Air quality study in Hanoi, Vietnam in 2015–2016 based on a one-year observation of NOx, O3, CO and a one-week observation of VOCs

Özet

The number of vehicles, especially motorcycles, which are the dominant source of Hanoi's air pollution, hasrapidly increased in recent decades. To investigate air quality in Hanoi, a 1-week observation of VOCs, CO andO3 in September 2015 and a year-long campaign to measure O3, NOx and CO between October 2015 andDecember 2016 were conducted in the inner city area. Overall mean values of O3, CO and NO2 mixing ratioswere 19.3 ± 15.3 ppb, 1.3 ± 0.8 ppm and 21.4 ± 11.8 ppb, respectively. The O3 mixing ratio often exceededthe WHO guideline value of 50 ppb (daily 8-h mean). Although less frequently exceeding the WHO short-term (1-h mean) guideline of 106 ppb, the observed NO2 overall mean value was greater than the WHO guideline valueof 21 ppb. A diurnal profile and analysis of the composition of VOCs indicates that atmospheric VOCs in Hanoimainly originated from motorcycles, which dominate Hanoi's vehicle fleet. The good correlation betweenmeasurements of VOCs and CO also indicates motorcycles as the main source of CO. The NOx/CO ratio, which isspecific to a given emission source, was largely unchanged throughout the year, indicating that vehicles includingmotorcycles as well as buses, trucks and cars are the main source of O3 precursors year-round. Theestimated VOC/NOx ratio of 12 ± 5 suggests that Hanoi's air quality can be categorized as NOx-limited regimewith regards to O3-formation. Therefore, controlling NOx emissions from not only motorcycles and also othervehicles would be highly effective at decreasing Hanoi's O3 levels. Furthermore, the results suggest the relationshipbetween the northeast monsoon and an O3 burst in the winter season.