Guest post by our two former Bachelor students Simon Moser and Lucas Spring
To better understand the urban heat island effect (UHIE) and to be able to plan urban heat mitigation measures in a more targeted way, high-resolution models of the temperature distribution in cities are needed. An important component to develop and validate such models are in-situ measurements with a network of temperature stations as dense as possible. The construction of such a network often fails due to the high costs of ownership since precise measuring stations are expensive. This problem was tackled by two students in their bachelor thesis, in which they took up the challenge of developing a measuring station for RH and T from scratch (Fig. 1). The biggest difficulty from a measurement point of view was to keep the radiation error small, for which they developed a new measurement method.
Fig. 1: Measurement station as designed by the students.
Existing measuring stations on the market are mostly permanently ventilated and expensive or have a high radiation error. Since the newly developed station had to be inexpensive and sturdy, it was necessary to design an independent power source, because it would be too expensive to connect each station to the power grid. As well, because the station is designed to capture the UHIE, a high absolute accuracy was required.
The developed measurement method, which is supposed to be energy-saving and precise at the same time, is based on the system theory of linear time-invariant (LTI) systems. A small fan was installed to ventilate the temperature sensor. However, the fan is not operated permanently, but only intermittently over short times. Switching on the fan causes step response of the system. Experiments in the laboratory showed that this system response is linear to the radiation error (second order system). This means that one can predict the behavior of the measuring station by observing the system response. This way the correct temperature reading can be extrapolated a long time before the fan has had a chance to equilibrate the system entirely. This results in a greatly reduced runtime of the fan (30 s per measurement) and thus a highly efficient use of energy.
In another experiment, two prototypes of the developed measurement station were operated in parallel with a reference measurement station (ventilated Lufft WS800 UMB) to determine the extrapolation parameters. By means of an equalization calculation, these parameters were determined and applied to the same measurement data. This led to a significant reduction of the radiation error and to a high absolute accuracy (Fig. 2).
Fig. 2: Temperature differences w.r.t. the reference station. Blue: uncorrected. Red: Ventilated, after 30 seconds. Orange: Corrected using the new algorithm.
Nevertheless, the extrapolation of further measured values with the same extrapolation parameters resulted in values that, in some cases, deviated strongly from the reference values . The students speculate that the influence of the wind on the open radiation shield causes a nonlinear behavior of the system. To better investigate this effect and to improve the developed measurement method, a further prototype is to be built in upcoming research work, which should behave as linearly as possible even in variable wind situations.
Guest post of our two Bachelor students Soneesh Gill and Manuel Walter
The study of urban heat islands becomes more and more important, especially when considering the ongoing climate change. To keep urban regions habitable in the future, city planning measures must be taken. To achieve their greatest benefit, measures such as the greening of urban districts or the construction of fountains and other water features must be placed at appropriate locations.
Most conventional measuring devices used to detect urban heat islands are stationary in-situ sensors. The Zurich University of Applied Sciences (ZHAW) also operates such a network of nearly 300 sensors in the city of Zurich. However, in order to close data gaps and to be able to make statements about the entire urban area, a mobile temperature and humidity measuring device is helpful.
This is where our bachelor’s thesis should generate an additional value: In a first phase, a prototype of a mobile measuring device has been developed. In the current phase, this prototype will be placed on PubliBike e-bikes and will collect data throughout the city of Zurich. The measuring device records not only temperature and humidity values, but also assigns GPS location data to each measurement. This allows to display the prevailing temperature and humidity on a map (Fig.1).
Figure 1: Measured relative humidity (left) and air temperature (right) during a bike ride in the evening of November 12th, 2020.
Respecting the privacy of PubliBike cyclists is of great concern to us. Therefore, we made sure that the meteorological data and the riders’ data are stored within two physically separated systems, making any meteorological measurement entirely anonymous.
