Measuring what people breathe in Athens over the last 10 months by using a portable sensor

Each square in the above graphic
represents one hour. The darker the color,
the higher the concentration (1hour average)
of PM 2.5 (red) or PM 10 (blue) according
to the Plume Air Quality Index.

Some of the news over the past few weeks that perhaps have not been given the attention they deserve, because of the Convid-19 pandemic, reflect the bitter reality of air pollution in our country. Just a few days ago, the European Commission referred Greece to the Court of Justice of the European Union over high limit values for PM10 concentrations (microparticles less than 10 micrometers in diameter) in the agglomeration of Thessaloniki for the last 14 years. Some weeks earlier, the European Environment Agency’s “Air Quality in Europe – 2020 Report” estimated that in 2018 there were 15.450 premature deaths in Greece from air pollution-related causes.

Map of Athens depicting atmospheric quality records (average) for the period of January – December 2020.

In January 2020, just before the outbreak of the pandemic, iMEdD Lab decided to measure the quality of air that an ordinary Athens’ citizen moving in the city breathes, by using a portable air quality sensor. To that end, Plume Labs sent us a portable sensor (model: Flow), which provides minute-by-minute measurements of concentrations of PM2.5, PM10, nitrogen dioxide (NO2), volatile organic compounds (VOCs), as well as the positional coordinates.

I – the author – living in the city center of Athens and mainly using a motorcycle as daily driver within a radius from Victoria square to Syntagma Square and places nearby, was wearing the sensor 24 hours a day during the period from January 14th 2020 to December 2nd 2020. The sensor made 400.862 measurements, sent at regular intervals to my cellphone, so that I would see the quality of air I was breathing in real time. The monitor’s manufacturer has developed an Air Quality Index (AQI), which takes into account the recommendations of the World Health Organization, as well as the particulate measurements made. For the visualization of data from the portable sensor, this index – divided into seven categories indicating increasing levels of health concern – was used. An AQI value of 0 – 20 represents good air quality; an AQI value of 21 – 50 represents a moderate level of concern, while an AQI value of 51 and higher (per 50 units up to 200) represents a high level of pollution.

The market of air quality monitoring systems (indoor, outdoor, portable) is rapidly expanding over the last few years, because of citizens’ awareness amongst other things of the consequences of air pollution on health and the environment. These monitors in no case substitute the official national air quality monitoring stations; however, they meet the need of those who wish to monitor the quality of the air they breathe, not just when they are out on the street, but also when they are at home. The sensor we used employs two different air quality measurement techniques: laser diffraction to count PM2,5 and PM10 particles and monitoring conductivity changes of metal oxides for NO2 and VOC.

“Small particle pollution has health impacts even at very low concentrations – indeed no threshold has been identified below which no damage to health is observed”

World Health Organization
feature image view from lycabettous hill
View of Athens from Lycabettous hill. ΑΠΕ-ΜΠΕ/ΑΠΕ-ΜΠΕ/Pantelis Saitas

Lockdown and its impact on air pollution

COVID-19 pandemic seems to have affected, even temporarily, air quality in Athens; a fact that was recorded in a study of the National Observatory of Athens published a few days ago but also confirmed by our measurements.

In fact, the Atmospheric Physics and Chemistry Group of the Institute for Environmental Research and Sustainable Development of the National Observatory of Athens, in cooperation with the University of Crete (Department of Chemistry) and the Paris – Saclay University, analyzed the changes in the levels of air pollutants during the first lockdown in Greece (March 23rd – May 10th, 2020), in relation to the periods before and after, based on data from the Observatory’s Air Pollution Monitoring Station in Thiseio. It is one of the few studies worldwide that analyzed the impact of lockdown on air quality and indeed revealed that during the 1st lockdown (March 23rd – May 10th, 2020), there was a 35% reduction in air pollution from vehicles (nitrogen dioxide – NO2, carbon monoxide – CO and fraction of black carbon – BC from fossil fuel combustion) in relation to the period from March 1st to March 22nd, 2020.

