Hong Kong vehicle emission changes from 2003 to 2015 in the Shing Mun Tunnel

Abstract

This study characterized motor vehicle emission rates and compositions in Hong Kong's Shing Mun tunnel (SMT) during 2015 and compared them to similar measurements from the same tunnel in 2003. Average PM 2.5 concentrations in the SMT decreased by »70% from 229.1 § 22.1 mg/m 3 in 2003 to 74.2 § 2.1 mg/m 3 in 2015. Both PM 2.5 and sulfur dioxide (SO 2 ) emission factors (EF D ) were reduced by »80% and total non-methane (NMHC) hydrocarbons EF D were reduced by 44%. These reductions are consistent with long-term trends of roadside ambient concentrations and emission inventory estimates, indicating the effectiveness of emission control measures. EF D changes between 2003 and 2015 were not statistically significant for carbon monoxide (CO), ammonia (NH 3 ), and nitrogen oxides (NO x ). Tunnel nitrogen dioxide (NO 2 ) concentrations and NO 2 /NO x volume ratios increased, indicating an increased NO 2 fraction in the primary vehicle exhaust emissions. Elemental carbon (EC) and organic matter (OM) were the most abundant PM 2.5 constituents, with EC and OM, respectively, contributing to 51 and 31% of PM 2.5 in 2003, and 35 and 28% of PM 2.5 in 2015. Average EC and OM EF D decreased by »80% from 2003 to 2015. The sulfate EF D decreased to a lesser degree (55%) and its contribution to PM 2.5 increased from 10% in 2003 to 18% in 2015, due to influences from ambient background sulfate concentrations. The contribution of geological materials to PM 2.5 increased from 2% in 2003 to 5% in 2015, signifying the importance of nontailpipe emissions.

Nitrous acid (HONO) emissions under real-world driving conditions from vehicles in a UK road tunnel

“…With a reduction in NO2 emissions from diesel vehicles overall, a decrease in HONO may also be expected in the UK. In contrast, Wang et al, (2018) reported an increase in the NO2/NOx ratio at the outlet of the Shing Mun tunnel, from 9.5% in 2003 to 16.3% in 2015. Therefore the higher HONO/NOx ratio observed in Hong Kong (Liang et al (2017)) comparedto current work may also be related to differences in primary NO2 emissions.…”

Nitrous acid (HONO) emissions under real-world driving conditions from vehicles in a UK road tunnel

“…With a reduction in NO 2 emissions from diesel vehicles overall, a decrease in HONO may also be expected in the UK. In contrast, Wang et al (2018) reported an increase in the NO 2 /NO x ratio at the outlet of the Shing Mun Tunnel, from 9.5 % in 2003 to 16.3 % in 2015. Therefore, the higher HONO/NO x ratio observed in Hong Kong (Liang et al, 2017) compared to our current work may also be related to differences in primary NO 2 emissions.…”

“…Therefore, the higher HONO/NO x ratio observed in Hong Kong (Liang et al, 2017) compared to our current work may also be related to differences in primary NO 2 emissions. It should be noted that in the study by Wang et al (2018), NO 2 was measured using a standard chemiluminescence monitor, which typically use a molybdenum converter. Molybdenum converters also convert other NO y species, such as HONO, resulting in an overestimation of the reported NO 2 .…”

“…1). Primary sources include direct emissions from combustion processes such as vehicle emissions (Kirchstetter et al, 1996;Liu et al, 2017;Rappenglück et al, 2013;Trinh et al, 2017;Xu et al, 2015), soil microbial activity (Laufs et al, 2017;Maljanen et al, 2013;Meusel et al, 2018;Oswald et al, 2013;Su et al, 2011) and biocrusts (Maier et al, 2018;Meusel et al, 2018;Weber et al, 2015). Secondary sources were thought to be dominated by the homogeneous gas phase reaction of NO and OH during the day (resulting in a null cycle with Reaction R1), and the heterogeneous production of HONO from NO 2 on surfaces at night (Calvert et al, 1994;Finlayson-Pitts et al, 2003;Jenkin et al, 1988;Kleffmann et al, 1998;Stutz et al, 2002).…”

Trends in on-road transportation, energy, and emissions

“…EPA's (2012; 2017) nearroadway monitoring requirements provide a means to "truth-test" exposure models. Tunnel studies yield insight into exhaust emissions and document improvements in emission control technologies (Ban-Weiss et al 2008;Cui et al 2018;Gaga et al 2018;Ho et al 2009;Kean, Harley, and Kendall 2003;Kirchstetter et al 1996;Wang et al 2018;Worton et al 2014). Cross-plume remote sensing (Bishop et al 2012;Bishop, Stedman, and Ashbaugh 1996;Bishop, Stedman, and Jessop 1992;Fujita et al 2012) and satellite detection from space (Hidy et al 2009;Hoff and Christopher 2009) have also increased knowledge of the near-roadway environment, the effectiveness of emission controls, and emission decreases over time.…”