In the future, the goal is to draw meaningful conclusions from collected data and therefore help decide on city planning measures. To achieve this goal, the developed device must be continuously improved and a large number of PubliBikes shall be equipped with the measuring device. In addition to temperature and humidity logging, the functions of the device could also be expanded in the future, allowing the monitoring of values such as carbon dioxide levels or particulate matter concentration.
Particle emissions of small turbine engines are unknown and unregulated
Jet engines for commercial airliners in production now and in the future are certified for particle emissions from a virtual landing and take-off cycle. However, one potentially large group of engines is left out. Small jet engines (<26.7 kN rated thrust), found on business jets, as well as other types of turbine engines used in helicopters and propeller-powered aircraft have only to pass an old-fashioned exhaust smoke visibility test. Although these unregulated engines burn a small fraction of the world’s jet fuel, there are concerns about their contribution to local air pollution. Small turbine engines have therefore appeared in the spotlight of regulatory agencies and researchers. Unlike the grounded commercial fleet, private jet traffic has been resilient and increasing in many places in the second half of 2020.
Swiss “Air Force One” underwent an emissions test using a unique measurement system
To fill the knowledge gap in particle emissions of business jets, together with my colleagues from Empa at the time, we performed an emissions test on the Dassault Falcon 900EX of the Swiss Air Force, a VIP transport plane of the federal government. This modern plane is equipped with engines, which are widely used around the world. The test campaign was possible thanks to the Swiss Air Force’s support and coordination by Mr. Theo Rindlisbacher from the Swiss Federal Office of Civil Aviation (FOCA). This campaign marked the first deployment of the Swiss Mobile Aircraft Emissions Measurement System (SMARTEMIS). SMARTEMIS is one of the three reference systems in the world for measuring nonvolatile particulate matter emissions. For the emission tests, a forklift held a custom-built exhaust probe right behind the center engine. With the brakes applied, the pilot put the engine through a test cycle from maximum power down to idle several times. The exhaust sample was transported via heated lines to the instruments placed more than 25 meters away inside a hangar.
Sunrise behind the Falcon 900 with the exhaust sampling and measurement equipment installed.
Small plane – low emissions?
The jet engine on the Falcon 900 burns approximately 20% of the fuel needed by a Boeing 737 engine; thus, one can expect the overall pollutant emissions to be proportionally lower. However, for the standard LTO cycle and per aircraft, the small Falcon 900 emitted more particles, both in terms of mass and number, than a Boeing 737. Most importantly, for health effects, the highest number of particles was emitted at low power applied for ground movements. Since aircraft are designed to spend most of the time in the air and not on the ground, I developed an engine performance model to correct the ground test data to estimate the particle emissions during the flight. The estimated particle emissions per flight hour at cruise altitude were found to be in the range found previously for large commercial aircraft.
More work underway to get the bigger picture
This study reports the first nvPM emissions for a business jet engine measured using the standardized methodology. Since only one aircraft type was measured, one should not extrapolate the results to the entire fleet (as some modelers are often tempted to do so). Since the Falcon 900 tests, SMARTEMIS has been deployed behind another business jet, and more tests are planned in Switzerland and abroad. We have been also improving our models for correcting ground measurements to cruise.
Reference
Durdina, L., Brem, B. T., Schönenberger, D., Siegerist, F., Anet, J. G., & Rindlisbacher, T. (2019). Nonvolatile Particulate Matter Emissions of a Business Jet Measured at Ground Level and Estimated for Cruising Altitudes. Environmental Science and Technology, 53(21), 12865–12872. https://doi.org/10.1021/acs.est.9b02513
As you saw in the last blogpost, our group is maintaining a high resolution temperature and humidity monitoring network in the city of Zurich. Some of the stations are also located in the district of Zurich West, which is located just north of the railroad tracks running towards the main station. Zurich West is quite special in a sense that it consists of mostly built-up areas. Most of the district is made up by impervious surfaces, which all contribute overproportionnaly to the urban heat island effect. We were approached by the City of Zurich regarding urban climate simulations of Zurich West, with the goal to find out how heat stress indices would change if certain mitigation actions were taken in this particular area. The goal was to present some results in the architecture magazine “Hochparterre”, for which the simulations had to be ready within a relatively short time frame. We gladly accepted the challenge.