Our analysis was mainly focused on PM2.5 and PM10 airborne particulates. For classification, we used our sensor’s Air Quality Index. Indeed, it appears that during lockdown and in summer, the monthly mean PM2.5 and PM10 concentration was reduced; however this trend did not continue during the 2nd lockdown, where there was more road traffic.

Temporary improvement of air quality in Athens during the 1st lockdown

Data resulting from the measurement of the concentration of air pollutants using a portable monitor. Graph data values correspond to AQI values of the monitor used (Plume AQI).

What is PM 2.5 and PM 10

PM2.5 refers to particulate matter (PM) that has a diameter of less than 2.5 μm, while PM10 has a diameter of less than 10 μm. These particles pose the greatest health risk, because they are so small (especially PM2.5) that once inhaled, they can penetrate deeply into the lungs and bloodstreams, causing heart diseases, affecting blood vessels of the brain but also lungs, while they are considered by the International Agency for Research on Cancer (IARC) of the World Health Organization as the cause of lung cancer.

The higher the exposure of humans to PM2.5 and PM10 – exposure refers both to air pollutant concentrations and to the time of exposure in them-, the greater would be the risk of morbidity and mortality.

In accordance with the World Health Organization, exposure to PM2.5 and PM10 should not exceed the following levels:

PM 2.525 μg/m324-hour mean
10 μg/m3Annual mean
PM 1050 μg/m324-hour mean
20 μg/m3Annual mean
The daily mean of PM10 not to be exceeded more than 35 days a calendar year.

Analysis of the portable sensor’s data showed that the average concentration reported for a 10-month period was below WHO’s recommendations (8.2 μg/m3), and the pandemic played a key role in that. However, by calculating the hourly means based on Plume AQI, as shown in graph below, there have been several hours (1772 out of totally 6901) with moderate to very high air pollutant concentrations. Regarding PM10, the average concentration for the 10-month period is within the limits based on WHO’s safe thresholds (19.5 μg/m3).

Over the 301 days of measurements, 248 instances with PM2.5 values higher than 75 μg/m3 and 33 instances with PM2.5 values higher than 100 μg/m3 have been recorded. As regards PM10, 144 instances with values higher than 200 μg/m3 and 37 instances with values higher than 300 μg/m3 have been recorded.

The fact that these values are close to the maximum thresholds and taking into account that they have been recorded in the context of a pandemic, with two general lockdowns, teleworking and movement restrictions, indicates that under normal circumstances the exposure of an average person to air pollutants may exceed the maximum safe threshold set by WHO.

Analysis of fixed-site air pollution monitors in Sepolia and Ladadika – Thessaloniki.

A previous analysis of a fixed-site outdoor sensor in the city center of Athens (Athens Commercial Triangle) of Purple Air Ltd., which shares measurement data openly, had shown that the annual PM2.5 concentration for 2019 was 26.16 μg/m3; in other words, 2.6 times above the safe threshold of 10 μg/m3 recommended by WHO.

Athens (Sepolia) Monitor

  • <iframe src="" height="550" width="100%" allow="fullscreen"></iframe>
White areas represent missing data.

For the purpose of our analysis, data was mined from outdoor fixed-site sensors for two locations in Greece:  Sepolia and Ladadika in Thessaloniki. The following graphs reflect the daily means from July 2019 to November 2020. The darker the colour of each day, the higher the concentration of the pollutant selected from the dropdown menu would be.

Thessaloniki (Ladadika) Monitor

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White areas represent missing data.

At both locations, many days with increased concentrations of microparticles in the atmosphere have been recorded. Especially in Thessaloniki, values reach extremely dangerous to health levels. However, we need to bear in mind that this data does not substitute the official documented air pollution measurement data communicated by the authorities. Moreover, their records relate only to the specific sites where the monitors have been placed and not to the entire neighborhood or the entire city. This data though combined with the news reports on air quality in Greece, on premature deaths and on the country’s referral to the Court of Justice of the European Union over poor air quality in Thessaloniki, if anything, should give us pause for thought.

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