Ключевые слова: 25, acceptable, air, alert, aqi, asthma, background, block, breath, category, cause, caution, clean, concentration, danger, dirty, disease, dust, effect, emission, environment, factory, guide, guideline, hazard, health, high, illness, index, letter, level, limit, location, monitoring, pm, pollution, poor, protection, quality, respiratory, risk, root, serious, smog, smoke, standard, toxic, warning, wood, word,