We went on to simulate the changes e.g. in the physiological equivalent temperatures (PET), which is an index for thermal comfort for an individual. Looking at the results for the PET, we can indeed say that it was hot on the simulated day (26.06.2019, 14:00h). Thermal stress reaches a very high level, which is plausible given that the simulated day lies within one of the heat waves of 2019.
Simulated PET at 2 o’clock in the afternoon on the 26th of June 2019.
The mitigation actions that were then implemented in the simulations on a large scale were i) an implementation of green roofs, ii) increasing albedo values of surfaces and facades, iii) the de-sealing of impervious surfaces to grass/gravel mix or just grass and iv) a combination of the above.
The results we got were most interesting. From the results of the simulations we could see that the de-sealing of surfaces seems to decrease PET the most (up to -4 to -6°) out of the simulated options.
Changes in PET by de-sealing surfaces.
What is very interesting though is the change when surfaces are made brighter, i.e. the albedo value of surfaces is increased. The results show a remarkable increase in PET values during the day when increasing surface albedos. This equates to an increase in thermal stress, so a decrease in thermal comfort for pedestrians walking in the area during that time.
PET change during the day due to increased surface albedos.
This is quite counterintuitive – one would expect temperatures to drop when making things more bright! When looking only at the simulated air temperature values, the latter can be confirmed: Air temperature actually decreases in this scenario. So how can we reconcile the decreasing air temperature and the increase in heat stress? The cause for this effect can be found in the change of radiation fluxes: When increasing the albedo values of a surface, less shortwave radiation is absorbed, which leads to lower surface and lower air temperatures. However, this also means that much more radiation is reflected and irradiates pedestrians, who effectively will be fried from above, by the sun, and also a bit from below, by the reflected radiation from the soil. In the end, the decrease in longwave radiation due to the decrease in surface temperature is not enough to offset the increase in reflected shortwave radiation during the day, leading to the increase in thermal stress for the public. This mechanism is supported by various studies. During the night though, when the solar radiation is no longer a factor, the decreased surface temperatures lead to a decrease in air temperature, and thus also to a decrease in PET during the night.
So what does that all mean in the end? It clearly tells us that mitigation actions do not always act in an intuitive way, given the results of the albedo change. With the skills we developed in our team, we are able to simulate these effects. Combining this ability with the measurements mentioned in the beginning, we can combine the relevant topics required for successful urban climate research, and continue the quest of trying to improve our future lives in cities.
Even if COVID-19 has currently pushed global warming out of the media and thus partly out of our minds, this does not mean that it is no longer a threat. Especially now, with the beginning of the warmest months of the year in the northern hemisphere, many people will be experiencing an ungentle reminder of one of the worlds most urgent problems . One of the reasons for this is that more than half of the world’s population now lives in cities (2018: global ~55%, Switzerland ~75%), which are particularly affected because of the so-called urban heat island effect (e.g. Rizwan et al., 2008 or Ward et al., 2016 ).
In order to investigate this effect in more detail and above all to be able to make better temperature forecasts, we have installed a high-resolution measurement network in the city of Zurich together with the Institute of Data Analysis and Process Design (IDP) and our industrial partner meteoblue as part of an Innosuisse project. After consultation with the local transport company (VBZ) and energy service provider (ewz), we were allowed to use their catenary masts or lighting masts as a mounting option.
