High levels of NO2 can irritate the airways in the human respiratory system. Such exposures over short periods can aggravate respiratory diseases, particularly asthma, leading to hospital admissions.
So the phrase could mean:
Below are current contexts where "No. 2" is highlighted as an exclusive status in Cambodia: High-Tier Rankings & Achievements Nightlife Excellence Phnom Penh is currently ranked as the No. 2 best nightlife city in the world by certain travel and lifestyle metrics, following only National Pride : Cambodia reached No. 2 in the world no2 in khmer exclusive
According to a report by the World Health Organization (WHO), Cambodia's capital city, Phnom Penh, has some of the highest levels of NO2 in Southeast Asia. The report revealed that the city's NO2 levels exceeded the WHO's recommended limit of 40 μg/m³ (micrograms per cubic meter) by 30%. High levels of NO2 can irritate the airways