetics
Ontario hospital clean air challenge 
This encourages investigating how to remove the volatile halocarbons of waste anesthetic gases from surgical facilities before such gases are vented to the atmosphere.
- Use scavenging systems.
- Employ capture technology that uses canisters to collect anesthetics.
- Waste reduction.
- Improve segregation of non-hazardous waste from biomedical waste.
- Usage of single-use items.
- Use less disposables.
- More reprocessing of instruments within hospital.
To reduce hazardous chemical emissions levels:
Collect baseline data which contributes information to overall program reporting for environment and cost analysis.
- Introduce new ideas.
- Change engrained behavior and create the desire among staff, patients, suppliers and volunteers to attempt something different.
- Involve green team/environmental team, medical gas and equipment suppliers.
- Let people know about the success of new operation room gas reclamation project and the impact it is having on cost saved and environmental damage spared.
- Use protocol from colleagues, workshops, training seminars.
- Stress importance of the new initiatives (emissions reduced, cost saved, improved health [patient/staff and environmental] benefits, quantity of hazardous materials/chemicals reduced from workplace, etc.)
- Consider putting your message in their native language.
- A reward for reducing use or exposure to specific agents and chemicals for staff.
Blue-zone technologies 
A technology to capture, reclaim, and purify halogenated inhalation anesthetic gases used in hospital operating rooms. The technology could capture the vented gases and thereby extend the lifecycle of the anesthetic gases by 10 to 20 times. In future, this technology could enable hospitals to achieve significant savings in their expenditures on anesthetic gases as well as preventing harmful GHG emissions.
Hospitals for a healthy environment (H2E) 
A national movement for environmental sustainability in healthcare. H2E is educating healthcare professionals about pollution prevention opportunities and providing a wealth of practical tools and resources to facilitate the industry's movement toward environmental sustainability.
A simple scavenging system outside the operating room leads to 97.3% reduction of the mean concentration of halothane in the operation room atmosphere and reduction of 72% end-tidal samples of anesthetics with Magill semi-closed circuits. The scavenging systems can pose a serious risk to patients because of faulty or inappropriate equipments and inadequate checking.
"Inhaled anesthetics are 'greenhouse gases' that facilitate the trapping of solar energy and contribute to global warming," comments Dr. Steven L. Shafer of Columbia University, Editor-in-Chief of Anesthesia and Analgesia. "This study calculates how much inhaled anesthetics contribute to greenhouse gas emissions, and offers specific suggestions about how anesthesiologists can reduce the impact of anesthesia care on global warming."
| Xenon - A Modern Anesthetic|| |
Xenon (XE) is well known as an inert gas.  Although named after a Greek word for 'stranger', Xenon is becoming less of a stranger for anesthesiologists. Lawrence published initial experiments with xenon anesthesia in 1946. Xenon belongs to the group of noble gases and is found in very small concentration in the air (0.0000087%). It is manufactured by fractional distillation of liquefied air, which is obtained as a byproduct during the process of pure oxygen production. After several separation processes, a purity of 99.995% can be obtained, only impurity being O 2 and N 2 . The production of one liter of xenon consumes 220-Watt hours of energy. The current world production of xenon is approximately 10 million liters per year. Only 1.5 million liters per year is utilized for medical purposes, with half of this amount being used for anesthetic purposes. The cost of Xe is extremely high (approx USD 10.00 per liter).
Mechanism of action
Xenon has many properties of an ideal anesthetic gas.  These include:
- Xenon inhibits plasma membrane Ca++ pump, which may be responsible for an increase in neuronal Ca++ concentration and altered excitability.
- It acts selectively by blocking the N-methyl-d-aspartate (NMDA) receptor. This NMDA receptor inhibitor is responsible for inhibition of the nociceptive responsiveness of the spinal dorsal horn neurons. Xe inhibits the function of the NMDA subtype of the glutamate receptor and nicotinic acetylcholine receptor. How it does so remains a mystery. Being inert, it displays an extremely low chemical reactivity, therefore it alters the function of these receptors via physiochemical means.
- It hardly affects the function of the gamma-amino butyric acid receptor but produces hypnotic effect electrophysiologically.
Xenon and the global environment
- Non-inflammable and non-explosive.
- Rapid induction and emergence due to its low blood gas partition coefficient (0.12), which is the lowest of all known anesthetics.
- Minimum alveolar concentration (MAC) value of 0.63 makes it suitable as sufficient analgesic and hypnotic effect in a mixture of 30% O 2 . It is 1.5 times more potent than N 2 O.