We installed almost three hundred sensors that are regularly distributed throughout the city, using two different devices. At every third location a LoRAIN measuring station is mounted. This device, produced by Pessl Instruments, measures air temperature, relative humidity and precipitation and automatically transfers the data via LoRaWAN to our database. The power supply is provided by a small solar cell and a supercap. For project optimization, a low-cost version with a self-engineered customized radiation protection was installed at the remaining locations, whereby the used sensors (Smartgadget SHT31) were sponsored by Sensirion AG. The idea and the design of the radiation protection was developed by Moritz Gubler from the University of Bern who has already used it for similar measurements but with different sensors in the city of Bern. The Smartgadget records temperature and relative humidity and is powered by a battery. As a drawback, the data must be read out on site manually.
Low-cost version with self-made radiation protection and Smartgadget SHT31 inside (left) and LoRAIN (right)
Since we installed the sensors in the city last summer, problems have arisen with both variants. From excessive dirt, short circuits and firmware problems to vandalism and transmission failures, everything has happened. But due to the large number of stations and thanks to the two different variants we never had a total failure of the measuring network and we could therefore collect valuable data and experience already in the first year. In the meantime, we could solve most of the problems and are ready to measure the heat stress in summer 2020 in the city of Zurich in unprecedented horizontal resolution.
For a few months now, our group and our students have been doing field measurements using Partector 2, a portable particulate matter (PM) sensor from naneos particle solutions gmbh. This very nice portable device utilizing induced currents (Fierz et al, 2014) measures the lung-deposited surface area (LDSA, see e.g. the paper of Sager & Castranova, 2009), average particle size and particle number concentration. It also provides the calculated mass concentrations of particles smaller than 300 nm, all at 1 Hz frequency.
The Partector data tend to agree well with data from other more complex, bulky and costly instruments based on differential mobility measurements and particle counting (e.g. the SMPS). Yet, both types of instruments, of course, have their right to exist, as their respective field of application differs significantly. Portable instruments, such as the Partector, are the future of air quality monitoring.
While current air quality regulations limit the mass concentration of particles below an aerodynamic diameter of 10 micrometers (PM10) or 2.5 micrometers (PM2.5), particle numbers or potential inhalation hazards are not yet considered. However, most soot particles (in terms of their count) formed during the combustion in all types of engines are typically smaller than 0.3 micrometers (Burtscher et al., 1998, Czerwinski et al., 2017 or Jonsdottir et al., 2019). Such small particles have a very high ratio of their surface area to their mass concentration. Biologists and lung toxicologists agree that particle surface area (and thus LDSA) is the most relevant metric for acute lung toxicity (Schmid and Stoeger, 2016).
Dr. Martin Fierz, physicist and founder of naneos particle solutions, is convinced that LDSA has, up to now, been underestimated as a meaningful metric for air quality; so are we.
Left: Installation of an LDSA-Box on a roof near Zurich. Right: LDSA box in a rural setting
We thus couldn’t resist when he offered to let us test a new product: an LDSA monitor in a rugged enclosure designed for long-term ambient measurements. In collaboration with the city of Zurich (thanks to Dr. Amewu A. Mensah), and with the contribution of the Swiss Federal Laboratories for Materials Science and Technology (thanks to Dr. Christoph Hüglin), we rapidly deployed a network of ten of these new “LDSA-Boxes”. Eight boxes are located within the city of Zurich and its suburbs, while two of the LDSA-Boxes are installed in rural areas.
The LDSA-Boxes can be monitored online and seem to do a fantastic job up till now. We’re looking forward to seeing the effect of the step-wise return to “normal conditions” out of the partial lockdown on LDSA in Zurich!
A great thanks to the entire naneos team!
Snapshot of live LDSA data (not yet quality-checked)
Of course, COVID-19 also affected us, leading to working from home, interruption of routine aircraft turbine emission measurements at SR Technics, or to additional workload linked to remote teaching activities.
