Increasing trend of primary NO2 exhaust emission fraction in Hong Kong

Abstract

Despite the successful reduction in roadside NO( x ) levels, no such decrease has been detected in roadside NO(2) concentration in Hong Kong. One underlying cause could be the rising primary NO(2) fraction of the total emission of NO( x ). Primary NO(2) can be particularly detrimental to Hong Kong because a large fraction of the population are exposed to the traffic-related primary pollutants in the street canyons formed by congested high-rise buildings. In this study, hourly mean concentration data for roadside nitrogen oxides (NO( x )), nitrogen dioxide (NO(2)), and background ozone (O(3)) were used to estimate the mean primary NO(2) fraction from vehicle exhausts in Hong Kong. An overall increasing trend was observed for the primary NO(2) fraction (f-NO(2)) values in all the three roadside air monitoring sites. The primary NO(2) as a fraction of total NO( x ) (f-NO(2)) increased approximately from 2% in 1998 to 13% in 2008 in Hong Kong. The two particular periods of rising f-NO(2) coincided with the two implementation periods of the diesel retrofit programs for the light-duty vehicles and heavy-duty vehicles. Future vehicle emission control strategies should target not only total NO( x ) but also primary NO(2). Health benefit or disease burden estimates should be taken into account and updated in the process of policy planning and evaluation.

Tumor Necrosis Factor-Alpha as Biomarkers of Exposure to Indoor Pollutants Among Primary School Children in Klang Valley

“…Other epidemiology studies also reported on NO 2 as the source derived from outdoor environment Rosenlund et al, 2009;Lamsa et al, 2013), which mostly indicates urban area. It was suggested that in urban area, motor vehicle emissions are the major source of NO 2, which was also found in other studies that investigated the different levels between study areas (Tian et al, 2011;Wichmann et al, 2010).…”

Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

“…7). This finding was supported by the Hong Kong emission inventory, which indicated that the NO x emission decreased from 1997 to 2014 in Hong Kong (HKEPD, 2016), and studies conducted by Tian et al (2011) and Lau et al (2015), who found an increasing trend of primary NO 2 emission in Hong Kong due to several diesel retrofit programmes in the period 1998-2008. Apart from the regional and local impact on O 3 trends, the impact of variations of baseline O 3 was also considered. Oltmans et al (2013) reported that O 3 at mid-latitudes of the Northern Hemisphere was flat or declining during the period 1996-2010 and the limited data in the subtropical Pacific suggested very little change during the same period.…”

“…The reduction of NO titration was also confirmed by the increasing NO 2 / NO x ratio at a roadside site (Mong Kok) in Hong Kong. The NO 2 / NO x emission ratio is a parameter that can be used to examine the variation of NO titration (Carslaw, 2005;Yao et al, 2005;Dallmann et al, 2011;Tian et al, 2011;Ning et al, 2012;Lau et al, 2015). Generally, higher ratios of NO 2 / NO x mean a lower potential of O 3 titration by NO, resulting in higher O 3 .…”

Analysis of spatial and temporal patterns of on-road NO<sub>2</sub> concentrations in Hong Kong

“…In Hong Kong, vehicle emissions are the main source of NO x . Similar to many metropolitan areas, a decreasing trend of ambient and roadside NO x levels has been observed (Carslaw, 2005;Keuken et al, 2009;Tian et al, 2011) which is contributed from the effective vehicular emission control measures in the past. However, the pollution levels measured at both ambient and roadside air quality monitoring stations are still occasionally exceeded the of NO x is recorded at the roadside monitor stations in Hong Kong, which means the reduction rate of NO 2 is slower than NO in recent years (Tian et al, 2011).…”

“…Similar to many metropolitan areas, a decreasing trend of ambient and roadside NO x levels has been observed (Carslaw, 2005;Keuken et al, 2009;Tian et al, 2011) which is contributed from the effective vehicular emission control measures in the past. However, the pollution levels measured at both ambient and roadside air quality monitoring stations are still occasionally exceeded the of NO x is recorded at the roadside monitor stations in Hong Kong, which means the reduction rate of NO 2 is slower than NO in recent years (Tian et al, 2011). Vehicular NO 2 is either primarily emitted at the tail pipe or secondarily formed from oxidation of NO emission involving ozone and volatile organic compounds (VOCs) in the ambient (Muilwijk et al, 2016; 4.13 km Avantes spectrometer (AvaSpec-ULSi2048L-USB2) with a Sony ILX511 charge coupled device (CCD) detector.…”