Author: Julien Anet

Low-power method for accurate environmental temperature measurements

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. 

The complete bachelor thesis can be found here

Developing mobile RHT-Sensors for urban heat island detection using public rental bikes

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.

Deployment of a new LDSA-sensor network

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.

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)

COVID-19: A unique air quality study?

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.

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.

Stay tuned!

Group retreat

365 days happen to pass extremely quickly, especially during the buzzing university terms. Yet, regular discussions, making sure our plans still fit the main mission to provide significant services to the global community, are of uttermost importance.

A yearly group retreat allows us to take some distance from the everyday rush, changing the perspective and therefore helping the development of new ideas and projects.

This year, we decided to do our group retreat in the premises of “museum schaffen.” Located in the former buildings of the “Schweizerische Lokomotiv- und Maschinenfabrik” (SLM), “museum schaffen” recently opened a work lab with all kinds of tools, creating an inspiring and empowering atmosphere for a retreat.

We set out to define our visions for the next 12 – 24 months in scientific projects, services and teaching. While identifying our own strengths and weaknesses, we started by getting to know each other better and ended with generating a clear plan for the next two years. For teaching, this involved the identification of potential topics for Bachelor- and Master theses. For scientific projects and services, we focused on parallel activities in the field of weather, climate & environmental protection including aviation emissions, on mutual coaching activities and on potential publications to be tackled soon.

Because intense brainwork needs some physical activity as compensation, the afternoon was spent in the climbing hall “6a+“. While Jazz & Lukas got a professional introduction by Damaris, our climbing teacher, Curdin & Julien got a serious brush-up on indoor climbing technique. We all ended up having sore forearms and cramped toes, but filled with endorphins and ready to conquer the next 365 days of work!

Visit of MeteoSwiss HQ with our students

Each year, I am teaching around 60-80 students some meteorological basics. The courses include a wrap-up of first year physics, and builds upon this knowledge to introduce some applied notions of thermodynamics and fluid dynamics (see course description here).

The main aim of the course is to enable students to understand, categorize and maybe even generate own weather forecasts, with a special focus on the most important hazardous weather phenomena both for commerical and general aviation.

Thanks to the very fruitful collaboration with MeteoSwiss, interested students have always been able to join a guided tour through the MeteoSwiss Headquarters at the airport of Zurich.

The tour mostly begins with a short welcome note on the observation deck, before boarding a passenger bus leading to the threashold of runway 16. There, the tour guide shows and explains the different meteorological instruments partly used for the meteorological report (METAR). The group is then lead to the meteorological observation platform. There, the duty of an “aeronautical meteorological observer” (see here for a definition) is introduced to the students.

Group of students walking up the stairs to the weather observation tower

Finally, the forecasting front office is shown, were one of the two on-duty forecasters answer the – mostly numerous – questions of the students.

Once again, it was a very interesting guided tour, and all our students were extremely happy to have been able to take part.

Many thanks to Peter Meyer, Martin Dätwyler, Thomas Jordi, Andreas Asch and the remaining team of MeteoSwiss to make this yearly tour possible!

METENVIA – and our mission

We are a team of highly motivated atmospheric and environmental scientists. We are especially curious about aircraft engine emissions and how they impact local air quality. In addition, we look for new ways to improve the awareness of aviation professionals towards meteorological effects on aviation, environmental protection, and global climate change.

From left: C. Spirig, L. Durdina, J. Anet, J. Edebeli, S. Fluck

We pursue mainly three goals:

First, we aim to generate new scientific knowledge, e.g. about the toxicity and the environmental burden of aircraft engine emissions. We are convinced that passenger aircraft will rely on gas turbine engines throughout the next decades. Therefore with our measurement data, we analyze different possible elements impacting emission characteristics, such as environmental factors, fuel composition, engine technology and engine age. Aircraft emissions and their impact on regional air quality within the boundary layer and on the ground are still poorly understood despite many years of work. Thus, through modeling studies, we aim to visualize and quantify aviation effect on the chemical composition of the air.

Second, meteorological factors regularly impact air transport frequently leading to delays, often to incidents, and sometimes to accidents. Our vision is to improve the awareness of aviation staff towards weather-related factors by focusing on easy-to-understand teaching methods, and simulation and visualization of meteorological processes. As well, we support knowledge transfer within the meteorological community as much as possible.

Finally, we act as consultants whenever know-how generation about environmental protection or climate change is required. This includes, among others, modelling studies or redaction support.

We are driven by the urgent need to address global climate change and environmental protection by paradigm shifts within all branches of mobility.

Hello World!

It’s happening – METENVIA, the research unit “Meteorology, Environment and Aviation” of the Centre for Aviation from ZHAW just came alive!

In the forthcoming weeks and months, we will tackle mostly aviation-related ongoing environmental and meteorological challenges. Yet, our competencies don’t stop there; we will contribute to other projects fitting to our mission statement. Stay tuned to get to know more about the latter!

Bildergebnis für hello world"