Exposure to nitrogen dioxide (NO2) before getting a cold can make asthma worse in children. The study looked at 114 kids with asthma, tracking their symptoms and NO2 levels. Higher NO2 levels before a cold led to more severe asthma symptoms. NO2 can come from things like gas stoves or fireplaces. The study found that NO2 levels within safety limits didn't cause problems, but high levels during a cold made asthma worse.