- The absence of metabolism, low toxicity and devoid of teratogenicity.
- Xenon anesthesia produces highest regional blood flow in the brain, liver, kidney and intestine. Dangers of tissue hypoxia are greatly reduced. It therefore appears to be an interesting alternative for anesthesia in transplant surgery.
- It may protect neural cells against ischemic injury. During cardiopulmonary surgery its neuroprotective effect is confirmed.
- Despite higher density than N 2 O it does not alter respiratory mechanics. Airway resistance is not increased and diffusion hypoxia is less than N 2 O.
- Xenon does not alter voltage-gated ion channels in the myocardium, nor does it sensitize the myocardium to the dysrhythmogenic effects of epinephrine. Lack of cardiovascular depression is the most appealing characteristic of Xenon. Even with 80% concentration of Xe, Ca++  flow in human cardiomyocytes remains unaffected.
- The unique combination of analgesia, hypnosis and lack of hemodynamic depression  makes it a very attractive choice for patients.
Xe being a part of atmosphere and manufactured from liquefied air, does not add to atmospheric pollution when emitted from the anesthetic circuit because it simply goes back to the atmosphere. It does not contribute to the depletion of the ozone layer and global warming.
Future of anesthesia
- Because of its rarity and expensiveness, the use of this gas as an anesthetic agent can be justified only if its waste is reduced to absolute minimum. It must be applied via rebreathing system using the lowest possible gas flow. 
- An electronically controlled anesthesia delivery system that continuously monitors gas concentration inside the breathing circuit may be used for this purpose. A closed loop feedback control mechanism delivers Xe and oxygen into the system in the amount needed to maintain constant gas concentration and circulating gas volume.
- Recycling of Xe contained in the gas escaping via the exhaust port rather than wasting it into the atmosphere is the only way to guarantee the availability of a sufficient amount of Xe for routine use as an anesthetic gas.
- The environment friendliness of Xe strongly appeals to the increasing numbers of ecologically minded people in the anesthesia community.
- Mankind may not be able to live through the 21 st century if global warming and other forms of atmospheric pollution continue at the present rate.
It is hoped that the above information will encourage critical thinking about the venting of anesthetic agents that contribute to GHG emissions and environmental pollution and help invoke changes within your organization's operating room practices.
| References|| |
|1.||Massachusetts EPP Glossary of terms. Available from: http://www.mass.gov/Eoaf/docs/osd/epp/massepp_glossary.doc. [Last accessed on 2010 Oct 15]. |
|2.||Effects of climate change today. Available from: http://www.windows2universe.org/earth/climate/cli_effects.html. [Last accessed on 2010 Oct 15]. |
|3.||Ulrik Axelsson. Climate impact of the anaesthetic gases. Region Skåne. IVL Swedish Environmental Research Institute. Available from: http://www.miljo.skane.se/eng/U2237_translation.pdf. [Last accessed on 2010 Oct 15]. |
|4.||Ontario Hospital Clean Air Challenge : Hospitals healing the environment - Operating room gases. Available from: http://www.c2p2online.com/documents/BackgroundCALL9_OR_Gas_071907-CW.pdf. [Last accessed on 2010 Oct 15]. |
|5.||Brown AC, Canosa-Mas CE, Parr AD, Pierce JM, Wayne RP. Tropospheric lifetimes of halogenated anaesthetics. Nature 1989;341:635-7. Available from: http://bja.oxfordjournals.org/cgi/content/abstract/82/1/66. |
|6.||Study Shows Global Warming Impact of Anaesthetics. Available from: http://www.anesthesia-analgesia.org. [Last accessed on 2010 Oct 15]. |
|7.||Reference answers. Available from: http://www.answers.com/desflurane. [Last accessed on 2010 Oct 15] |
|8.||Reference answers. Available from: http://www.answers.com/isoflurane. [Last accessed on 2010 Oct 15]. |
|9.||Reference answers. Available from: http://www.answers.com/nitrous-oxide. [Last accessed on 2010 Oct 15]. |
