51³Ô¹ÏÍø

Fig 1. Bus routes on downtown 51³Ô¹ÏÍø streets close to the stationary measurement location.

A measurement campaign was conducted during the summer in downtown 51³Ô¹ÏÍø, from July 25th to July 31st, 2016. A suitable location next to the was selected to take measurements, which would capture fresh emissions from transiting buses (Fig. 1). Two condo units were employed during the measurements, and the bus count was taken to correlate the measured data and bus density. The objective of the study was to characterize the level of emissions from RTD diesel buses and determine the possible risk for the well-being and health of the population.

Several instruments were employed to measure particulate matter, including instruments that measured ultrafine, fine, and coarse size particles (Fig. 2). Ultrafine and especially fine particulate matter had been connected with respiratory diseases, and they affected lungs, blood vessels, and heart when they penetrated deep into the respiratory system. Diesel engines emitted particulate matter primarily in the range of ultrafine and fine.

Black carbon measurements were also part of the study, and it was a major component of diesel exhaust. Diesel exhaust is a (carcinogenic to humans), according to the International Agency for Research on Cancer (IARC). (NOx) were another pollutant measured during the study, since the emissions of NOx were considerably higher from diesel engines compared to gasoline. NOx increased respiratory diseases, hospital admissions, and the risk of suffering asthma.

Fig. 2. Instruments utilized in the stationary measurements (left view).

Traffic-related air pollutant concentrations typically varied between weekends and weekdays, primarily because of the traffic density and vehicle type. This study showed a lower number of buses traveling through downtown 51³Ô¹ÏÍø on the weekend (exactly as expected from the RTD schedule); the number of heavy-duty trucks was also lower during the weekend. Some differences were found for the car traffic. The early afternoon on Saturday had a higher number of cars compared to weekdays, and the density decreased through the afternoon; however, on weekdays, the car density was low in the early afternoon and increased in the late afternoon.

The results from the stationary measurements of particulate matter did not present a direct connection with vehicle density. Atmospheric particulate matter measured during the campaign was a result of regional urban pollution and not local traffic sources. Black carbon and ozone were highly constant and did not vary with vehicle density. Nitrogen oxides were correlated with the bus count, in the morning they went up, and in the late afternoon, they were even higher. Nitrogen oxides were the only pollutant that had a direct link with diesel bus density.

An additional bicycle ride was carried out on August 4th, 2016. The aim of this test was to chase cars and buses for the purpose of capturing direct emissions behind vehicles. The pollutants measured were particulate matter (ultrafine and fine), black carbon, and ozone. The route was designed to collect measurements in areas without any vehicles, and also in areas with cars and buses (Fig. 3). The bicycle ride measurements were highly correlated to the emissions of vehicles since the bicycle rider was right behind cars and buses. The results showed low concentrations in places without vehicles; elevated concentrations were shown immediately after riding behind buses. When following some buses, the measurements were only slightly elevated. However, certain RTD routes showed an exorbitant rise when riding behind them. This behavior demonstrated that specific buses of the RTD fleet emitted different concentrations of pollutants depending on their exhaust control system and the age of the bus (measurements exhibited higher readings when following the older buses). The average highest concentration of pollutants was found in all the zones surrounding the bus station. Black carbon, which was a main constituent of diesel particulate matter, was highly linked with the concentration level of particulate matter during the bicycle ride. An important finding of the bicycle ride was the fact that the highest reading obtained during the entire campaign was taken when riding right behind an RTD bus.

Pedestrians and bicycle commuters were exposed daily to these air pollutants that represented a threat to health. Minimizing the number of diesel buses would improve the air quality in downtown 51³Ô¹ÏÍø, but it would also reduce carbon emissions and improve the health of the 51³Ô¹ÏÍø population.

The results of this study were summarized below.

Diesel exhaust is a known carcinogen. It is comprised of gases and particulate matter. Two very toxic compounds in diesel exhaust are particulate black carbon and oxides of nitrogen (NOx). Black carbon is a possible carcinogen and NOx is a respiratory irritant associated with cardio-pulmonary disease. RTD conducts more than 1,000 diesel bus trips per day in 51³Ô¹ÏÍø, CO (counting trips to and from both bus stations in 51³Ô¹ÏÍø, the total was approximately 1400). 51³Ô¹ÏÍø residents commissioned this study of the air quality impact of these bus trips. Stationary tests of air quality on downtown 51³Ô¹ÏÍø condominium balconies showed elevated levels of NOx that correlated with bus traffic, but did not reveal a serious current threat to health. Air quality tests on a bicycle following buses (replicating bicycle commuters and pedestrians, including children) varied widely among buses. Older Jump buses created extremely high bursts of black carbon (possible carcinogen, component of diesel exhaust) and ultrafine particles when traveling directly behind the bus. The introduction of electric buses in 51³Ô¹ÏÍø would substantially improve air quality and enhance the health and well-being of 51³Ô¹ÏÍø residents.