On a positive note, COVID-19 offered the unique situation of drastic reductions in road as well as air traffic. At Zurich airport, there were days with less than 10% of the usual number of aircraft movements! While the sudden reduction of noise from approaching and departing aircraft was immediately noticed (we guess, with satisfaction) by those living in the neighborhood of the airport, we preferred to focus on our specialization: Air quality.
Stopping our emission measurement activities at the SR Technics facility meant that all our instruments were available for immissions measurement in the surroundings of the airport. We skipped the dilution step used in direct exhaust sampling and configured our instruments to sample ambient air. We measured a wide range of pollutants, such as carbon monoxide, hydrocarbons, nitrogen oxides, volatile and non-volatile particles in the size range from a few nanometers up to ten micrometers.
Due to various circumstances, we waited for meteorological conditions with a dominant SW-W wind direction. Yet, during a long time frame of the soft lockdown situation in Switzerland, a solid “Bise” – a typical NE-blowing wind in Switzerland – prevented any sensible campaigns. But as always, good things come to those who wait; finally, a short 3-day window of opportunity with weak westerly winds appeared.
We packed everything up and managed to install our instruments in the vicinity of the airport within a few hours.
Left: Installing the PM2.5-inlet. Middle: Lovely evening mood, yet too quiet for our ears. Right: Aboard our “EMIS-VAN”
For 48 hours, we continuously monitored our instruments and recorded a nice set of very interesting and unique data.
While a thorough analysis and some additional datasets are required, we’re just very thankful that this tiring and intense, yet short campaign could take place.
I had the pleasure of attending the PALM-Seminar 2020, probably the one which has attracted the largest number of attendees so far. Find out in the following article how it went.
Neues Ratshaus in Hannover, next to the PALM-Logo.
In the beginning of February, I was given the opportunity to attend the PALM-Seminar at the Leibniz University in Hannover. PALM is a Large Eddy Simulation weather model specifically made for microscale simulations of the planetary boundary layer and urban climate. Although there has been quite some work at the Center for Aviation with PALM already, mostly in the scope of two semester projects and my Master Thesis, I was extremely excited to be able to attend this seminar. The PALM-Seminar is intended to give an insight into technical details about the model, how it is operated and how output is interpreted. But my main motivation for attending was my conviction that there is no better way to learn something than being on site with the experts and asking “stupid” questions or clarifying things that are done in a certain way, because of just not knowing any better.
For that, I started my journey on Sunday, February 9th, from Winterthur towards Hannover. Having studied Aviation at the ZHAW, I love taking a plane to get around. However, the increasingly widespread discussions about the environmental responsibility of each and every one of us did not leave me unscathed. So, I gave the Deutsche Bahn a try. A few days before the trip, the storm Sabine was announced to have a huge impact on Europe, starting in Germany on the very Sunday I was intending to travel. On the day of travelling, I nervously took an earlier train than originally booked, only to learn in Zurich that it never got past Basel on its way into Switzerland. A short run later, I was in the Interregio towards Basel SBB, where I learned on arrival that it never even made it there either; another train was waiting in Basel Badisch Bahnhof. A short tram trip later, I sat in my reserved seat in the ICE. Anxiously awaiting what the travel gods might throw my way next with the approaching storm Sabine, I could not really relax. But, all worrying was for nothing, I arrived in Hannover with the usual 15 min delay. Fun fact, my originally booked train arrived in Hannover without any delay or problems.
Hannover Hauptbahnhof just before DB-Fernverkehr was stopped for good due to weather.
Other participants didn’t make it though. At 18:00, the DB stopped all long distance trains in major train stations due to the weather. My summary from a traveling point of view – I am happy I took the train, because the flights on that day to Hannover were cancelled. However, while the seats might be a bit more comfy and leg space be more generous in the train – having to sit in them for seven hours compared to an hour on the plane definitely takes a toll. Yet, it would have been ironic not to make it to a weather model seminar due to weather.
