This document summarizes a presentation about RapidAIR, a new urban air quality dispersion modelling platform developed by Ricardo. RapidAIR uses an open-source python-based model that automates the workflow for modelling road traffic emissions. It can model emissions at a high resolution over large domains with computation times measured in seconds rather than hours. The model was evaluated against AERMOD and shown to produce highly similar results. Examples of RapidAIR applications to London and Beijing are presented to demonstrate its capabilities for policy analysis. Remote sensing data is also discussed and how it can be linked to dispersion models like RapidAIR.
I’m Scott Hamilton, Ricardo’s technical lead in air quality modelling here to talk to you about our new dispersion model RapidAIR,
I would like to thank the organising committee for this opportunity, I’ve a lot to get through so let’s get into it.
Some neat things it does:
Traffic emissions model built in (1 million links in 1 minute, covers NOx, fNO2, NH3, CO2, PM10, PM2.5, gradients, builds an inventory, source apportionment…)
Road dispersion model (1m resolution possible)
Street canyon model
Area source model e.g. for large dispersed sources (e.g. domestic, shipping)
Unlimited domain size and resolution (testing with 3 billion locations)
Domain splitting unlimited domain size
Met data handling- met data gathering, filling, substitution, running AERMET
Automatic handling of background values (in the UK)
Model scaling can be done automatically
Lots of utilities (data viewers, simple GIS tools etc)
Various empirical NOx NO2 chemistry options (with road NOx, fNO2 effects)
Interactive plotting (in a customisable GUI)
GUI driven option (in a customisable GUI)
Open source tools and programming languages are revolutionising industries which rely on data, the power of the tools that are available to anyone free of charge is staggering, and the capacity to innovate using them is unlimited. In our small corner of the data space we use a host of excellent open source tools to do our work. The contributions of these developers and groups cannot be overstated, and their value will only grow.
For example the Jupyter Notebook is changing the way scientists of all disciplines share code and collaborate. Its quickly become my group’s go to tool for any work that needs a combination of data, code and outputs; reproducibility is very easy to achieve.
Make the point about ‘time to interpretation being business critical- this is the part our clients pay us for- the models are just tools to get there
Ricardo and its technology partner OPUS Inspection, use state-of-the-art vehicle emission measurement technology to ensure that policy focuses on only the most polluting sectors of the vehicle fleet. By accurately measuring real-world driving emissions, we deliver the local insight necessary to inform the cost-effective design of low-emission policy.
Our remote sensing equipment accurately measures real-world driving emissions from thousands of vehicles, under actual driving conditions, in a short space of time and without interfering with the vehicle whose emissions are being measured.
Figure 1 shows an example of the variation in NOx with ambient temperature for a site on the A2 Old Kent Road, London in 2016. It shows that ambient concentrations of NOx markedly increase when the temperature is below 10°C. In fact, there is a factor of three increase in the concentration of NOx when temperature is reduced from 20 to 0°C. The variation of NOx (or other pollutants) with temperature varies by site, but the pattern shown in Figure 1 is typical. However, Figure 1 does disguise the influence of other important factors such as wind speed, which also tends to be lower at lower temperatures – such complexities reinforce the difficulty in establishing the different influences on the ambient concentrations.
Traditionally, almost all emission factors for road vehicle emissions assume that emissions do not vary with ambient temperature – but is that right? To help explore how emissions change with ambient temperature we have drawn upon our remote sensing database of vehicle emissions that contains emissions data across a wide range of ambient temperatures (6 to 29°C) covering many different measurement locations. I have focussed on emissions of NOx from Euro 5 and 6 diesel passenger cars.
The variation in NOx for Euro 5/6 diesel passenger cars with ambient temperature is shown in Figure 2. The most striking feature of this plot is how much ambient temperature affects the emissions from Euro 5 vehicles: there is about a 50% increase in emissions as ambient temperature drops from 25°C to 10°C. The emissions from Euro 6 vehicles is also temperature dependent albeit the absolute emissions are much lower than for Euro 5 – nevertheless the effect is still there.
It is interesting to note that many vehicle emission measurements are made in the range 20 to 30°C, such as those made as part of the Type Approval measurements. The Figure 2 histogram shows that, in London, there is a significant fraction of the year with temperatures below 20°C (in fact about 90% of the year has temperatures below 20°C). The combination of the prevalence of lower ambient temperatures in the UK and the evidence for increased emissions from Euro 5/6 diesel cars, suggests there may be reasons to suspect that emissions from these vehicles are underestimated. Moreover, the underestimation might be expected to vary by time of day with higher emissions occurring in the morning when ambient temperatures are lowest and traffic levels at their highest.
The main results are shown above for a total of 19,150 vehicles. Overall, diesel passenger car NOxis reduced by 55% between Euro 5 and Euro 6. There are greater reductions in NOx for vans and heavy-duty vehicles (HDVs). For diesel vans < 3.5 t NOx is reduced by 68% and there is a 58% reduction in NOx for HDVs between 3.5 and 7.5 t. The greatest reduction in NOx is however seen for the largest HDVs (> 12 t) where NOx is reduced by 88% between Euro V to Euro VI. The situation for buses is more mixed and is in fact very variable – overall, Euro VI buses emit 44% less NOx than Euro V buses on a fleet-weighted basis.
We made a league table of polluted famous buildings, we didn’t publish that
…including an advanced Vehicle Emissions Research Centre and in the use of Portable Emissions Measurement Systems.
The technique:
UV/Infrared beam to measure emissions – different gases absorb in different wavelength regions
Measure NO, NO2 (hence NOx), CO, HC, PM and NH3
100 scans in 0.5 seconds of exhaust plume
Emissions expressed as ratios to CO2 and through combustion equations, grammes of pollutant per unit fuel (mostly commonly g/kg)
Measure speed and acceleration of each vehicle
Photograph each vehicle to obtain number plate
Detailed cross reference with SMMT-derived databases…more than 80 vehicle characteristics, down to the colour of the vehicle!
Will soon add most recent MOT mileage data consider vehicle degradation / ageing effects on emissions
The results presented in Figure 2 show that Euro V bus emissions of NOx vary between 8.5 and 33.2 g NOx per kg fuel. However, there is proportionately a much greater range in the performance of Euro VI vehicles where the NOx varies from 0.8 to 12.3 g per kg fuel. These results warrant more investigation to explore the reasons behind the large variations seen. What is clear is that there will be very different implications for roadside NO2 concentrations depending on both the bus technology and driving conditions. For bus fleets, there are compelling reasons to make measurements of the local fleet under local operating conditions.
