Plans to introduce more fresh air into Auckland's bus fleet to reduce the risk of Covid-19 transmission were abandoned due to cost.
RNZ's 'Whose Breath Are You Breathing?' project revealed carbon dioxide levels inside crowded buses could be in excess of 5000 parts per million, a number which has shocked scientists. It's more than six times the recommended safe indoor level to reduce the risk of Covid-19 transmission, which is 800ppm.
High readings can indicate how much exhaled air is in a space. At the highest reading on the buses, the equivalent of one in every seven breaths was made up of air breathed out by others.
Most Auckland buses also do not have windows which passengers are able to open, and air is not drawn from outside but instead recirculated inside the bus. However, Auckland's buses are not fitted with HEPA (high efficiency particulate air) air filtration, which filters virus particles.
Mask use is mandatory on public transport, but not policed.
Auckland Transport acting group manager of metro services Darek Koper said plans to improve air quality on buses were dropped due to cost.
"Based on the financial assessment of costs for the identified air treatment options and the efficacy and safety of the systems, it was decided to abandon the plans to introduce air purifications systems or introduce more fresh air onto existing buses and trains."
He said the investment required to change the public's perception of safety "without the scientific evidence and subject matter expert support" presented a challenge in justifying such investment.
Air inside buses is recirculated "to avoid introducing polluted air into the cabin from the urban environment".
Waka Kotahi's rules for urban buses, which include detailed rules for floor coverings, aisle width, handrail height and interior light, don't specify indoor air quality standards other than temperature.
Koper said Auckland Transport follows Ministry of Health advice and promotes high vaccination rates, mask use, and good hygiene onboard.
However, one Auckland bus driver who spoke to RNZ on the condition of anonymity said about 10 percent of passengers don't wear masks. He said drivers are not allowed to refuse entry to non-mask wearers and are told not to confront them, although he has in the past.
"I need to look after my health, and the other passengers."
Pleas for drivers to be supplied N95 masks were knocked back by the company, he said. Drivers were told the blue surgical masks were sufficient.
The CO2 measurements RNZ took over 17 bus trips showed readings between 871 and 5737ppm. Crowded buses had higher readings but even the lowest readings, taken on buses with fewer than 10 people aboard, exceeded levels considered safe.
University of Auckland aerosol chemist Dr Joel Rindelaub said CO2 readings of over 5000ppm were "absurdly high" and would indicate a high risk for Covid-19 transmission.
His advice to people using buses was to wear the best quality mask possible, such as an N95.
He was surprised at Koper's comment regarding scientific evidence.
"We do know that bringing in fresh air, especially in a place like public transit, could go a long way to help reduce the spread of Covid."
University of Michigan associate professor of engineering Jesse Capecelatro said Covid-19 risk on buses had been known about since the early days of the pandemic. One of the first documented super-spreading events occurred on a bus in China.
His research on buses found that air a person breathes out is breathed in by others within 50 seconds.
"Within 15 minutes with one person infected on the bus, no one wearing masks, about 50 percent of the bus was exposed above a so-called critical number of infectious particles that should give rise to infection."
If buses don't have windows which can be opened, he said passengers can reduce their risk by limiting the time spent on buses to fewer than 15 minutes, although he conceded this was impossible for many people.
Risk was further lowered by all passengers wearing well-fitted N95 masks, which reduced virus particles entering the bus air and into your airways.
"It also reduces the momentum" he said. "So if you were to cough, there's essentially a turbulent plume, a turbulent jet, leaving your mouth propelling these potentially infectious particles. When you wear a mask, it reduces that momentum so it won't spread as far and as fast."
He said it was disheartening to hear Auckland Transport was refusing to provide bus drivers with N95 masks.
"The bus driver is the most susceptible person on the bus. The longer you're on the bus, the more likely you are to breathe in a large number of infectious particles."
RNZ measured CO2 levels in Auckland buses and contacted Wellington and Canterbury regional councils to enquire if their buses used HEPA filters. A Wellington council spokesperson said these were not in use on Wellington's buses. Christchurch's buses had filters which removed dust particles. A question attempting to clarify whether these were HEPA filters went unanswered.