On Monday morning, the seminar started. Unfortunately, 18 people did not make it to Hannover in time for the first day due to cancelled flights and the Corona virus outbreak in China, nevertheless a lot of people attended the seminar. The first day was already very interesting. It started with a repetition of LES theory and its application with valuable tips here and there, which one would not learn from looking at the lecture slides alone.
The way to go these days.
Monday’s exercise covered the very basics from the installation of PALM to a simple, flat-terrain simulation. As someone who has done both quite a few times already, I spent the time helping others and toying with parameters. The day ended with a get-together apéro at the Institute for Meteorology and Climate with interesting conversations about PALM and other people’s intentions in their PhD projects and planned applications. The majority of attendees are part of the German UC2-Project (Urban climate under change), which is ongoing at multiple German universities and weather services.
Day two continued with lectures about the numerics, boundary conditions and code parallelization paradigms applied in the PALM model system, giving a thorough insight about why things are done in the way they are. A lecture about the topography implementation in PALM was naturally of big interest to me, and judging from the amount of questions that arose from the audience, it was of general interest. Surely, the ability to resolve topography on a Cartesian grid is one of the attractive features of PALM. For me, the highlight of the day was a quick talk with Helge, who is part of the PALM team and is working on gust and fog modeling near airports. Seeing what is possible regarding gust and especially fog modeling with PALM, while still under development as part of his PhD project, was amazing. The expectation of having fog modelling implemented in PALM in the future, opens new interesting fields of applications for PALM. Exciting times are ahead.
On the third day, the topics presented were totally new to me: we focused on user code and on the wind turbine model. The ability to supply individual user code is a strength of PALM. This offers new possibilities for prognostic equations or it can simply be used to program special output variables. I was especially impressed by the possibilities the user has when applying the wind turbine model. PALM employs an actuator disc model with rotation, allowing the user to individually define the geometry of the blades used in the model. That includes the airfoil positions along the blade span, providing lift and drag polars etc. Compared with a simple actuator disc model, this results in the up- and downward motions in a turbine wake to be captured in the simulated flow field. Very neat.
Issues with boundary conditions too close to objects are topics of the exercises.
Day four and day five were reserved for the various modules that PALM has to offer. The Land Surface Model, Urban Surface Model, Plant Canopy Model, Radiation Models are all essential models, or modules respectively, when trying to simulate the complex urban environments of today’s cities. The sheer amount of work that went into these models is amazing. Facades of urban buildings can be parameterized by no less than 136 parameters – luckily, there are bulk parameterizations available, as getting all these data is almost impossible for individual projects, if it’s not a big one. In that sense, it is obvious that all these efforts are being made in the scope of the UC2 project for simulating urban climates in German cities for which work is done towards getting all these data more or less available.
Day four was personally extremely helpful, as the exercises of today dealt with creating a user defined variable for output. While PALM allows outputting many variables already, some that would also be conveniently calculated online while running the simulation have to be implemented by the user himself. For me, not knowing Fortran all that well, it was a challenge just to create a simple output variable for horizontal wind speed – but once the general structure is known, it is already much easier. A very helpful exercise indeed. This was done in the context of an exercise applying the land surface model, in which also a diurnal cycle with dew formation during night was simulated.
The last day brought some more information regarding the chemistry model implementation, which is available in PALM. Multiple chemistry mechanisms can be created with a PALM-specific implementation of the Kinetic PreProcessor, which is a widespread tool in atmospheric chemistry models and also used in WRF-CHEM. Various chemistry mechanisms are already created and readily available for use in PALM. For example, a photo-stationary state with the three compounds NO, NO2 and O3 (+ a passive tracer, PM10) or a photochemical mechanism for smog. Together with PALM, it will be possible to do emission simulations on building block scale, which is very innovative. Right now, surface emissions are implemented, with point sources planned to be implemented in the future. This will be interesting for our group as well. It will be interesting to see how and if it can be applied also to aircraft emissions.
Herrenhäuser Gärten, right next to where the PALM Seminar took place.
