UV Disinfection in Public Transportation (Part 1)
Cost-efficient, personal safety, reduced pollution, fewer accidents, and less traffic congestion are the typical benefits of public transport leading people to use transits. It is crucial to have a comfortable, reliable, and affordable public transportation system. One of the things passengers care deeply about is cleanliness especially with the spread of coronavirus these days. Disinfection and sterilization are essential for ensuring that transit vehicles do not transmit infectious pathogens to passengers. Growing concerns over possible cross infections via airborne micro-organisms, floors, cloth seats, most commonly touched - buttons, handrails, handles, ticket validators, and ticket vending machines induced people around the world to introduce UV1 disinfection. The germ-killing power of ultraviolet light can protect people from harmful germs resisting traditional forms of disinfecting. UV light provides rapid, effective inactivation of microorganisms through a physical process. It has been employed in the disinfection of transit vehicles and facilities. Disinfection procedures should be designed to remove all infectious pathogens. The paper addresses UV disinfection mostly in Moscow Metro Public Transport Systems . Russia is not the only place to use UV light. Due to the widespread outbreak of the coronavirus (COVID-19), New York MTA2 worked with Columbia University to test UV technology on its transits as shown in Figure 1 [2, 3]. TriMet3, NCTD4, and GCRTA5 have recently begun testing UV lights for interior surface disinfection . UV disinfecting has also being tested in India and Spain to disinfect transit vehicles and facilities to fight COVID-19 spread .
Figure 2. New York MTA UV disinfecting technology .
Metro Public Transport Systems
Much of the current debate revolves around whether it is wise to use the metro in corona time. It is a very controversial question rendering discussions. The UV disinfection asserts that it can be safe. Since the metro is an underground railway system, it is necessary to disinfect the air in addition to surfaces. A salient example would be the heavily populated Moscow Metro. The adequate UV doses to inactivate micro-organisms and pathogens were determined for three areas by LIT Technologies and the Russian Research Institute of Railway Hygiene: internal surfaces of train carriages, escalator handrails, the air in passageways and platforms in railway stations. Low-pressure mercury UV lamps have low energy efficiency so LIT Technology developed a series of straight and U-shaped LPHO6 “Amalgam” UV lamps for Metro disinfection applications . Amalgam lamps offer significantly greater power than low-pressure mercury UV lamps. Mercury low-pressure lamps typically have an electrical power of 0.3 to 0.5 W/cm2 of illuminated length but Amalgam lamps approach 6 W/cm2. Figure 2 shows 254 nm spectrum of a UV amalgam lamp and an effective spectrum for killing bacteria .
Figure 3. UV amalgam lamp for cell deactivation .
The optimum UVGI7 efficiency wavelength is about 254 nm. Aromatic amino acids are the main agents causing UV absorption between 220 and 280 nm simply because micro-organisms on surfaces are always embedded in and shielded by protective layers of proteins. Furthermore, the type and structure of surfaces like imitation-leather seats, linoleum, rubber escalator handrails, as well as glass and metal surfaces have a strong influence in dropping the overall UVGI efficiency, mainly because of the different structures create shadows for the UV radiation. The various UV doses at 253.7 nm to disinfect 90% for different types of surfaces can be seen in Figure 3.
Figure 4. UV doses at 253.7 nm for different surfaces .
Internal surfaces of train carriages
Internal surfaces and the air of train carriages was disinfected by a trolley equipped with two 170 W U-shaped amalgam lamps and a timer (Figure 4). The effect of different UV doses and irradiation cycle of the carriage has been shown in Table 1. Also the average percentage of disinfection left end, middle and right end of the seats and backs can be seen 
Figure 5. UV system for interior disinfection .
Table 1. The effect of UV irradiation on disinfection.
At present internal surfaces of train carriages and train interiors are exposed to 25 minute doses of UV-C.
UV radiation not only doesn’t add toxic substances but also reduces harmful chemicals. Chemical analysis results of air in metro carriages prior to and after 25 minute UV irradiation is shown in Table 2 .
Table 2. Chemical analysis results .
Escalator hand rails
Under UV system with two LIT U-shaped amalgam 170 W lamps about 10 seconds will be achieved 99 % disinfection escalator handrails (Figure 5) .
Figure 6. UV system on escalator handrails .
Air in passage ways and platforms in railway stations
UV disinfection air re-circulators of type AR-UF-170P-2 (with two 170 W lamps inside) with a capacity of
400 m3 /h disinfect with people inside the facility, for a continuously operation (Figure 6) .
Figure 7. UV disinfection air re-circulators .
 Kostyuchenko S, Khan A, Volkov S, Giller H. UV Disinfection in Moscow Metro Public Transport Systems. IUVA News, Moscow. 2009.
 Metro Magazine/ MET Staff; MTA to use UV light to clean transit system; https://www.metro-magazine.com/10112763/mta-to-use-uv-light-to-clean-transit-system.
 The Verge/ Andrew J. Hawkins; Here’s how NYC is using powerful UV light to kill the coronavirus on subways and buses; https://www.theverge. com/2020/5/20/21265221/nyc-mta-ultraviolet-light-uvc-coronavirus-disinfect-puro-pictures.
 Force RT. Cleaning and Disinfecting Transit Vehicles and Facilities During a Contagious Virus Pandemic.
 LEDinside - LED Industry Research/ YiningChen; Delhi Metro in India Adopt UV Light Disinfection to Enhance Safety after Reopen; http://www.ledinside.com/ news/2020/9/delhi_metro _uv_disinfection.
 Metro Report Interantional; Metro de Barcelona tests UV light disinfectant; https://www.railwaygazette.com/technology-data-and-business/metro-de-barcelona-tests-uv-light-disinfectant/56750.article.
 Heraeus Noblelight. UV IN AQUATICS: WELLNESS FOR THE NOSE -BREAKDOWN OF CHLORAMINES IN PUBLIC BATHS. IUVA News, Germany. 2009.