QUEBEC CITY -- Quebec Premier Francois Legault fired back at opposition parties Thursday, saying they “don’t respect public health,” following criticisms on air purification in schools.

One opposition critic fired back later in the day, saying the province's stance on air purifiers is all about saving money, and that it's ignored plenty of public health recommendations itself.

During a Thursday morning press conference, Legault was asked if parents and teachers should trust the judgment of Education Minister Francois Roberge after opposition leader Dominique Anglade recently called for his resignation over air quality testing in schools.

“Absolutely,” responded the premier. “There seems to be an obsession with installing air purifiers in every class... Public health has been clear from the start; air purifiers are not necessary."

According to Legault, public health authorities believe that "opening a window will do the job," he said.

"But the opposition, they don't respect public health. They don't believe what public health is saying."

Education Minister Jean-Francois Roberge said there is no evidence that poor air quality has contributed to any outbreaks of COVID-19 in schools.

He commented Thursday on revelations that there were several irregularities in sampling.

According to a Radio-Canada investigation, in three out of five tests, the protocol used tended to improve the results by reducing the amount of carbon dioxide in the classroom.

At a press conference Thursday morning in Parliament, Roberge acknowledged that the tests were not perfect.

However, he said he wanted to assure the public that the methodology was put in place by experts.

He said he has no evidence to suggest that poor air quality has contributed to outbreaks in classrooms.

In its January recommendations, the Ministry of Education did not mandate the installation of air purifiers in the province's schools.

Instead, it recommended that classroom windows be opened regularly to ventilate the space.

Then, in April, Radio-Canada reported that the system was actually left unclear -- the education ministry had not received an explicit signoff from public health on how it would test the air quality in schools in order to make COVID-19 related recommendations.

"I think the minister has really just signed his letter of resignation and has to step down, full stop," said Anglade at the time.

According to the province, however, there was a degree of collaboration between the ministries.

Shortly after, Quebec Public Health Director Dr. Horacio Arruda said "with regard to the issue of air quality in schools, we have also collaborated with the [education ministry], according to our expertise, on an ongoing basis."

LIBERALS SAY EXPLANATIONS STILL LACKING

On Thursday, after Legault's comments, Liberal education critic Marwah Rizqy said her party stands by its request for Roberge to resign and she rejected the idea they "don't respect" public health.

The government didn't follow several public health recommendations on schools or make them public for several months, Rizqy said, naming a few, including a recommendation last fall to cut down class sizes to allow more spacing.

Installing air purifiers also made sense, she said, and there's been little accountability on why it didn't happen.

"We all know that... to open a window, it's a good idea, of course it's a good idea," she said.

"But we're talking about the months of December, January and February," she said. When the Liberals pushed for purifiers "back in October, it's because we knew it would be too hard... in the middle of the winter in Quebec, it's not a good answer."

She also accused Roberge of being fundamentally motivated by saving money, and of refusing to say where federal COVID aid for schools went -- an issue raised in March.

"We have a government who don't want to spend the money for air purifiers, despite the fact that the fed government gave $432 million to open schools safely in Quebec," she said.

Roberge said "that the money was well spent," she said, and when asked for details, he wouldn't provide them.

"I can tell you it never went for air purifiers," Rizqy said.

SHIFTING GUIDELINES: SITUATION IN QUEBEC IS ‘MORE COMPLEX’

The premier also faced questions on rapidly shifting pandemic measures, including the recent shift towards mandatory outdoor masks when social distancing is impossible.

“If you’re not sure, wear a mask,” said Legault.

Rapidly changing health measures have frustrated some in recent days, but Legault asked Quebecers to remain patient.

Quebec has opted for a more regional approach than its neighbouring province Ontario, which recently ordered a province-wide shutdown, dubbed by lawmakers an “emergency break,” as cases reach new highs.

In Quebec, “it’s more complex,” said the premier.

“Here, we have a curfew, there, a school is closed, here, we have shops,” he said. “I think that’s more appropriate.”

- with files from The Canadian Press and CTV's Selena Ross