Fine-scale spatial structure of air pollutant concentrations along bus routes

Air pollution measurements were made at 5 s intervals along a bus route in Hong Kong, chosen to avoid frequent intersections or traffic jams. This allowed periodic pollutant concentration patterns in bus-derived pollutants to be explored using Fourier analysis. The analysis showed the defining role of the bus stops in terms of NO and PM2.5 concentrations, which have profiles with a sawtooth form. Early in inter sup segmenis, concentrations are high, followed by a decline. This arises from high emissions during the acceleration away from the bus stop, then lower emissions during cruise and de-acceleration. This pattern can be enhanced on sections of the ruffle where buses are frequern as pollutants accumulate from the larger number of buses. The high conceniraLions just. beyond bus stops may have implications fur planning bus roues and the positioning of bus stops. (C) 2018 Elsevier B.V. All rights reserved.