|10.||Reference answers. Available from: http://www.answers.com/sevoflurane. [Last accessed on 2010 Oct 15]. |
|11.||System for removal of halocarbon gas from waste anesthetic gases. Available from: http://www.patentstorm.us/patents/6729329/description.html. [Last accessed on 2010 Oct 15]. |
|12.||Langbein T, Sonntag H, Trapp D, Hoffmann A, Malms W, Röth EP, et al. Volatile anaesthetics and the atmosphere: Atmospheric lifetimes and atmospheric effects of halothane, enflurane, isoflurane, desflurane and sevoflurane. Br J Anaesth 1999;82:66-73. Available from: http://bja.oxfordjournals.org/cgi/content/abstract/82/1/66 [Last accessed on 2010 Oct 15]. |
|13.||Clerbaux CD, Cunnold J, Anderson A, Engel P, Fraser P, Mahieu E, et al. Long- Lived Compounds, Chapter 1. In: Scientific Assessment of Ozone Depletion 2006, Global Ozone Research and Monitoring Project - Report No. 50. WMO, Geneva 2007. p. 1.1-1.63. |
|14.||Daniel J, Velders G, Douglas A, Forster P, Hauglustaine D, Isaksen I, et al. Halocarbon Scenarios, Ozone Depletion Potentials, and Global Warming Potentials, Chapter 8. In: Scientific Assessment of Ozone Depletion 2006. |
|15.||Ryan SM, Nielsen CJ. Global Warming Potential of Inhaled Anesthetics: Application to Clinical Use. Available from: http://www.anesthesia-analgesia.org/content/111/1.toc. [Last accessed on 2010 Oct 15]. |
Ravishankara AR, Daniel JS, Portmann RW. Nitrous oxide (N2O): The dominant ozone-depleting substance emitted in the 21st century. Science 2009;326:123-5. |
|17.||In and out of the world we live in. Available from: http://knowledge.allianz.com/en/globalissues/climate_change/global_warming_basics/nitrous_oxide_greenhouse_gas_profile.html. [Last accessed on 2010 Oct 15]. |
|18.||Byrick B. Reclamation of Exhaled Vapour Anesthetic: Evaluation of a New Technology. The Canadian Journal of Anesthesia. Available from: http://www.bluezone.ca/docs/Reclamation.pdf. [Last accessed on 2010 Oct 15]. |
|19.||Hospitals for a Healthy Environment (H2E) Available from: http://www.h2eonline.org/. [Last accessed on 2010 Oct 15]. |
|20.||Farquhar-Thomson DR, Goddard JM. The hazards of anaesthetic gas scavenging systems. Anaesthesia 1996;51:860-2. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2044.1996.tb12618.x/abstract;jsessionid=98876F 28BE915E0621753418E03371BE.d02t01 |
|21.||Mehta S, Cole WJ, Chari J, Lewin K. Operating Room Air Pollution: Influence of Anaesthetic Circuit, Vapour Concentration, Gas Flow and Ventilation. Can Anaesth Soc J 1975;22:265-74. |
|22.||Lara Hapley, Jo van Schalkwyk. Xenon - Recent developments. Available from: http://www.anaesthetist.com/anaes/drugs/Findex.htm#xenon.htm. [Last accessed on 2010 Oct 15]. |
|23.||Hanss R, Bein B, Turowski P, Cavus E, Bauer M, Andretzke M, et al. The influence of xenon on regulation of the autonomic nervous system in patients at high risk of perioperative cardiac complications. Br J Anaesth 2006;96:427-36. |
|24.||Bein B, Höcker J, Scholz J. Xenon--the ideal anaesthetic agent? Anasthesiol Intensivmed Notfallmed Schmerzther 2007;42:784-91. |
|25.||Leclerc J, Nieuviarts R, Tavernier B, Vallet B, Scherpereel P. Xenon anesthesia: From myth to reality. Ann Fr Anesth Reanim 2001;20:70-6. |
|This article has been cited by|
||Analytical Determination of Medical Gases Consumption and Their Impact on Hospital Sustainability
| ||Miguel Gómez-Chaparro,Justo García-Sanz-Calcedo,Luis Armenta Márquez |
| ||Sustainability. 2018; 10(8): 2948 |
|[Pubmed] | [DOI]|
||Greening the operating room
| ||Camila R. Guetter,Barbara J. Williams,Eliza Slama,Amanda Arrington,Marion C. Henry,Mecker G. Möller,Janet Elizabeth,Sharon Stein,Marie Crandall |
| ||The American Journal of Surgery. 2018; |
|[Pubmed] | [DOI]|
| ||Stefania Scarabelli,Carl Bradbrook |
| ||Companion Animal. 2017; 22(3): 134 |
|[Pubmed] | [DOI]|
||Adsorbent comparisons for anesthetic gas capture in hospital air emissions
| ||Mina Mehrata,Carol Moralejo,William A. Anderson |
| ||Journal of Environmental Science and Health, Part A. 2016; : 1 |
|[Pubmed] | [DOI]|