Fighter jets cut through crisp blue skies in Beijing last week for Chinese President Xi Jinping's Victory Day Parade.
The military hardware wasn't a rare sight but the colour of the sky was.
Normally heavy, toxic smog fills the air.
For all its military might, the political parade was a powerful symbol.
It meant the government's pollution control measures worked.
President Xi closed thousands of factories and halved traffic.
Although restrictions were temporary, things have been changing in Beijing.
Leves of harmful PM2.5 particles have dropped by a fifth, and the number of heavily polluted days have halved in the last five months.
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Greenpeace Climate and Energy Campaigner Liansai Dong said this was for two reasons.
"China is implementing new emission standards and new environment laws to push the improvements of air quality,” he said. “The second reason is that we are seeing a greater decrease in the coal consumption in the first half of this year versus last year.”
At the British School of Beijing, just outside of the city centre, they're noticing changes too.
Principal Andy Puttock said everyone was happy about air-quality improvements.
"I've been here three years and during that time our number of terrible days has got less and our number of lovely blue sky days like today has got more,” he said.
But a good air day in Beijing is still risky.
Mr Puttock said the school spent about $700,000 building a "dome" 18 months for students to play sport in.
"You need to maintain it, you need to keep it cool in summer and you need to keep it warm in winter. It's basically a big bubble,” he said. “It's blown up, inflated by air throughout the year with sealed doors to make sure that the air quality remains pretty much constant inside it.”
Teacher Joanne North said it had made a huge difference to the lives of students, teachers and parents.
"I can't imagine life without the dome,” she said.
Elsewhere in the school, air locks are routine and air purifiers a part of life.
The 'dome'. (SBS)
Coloured flags determine air quality. Green is for good, amber when children are allowed outside but for limited activity, and red when they can't go out at all.
Mr Puttock said last year there were 30 red days.
"What we're also interested in looking at is the amber days, the orange days when we do allow children outside but we limit the amount of activity they can do outside, and that will be about double that amount," he said.
However while Beijing's air quality may be improving, the overall situation in China wasn't looking good.
Ninety per cent of the cities Greenpeace ranked were exceeding the country's own yearly averages.
Greenpeace's Liansai Dong said the best solution was clean, renewable energy sources.
"Even though we are seeing improvements and a great decrease in the PM 2.5 concentration, by comparing with the WHO standard this is still much higher than the WHO standard which is 10 milligrams per cubic metre," she said.
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