An exercise and some interesting discussions with other attendees later, the good-bye lecture took place. The lecture outlined what we learned during the week, and what we did not learn – there is no way to present the whole model system in just one week. An outlook into future features was given as well, which was quite a long list in the end. We will probably be getting a new output module in 2020, alongside an immersive boundary condition, allowing smoother topography than what is implemented the current castellated approach. But what was extremely exciting for me to hear, was that a way to run PALM in the cloud is being worked on. This may potentially be a huge blessing to operating PALM in the field regarding now-casting. All in all, exciting times are ahead of us.
As I’m sitting now in the train, home bound, I can’t help but reflect on the last week in Hannover. It has been an exciting, eye-opening week and it was amazing to see and hear what people are intending to do with the simulation model that I had the pleasure of learning from scratch in the last year in near-isolation from other like(palm-)minded people. It was extremely interesting to hear from people who are dealing with similar issues like me, for example with input data processing or data acquisition, and learn from their approaches and get new ideas about how to do things differently. Contact info with partners in crime from various entities were exchanged – the PALM community is definitely alive. I realized that the potential of the model is huge. With the prospect of it turning into a community model at some stage in time, PALM might have a bright future ahead of it. It is now up to us to do thorough, interesting work and try to apply PALM in areas it is intended for and produce meaningful results.
On January 13-17, 2020, Julien and I attended the meeting of the SAE E-31 Committee, which took place in the historic Glamorgan Building of Cardiff University (little did I know that it would be the only face-to-face meeting the committee would have this year…). As usual, the first day of the meeting was devoted to the contributions of the bleed air subcommittee, which develops practices and standards for cabin air quality testing. The remaining days were taken by the gaseous and particulate subcommittee, where I am a member.
Entrance of the Glamorgan Building of Cardiff University.
During the meeting, I presented two works:
The first, which I prepared together with Dr. Eliot Durand, the main author, dealt with particle size distribution properties of non-volatile PM (nvPM) emissions of various commercial turbofan engines. We also analyzed the use of particle size distribution for calculating particle losses in nvPM sampling and measurement systems. For that, we combined data sets from our team (SMARTEMIS data) and the Cardiff University team who operates the European nvPM reference system. Together, we have data for a wide range of engines, ranging from small business jet engines to the largest commercial turbofans. Once we get it published, this will be a unique piece of work (and hopefully handy for modelers!).
In my second contribution, I looked at ambient temperature effects on nvPM emissions. This topic is essential both from the regulatory perspective as well as from the scientific one. When aircraft engines are certified for emissions (gaseous and particles), the engine test points are usually set using the combustor inlet temperature corresponding to a given thrust at sea level in the international standard atmosphere. However, ambient temperature (and pressure) variability affects other thermodynamic parameters in the engine. For emissions, we mainly look at the combustor inlet pressure and the total fuel-air ratio at the combustor exit. Let’s say we run the same engine at high thrust at the same combustor inlet temperature at 25 °C and at 5 °C. At 5 °C, the pressure at the combustor inlet would be approx. 30% higher, and the fuel-air ratio would be approx. 5% higher than at 25 °C. Depending on the nvPM emission characteristic of the engine, this could lead easily to a 50% higher emission index (amount emitted per kg fuel burned). Luckily, we do have such datasets from previous test campaigns done at SR Technics, and we have tried various correction methodologies developed within ICAO CAEP. The correction for ambient conditions is also very important for estimating aircraft emissions during the flight from ground test data (only a very few emission tests have been done at cruising altitudes).
The meeting gave us a chance to network with our colleagues and also to explore Cardiff and its history. We went on a tour of the Cardiff Castle, followed by a Welsh Banquet in the Undercroft (traditional food accompanied by live music and entertainment).
Dining hall in Cardiff Castle visited during the tour.
