Looking at people who have had lung surgery or are undergoing chemotherapy, many are quite sensitive to outdoor fine dust yet let the air inside the house slide. The truth is, the place where we spend most of the day is home. Counting sleeping hours too, the time spent indoors is overwhelmingly long. So if you want to ease the respiratory burden on someone receiving treatment, it may make sense to look after the air in your own living room and bedroom first, before the weather outside.
What actually makes the air inside the house bad is nothing grand. The smoke from grilling meat on the gas stove, the dust that flies up while cleaning, scented candles and air fresheners, and above all, cigarette smoke. Even if you yourself have quit, if a family member smokes on the balcony or in the bathroom, that smoke eventually comes back into the house. In front of someone receiving treatment, "secondhand smoke" is far more harmful than people think. The whole family quitting together, or at the very least keeping a distance and smoking outside, then changing clothes before coming in — that level of consideration is essential.
When cooking, cut down a bit on the frequency of grilling or frying over high heat, and run the hood from the moment you turn the gas stove on until you turn it off. Surprisingly, many people turn the hood on after the food is fully cooked, but turning it on after the smoke has already spread is too late. Turning it on the moment you start cooking is the key. As for ventilation, it is good to open the windows so a cross-breeze passes through, even briefly, two or three times a day, morning and evening. On days when outdoor fine dust is severe, instead of window ventilation you can use a device with a ventilation function, or open the windows briefly and then immediately run the air purifier.
If you use an air purifier, it is good to choose a model with a HEPA filter and a capacity that matches the area of the space you mainly use. Putting one that is too small in a large living room essentially makes it an ornament. And you must not rely on the machine alone and forget to change the filter. A clogged filter can hold dust and then blow it back out, so change it on the cycle the manufacturer recommends. When using a humidifier in winter, you also need to empty and clean the water tank often. Otherwise, bacteria spread straight into the air.
When going out, it is good to build the habit of checking the fine dust forecast once. On days when the readings are bad, shift your plans indoors altogether, or if you must go out, bring a health mask such as a KF94. However, for someone who gets short of breath or whose oxygen saturation drops, wearing a mask itself can make breathing even harder, so it is safer not to overdo it and to keep outings short. When you come home, just washing your hands, shaking off your outer clothes, and leaving them near the entrance can do a fair amount to keep fine dust from being dragged all the way into the bedroom.
Rather than equipping yourself with grand devices, these small habits — minding the timing of ventilation, keeping cigarette smoke far away, and changing filters on time — building up every day make a bigger difference. That said, if shortness of breath suddenly worsens, or the color of your phlegm changes and you have a fever, don't just blame the air; be sure to consult your attending physician. Don't forget that this article is only a story of general lifestyle care, and judgments suited to each person's condition are the role of the medical team in charge.