Editing Infrared (section)

=== Cooling ===

{{Main|Passive daytime radiative cooling}}

A variety of technologies or proposed technologies take advantage of infrared emissions to cool buildings or other systems. The LWIR (8–15&nbsp;μm) region is especially useful since some radiation at these wavelengths can escape into space through the atmosphere's [[infrared window]]. This is how [[passive daytime radiative cooling]] (PDRC) surfaces are able to achieve sub-ambient cooling temperatures under direct solar intensity, enhancing terrestrial [[heat flow]] to outer space with zero [[Efficient energy use|energy consumption]] or [[pollution]].<ref>{{Cite journal |last=Chen |first=Meijie |last2=Pang |first2=Dan |last3=Chen |first3=Xingyu |last4=Yan |first4=Hongjie |last5=Yang |first5=Yuan |year=2022 |title=Passive daytime radiative cooling: Fundamentals, material designs, and applications |journal=EcoMat |volume=4 |issue=1 |doi=10.1002/eom2.12153 |s2cid=240331557 |quote=Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. |doi-access=free}}</ref><ref>{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |bibcode=2019Joule...3.2057M |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |quote=By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth. |doi-access=free}}</ref> PDRC surfaces maximize shortwave [[solar reflectance]] to lessen heat gain while maintaining strong longwave infrared (LWIR) [[thermal radiation]] [[heat transfer]].<ref>{{Cite journal |last=Wang |first=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmc=7809060 |pmid=33446648 |quote=Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.}}</ref><ref>{{Cite journal |last=Zevenhovena |first=Ron |last2=Fält |first2=Martin |date=June 2018 |title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach |url=https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |journal=Energy |volume=152 |page=27 |bibcode=2018Ene...152...27Z |doi=10.1016/j.energy.2018.03.084 |access-date=2022-10-13 |via=Elsevier Science Direct}}</ref> When imagined on a worldwide scale, this cooling method has been proposed as a way to slow and even reverse [[global warming]], with some estimates proposing a global surface area coverage of 1-2% to balance global heat fluxes.<ref>{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |bibcode=2019Joule...3.2057M |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |quote=If only 1%–2% of the Earth's surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease. |doi-access=free}}</ref><ref>{{Cite journal |last=Zevenhovena |first=Ron |last2=Fält |first2=Martin |date=June 2018 |title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach |url=https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |url-status=live |journal=Energy |volume=152 |pages=27–33 |bibcode=2018Ene...152...27Z |doi=10.1016/j.energy.2018.03.084 |archive-url=https://web.archive.org/web/20241003190747/https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |archive-date=2024-10-03 |access-date=2022-10-13 |quote=With 100 W/m2 as a demonstrated passive cooling effect, a surface coverage of 0.3% would then be needed, or 1% of Earth's land mass surface. If half of it would be installed in urban, built areas which cover roughly 3% of the Earth's land mass, a 17% coverage would be needed there, with the remainder being installed in rural areas. |via=Elsevier Science Direct}}</ref>