The meeting concluded with a tour of the facilities of the Gas Turbine Research Centre (GTRC). GTRC operates a high-pressure combustor rig, which will be used during our tests with SMARTEMIS there in the framework of the RAPTOR project.
Optical measurement section of the high pressure combustor rig at GTRC.
We are grateful to Dr. Andrew Crayford, Dr. Eliot Durand, and their co-workers at Cardiff University and GTRC for hosting this meeting!
It is uncommon to get such a nice view of the Golden Gate Bridge without fog (photographed from the top of Coit tower).
…make sure your poster tube fits in the overhead bin. On December 7, 2019, I was boarding a flight to San Francisco to attend the AGU Fall Meeting (American Geophysical Union). And judging by the frequent occurrence of poster tubes sticking up in the line of passengers waiting to board the plane, I was by far not the only one. My neighbor on the plane, a postdoc from the UK, an atmospheric scientist, was also going to the same place. Seeing so many scientists on just one plane made me realize the monstrous proportions of this event: around 25’000 participants from all around the world were expected to attend the 100th AGU fall meeting. AGU encompasses a wide range of subjects related to our planet and beyond. I was going there as a poster presenter and a co-chair of a session on aircraft emissions.
Keynote lecture given by the former NASA astronaut, Dr. Mae Jemison.
Back in April 2019, I was asked by a colleague from NASA Langley, Rich Moore, whom I briefly got to know a few years ago (at another conference), to co-chair a session on aircraft emissions at the AGU. I had heard about the AGU (especially about its proportions) but never attended before. Our first mission as session chairs (we were four, including Christiane Voigt from DLR and Rick Miake-Lye from Aerodyne research) was to invite people to submit contributions. We received about 30 contributions, from which we picked 8 oral presentations and the rest were assigned as poster presentations (including all session chairs). We submitted our program to the program committee by the end of August. At the beginning of October, I received a confirmation e-mail about the acceptance of my presentation and invitation to serve as a chair for the session. AGU was a go!
With an event of such size, you need a proper venue. The conference took place in the freshly rebuilt Moscone convention center. The center has three wings (South, North, and West) and the poster sessions were held in a massive underground hall between the South and North wings with several thousand posters being presented on a given day and overall, more than 7000 presentations were given during the conference.
One of the lecture halls used for keynote speeches.
The speakers in our session “Aircraft engine emissions impacts on air quality, cloud formation and climate” gave high-quality presentations on a wide variety of subjects related to environmental impacts of air travel: ground emission measurements, airborne measurements, alternative fuel effects on emissions, contrails modeling, ambient air monitoring and novel instrumentation. Overall, the session was well attended and the audience asked intriguing questions. It went by all too quickly: only 15 minutes per talk including questions. That is why I usually get more out of a poster session.
Program of the session on aviation emissions.
My poster dealt with a comparison of measured emissions of non-volatile particulate matter (the solid component of soot composed of light-absorbing carbon, also known as black carbon) from a wide range of aircraft engines with a method based on emissions certification data. Our results show that in-service engines can widely vary in terms of their emissions profile and often have higher particle emissions than the estimates based on their certified smoke number (a measure of exhaust smoke visibility), especially in terms of the particle number emissions (number of particles emitted per kg fuel burned). Getting the best possible answers is crucial for scientific assessments of environmental impacts. Investigating the effects of engine aging on emissions and emissions variability is the focus of our project AGEAIR.
Lukas in front of his poster.
Although big conferences like the AGU Meeting feel impersonal, they always attract big names and you never run out of things to do in smaller groups and you can always meet people that work on similar topics like you. I feel privileged to have had the opportunity to listen to and meet some of the leading scientists and policymakers who see the big picture. As the AGU put it, “as scientists and engineers, we must continue to engage with policymakers, communities, businesses, and the public to undertake solution-oriented research and analysis. Scientific institutions, including academia and governmental agencies, should expand and prioritize their support for research, application, and knowledge dissemination to address the climate crisis.”
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