The local development and use of low-cost sensors is a means to make data collection more accessible to the Ethiopian scientific community, as well as offering practical experience to local staff.
A team of Arba Minch Water Technology Institute (AWTI) has assembled a soil moisture sensor system with arduino and micro-electronics. Last summer, I was able to bring five soil moisture capacitance sensors from The Netherlands. Demiso Daba, Tafesse Fitensa and Getachew Enssa followed the one-day Arduino workshop. A PhD student (Edmealem Temesgen) and MSc student (Chanako Dane) from the faculty of Irrigation became also involved, as the availability of measurement instruments makes it possible for them to collect primary data for their research.
Field installation
Field measurements
Soil moisture system inside
Soil moisture system outside
As part of his PhD study, Edmealem Temesgen conducts field comparisons between the sensor system and the laboratory volumetric method for soil moisture tests. The first results are very promising, see below figure.
Preliminary results of a comparison between volumetric method and sensor system soil moisture field measurements. Results currently under publication.
The Ethiopian Journal of Water Science and Technology (EJWST) has published an article by me and my students titled “Roadside PM2.5 concentrations measured with low-cost sensors and student science in Arba Minch, Ethiopia“. During April and May 2022, students of Water Supply and Environmental Engineering, year 3, conducted PM2.5 measurements at road-side locations. They did so with the locally assembled sensor system, as part of the course Air and Noise pollution. In this way, seven groups of 5-6 students collected approximately 2,500 hours of PM2.5 data. After the course, I analyzed the data and turned it into a manuscript. Two of the students (Mekdes Dawit and Tewodros Zerihun) provided valuable feedback and became co-authors to the article.
Students conducted measurements at six locations: four stationary and two mobile locations (Figure 1 in the article).
Measurements were conducted at six locations: one at the university campus gate, two at busy squares, one at the bus station, and two inside public transport tuktuks (bajaj). Except for the campus gate, at all locations concentrations exceeded WHO guideline values. Highest concentrations were observed during the morning period at the bus station. Supporting data and data processing code is shared on an OSF repository.
PM2.5 concentrations measured at six locations, in contrast with the WHO guideline (Figure 3 in the article).
Low-cost sensors and student science
The article is a showcase of the application of both locally assembled low-cost sensors and student science. Combined, these methods provided me with a lot of data for very little costs. At the same time it provided my students with practical experience as part of a course. During the course Air and Noise pollution, they got lectures on the course contents. They had to apply this knowledge by selecting a specific research question, constructing measurement plans, installing and operating the instruments, processing the data in Microsoft Excel, and writing a report.
One of the locally assembled low-cost particulate matter sensor systems.
The publication covers use of the sensor system across fourteen locations for more than 30,000 hours combined. In the publication, we openly share the system design. All data and materials supporting the publication are available in an OSF repository. We also show results of data quality validations. These validations included collocation of multiple sensors and gravimetric measurements.
It is not our intent to create and share the best sensor system. Rather, we want to show that a sensor system can be built locally, with two main benefits: lower costs and local experience training. Furthermore, we fill a gap in local validation of low-cost sensors. Several types of low-cost sensors are being used on the African continent. However, field validation under circumstances common to a country like Ethiopia are extremely limited. Up to my knowledge, we are the first to share validation of the Sensirion SPS30 with gravimetric measurements under high concentrations (inside kitchens with biomass fuel) and ambient concentrations in Ethiopia – or even Africa. Or, more correctly, we fill part of the gap. I want to add (much) more validation measurements. Some of this is ongoing. Currently, an MSc student compares my sensor systems with gravimetric measurements in Addis Ababa and Adama.
Lund university (Sweden), Haramaya University, Institutes of Geophysics, Space Science and Astronomy of Addis Ababa University, and the Department of Physics of North Carolina A&T State University co-organized the international conference ‘Together for cleaner air in Ethiopia’ (18-20 December 2023). I was offered the opportunity to give two presentations about the work at Arba Minch University: locally developing the low-cost sensor system, and conducting research with students (student science).
Participants of the ‘Together for cleaner air in Ethiopia’ workshop
Slides of the low-cost sensor system presentation:
Research budget in Ethiopia is extremely limited, and many of my colleagues are not involved in research due to that. The Water Resources Research Centre organized a seminar on conducting low-cost research at December 4, 2023. I presented from own experience on ‘How to collect +25,000 hours of data and create five scientific articles with almost no budget’. This included sharing my work on low-cost sensor development and conducting research with students. After presenting my experiences, we had an interactive session with the twenty attendants on what opportunities and challenges there are for low-cost research.
Wegene Negese, an MSc student at Arba Minch University (Climate) and employee of the Ethiopian Meteorology Institute (EMI), has conducted validation measurements of the low-cost sensor system with SPS30 Sensirion at the EMI meteorological stations of Addis Ababa and Adama. For a period of four months, he collocated the sensor system with itself, and conducted gravimetry measurements. Gravimetry is the reference method for calibrating PM2.5 measurement instruments.
