I ONCE did a dangerous thing: I ran outdoors in Beijing. Actually not once but several times a week.
It's not that I'm a serious runner, but I needed to jog off fears that I was becoming - horrors - fat.
And so I would tighten my shoe laces, stretch my calves and pound the pavement as pram- pushing nannies and senior citizens looked on bemusedly.
I usually ran for about 40 minutes around my neighbourhood, past hardware shops, florists, restaurants selling buns, lamb skewers and the occasional sex shop.
Soon, I was out of breath but put it down to my lack of fitness.
But looking at the deadly air that has descended on Beijing in recent days, I ask myself why I used to exercise so recklessly.
Yesterday, I went to a park where I used to run to take photos for this story. I was there for 30 minutes - enough time to give me a headache and a scratchy throat.
Now I wonder what my badly exposed lungs would say to me if they could speak. Or maybe they won't speak to me. They would be too angry with me for exposing them to danger.
My lungs have every right to be upset. I used to also cycle 2km to work, wearing a helmet most times but never a face mask.
I didn't realise the irony until I covered the release of a study by Greenpeace East Asia and Peking University last month. The study found that air pollution was deadlier than road accidents!
The study zoomed in on PM2.5 pollution, referring to tiny particulates with a diameter of less than 2.5 micrometres, which are easily absorbed into the body.
Over the weekend, the capital's PM2.5 reading went off the charts, as the official measure goes up to only 500. The air smelt like something was burning when I went out on Saturday night.
The American Embassy's air monitor, however, showed density readings of more than 700 on Saturday, prompting many residents to declare that they were shutting their windows and battening down the hatches.
This is a grim matter, though some prefer to look on the bright side. A literature student who was visiting remarked that all the fog and mist made the lakes in the city's Houhai area look dreamy and poetic.
Others prefer to turn the smog particles into grist for humour.
The greatest distance on Earth is to stand on Tiananmen Square and not see Chairman Mao, wrote a netizen on the country's popular Sina microblog. A huge photo of the late Mao Zedong usually watches over the square, from its resting position at the entrance to the Forbidden City.
A dark Beijing tale most of us sojourners here would have heard of is the one about the non-smoker who lived here for too long and went home to find that her lungs had turned black.
To be fair, things have actually improved a little, not just according to official sources but also Beijing residents who say the air was a lot grimier before many polluting factories were moved because of the 2008 Olympics.
The capital's air has become cleaner for 14 years running, with the density of the bigger PM10 particles falling, the municipal environmental protection bureau said last month. "We can only improve air quality by making sure that pollution reduction outpaces increases in pollutants," said bureau spokesman Fang Li.
Now, that's tricky.
The worse the air gets, the more likely people like me will hop into a car or taxi instead of cycle or walk.
It doesn't help that Beijing's bus and subway networks are just not convenient enough.
I have stopped my outdoor runs. Instead, I am getting maximum mileage from a gym membership that allows me to swim as well as run.
I do miss the street scenes. But at the same time, I now can also breathe a whole lot easier, knowing that I'm not killing my lungs.