Sensors were installed at meteorology stations of Addis Ababa and AdamaGravimetric analysis with filter measurements wasconducted to validate the sensor systems
He is currently working on his MSc thesis, but I can already present some preliminary results:
The coefficient of variation (CV; a measure of variation between two identical instruments) was 9.5% for two sensor systems in Addis Ababa (based on 12,677 10-minute averages), and 4.4% for two sensor systems in Adama (based on 4,135 10-minute averages). This indicates that the variation between two sensor systems is lower than 10%. 10% is set as a maximum allowed CV for measurement instruments by the NIOSH and the US EPA.
The sensor system systematically measures lower than gravimetry, but the correlation is strong. Linear regression of all data points of Addis Ababa and Adama combined (n=16) leads to a slope of 1.62 with an R2 of 0.99. The Pearson correlation is 0.97.
The data of Wegene confirms wat I found in earlier data with measurements in Arba Minch: the SPS30 Sensirion has low within-variation, and shows a stable bias both under ambient and indoor (high) concentration settings versus gravimetry measurements (see this publication). In other words: the SPS30 Sensirion appears to be a very good sensor under Ethiopian circumstances.
Together with my colleague Afework Tademe (electronics) I organized a one-day Arduino workshop, in order to help colleagues get started with building their own low-cost sensor systems. Five colleagues got a crash-course in microprocessors, sensors and electronics. As part of the program, participants built themselves working systems of relative humidity and temperature sensors, LEDs and real-time clocks. Hopefully we will see a variety of locally developed low-cost sensor systems!
Arduino class
Microelectronics
Arduino build
Background
Last June, I presented my work at the international symposium of my institute. That raised the question on whether the same principle (buying microelectronics and locally constructing sensor systems) could be used for the field of water- and soil studies. Over the summer I was able to bring to Ethiopia cheap soil moisture, water level and water temperature sensors. The one-day Arduino workshop on building sensor systems is meant to motivate colleagues to start building their own low-cost instruments.
Below you can see the slides used during the workshop.
I presented my work on low-cost research methods at the 21st International Symposium on Sustainable Water Resources Development (June 9-10, 2023). This symposium is organized by my institute (Arba Minch Water Technology Institute) and the Water Resources Research Center (WRRC).
Arba Minch University faced budget cuts, which reduces opportunities for local staff to conduct research. Reducing research costs expands research opportunities at this time, because many staff members are idle. Therefore, my focus on low cost research by using Do-It-Yourself (DIY) measurement setups and students as data collectors (student science) caught the attention of the research director of the WRRC. He invited me to present about these two cost-saving methods on the symposium. See here the slides of the presentation.
Apart from presenting, I could display different instruments on tables. I showed all components that go into the low-cost PM2.5 sensor system. Participants could try to register the highest CO2 concentration by blowing into an CO2 measurement instrument. Also, the recently launched awtiCode was on display, and participants could leave suggestions and questions for Python code.
Across various locations I have used the IQAir Airvisual Pro (IQAV), the UCB-PATS+ (PATS), and the Sensirion SPS30 as part of a locally assembled sensor system (SPSA). I have analyzed the data of different locations where those low-cost sensors (LCS) were collocated. At some of those locations, I also conducted gravimetry measurements with the UPAS. Based on this, I conducted an evaluation of the low-cost sensors PM2.5 data quality in three ways:
Within identical sensors (how do identical sensors compare to each other);
With each other (how do the measurements of one LCS compare to another LCS);
With the reference method (gravimetry is the golden standard for PM2.5 measurements).
My primary interest is the data quality of the SPSA. The IQAV and PATS cost about 300-500 euros. We construct the SPSA locally, and it costs about 60 euros. I found out that both under ambient and indoor (high and highly variable concentrations) circumstances, the SPSA data quality is equal to if not better than that of the IQAV and the PATS. More importantly, based on the data collected so far, the SPSA data quality compares well to international data quality requirements. The coefficient of variation (a measure of variation between identical sensors) ranged between 3 and 7% across low and high concentrations. This is lower than the required 10%. The accuracy versus gravimetric samples (a measure of how much it is ‘off’) was 16% under ambient and 15% under indoor circumstances. This is lower than the required 25%.
I will continue collecting data with the SPSA. For example, the gravimetry comparison under ambient conditions was only based on three samples. However, so far it is very promising that with a locally assembled sensor system we can surpass data quality of commercially available instruments and reach international standards.
Concentration levels
The analysis included data from several measurements, across low (<10 μg/m3) to high (>10,000 μg/m3) concentrations. Below, concentrations of all LCS across various locations are shown (Figures A1 and A2 of the article).
