Urban Air Quality in a Residential Building in Athens, Greece

Proceeding Paper Urban Air Quality in a Residential Building in Athens, Greece † Marita-Louiza Nikolakou * and George Spyropoulos Laboratory of Soft Energy Applications & Environmental Protection, Mechanical Engineering Department, University of West Attica, 250 Thivon and P. Ralli Str., GR-12244 Athens, Greece; [email protected] * Correspondence: [email protected] † Presented at the 16th International Conference on Meteorology, Climatology and Atmospheric Physics—COMECAP 2023, Athens, Greece, 25–29 September 2023. Abstract: Being comfortable and healthy in one’s home is of the utmost importance and a contributing factor to the quality of their life, and it is greatly affected by the air quality of the residence. Therefore, the subject of this paper centres around the indoor air quality (IAQ) of a standard household in central Athens and how these components influence human health. The air quality assessment is conducted using particulate matter (PM) on-site continuous measurements taken from low-cost sensors (PurpleAir) installed both inside and outside the house. Focusing especially on PM2.5 data from September 2021 to September 2022, the Air Quality Index (AQI) and the number of exceedances are evaluated in detail, investigating the association between indoor and outdoor environments. Keywords: air quality; indoor air quality; air pollution measurements; PurpleAir; low-cost sensors; IAQ; AQI; Athens 1. Introduction Citation: Nikolakou, M.-L.; Spyropoulos, G. Urban Air Quality in a Residential Building in Athens, Greece. Environ. Sci. Proc. 2023, 26, 153. https://doi.org/10.3390/ environsciproc2023026153 Academic Editors: Konstantinos Moustris and Panagiotis Nastos Published: 1 September 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Maintaining IAQ is vital for people’s well-being and comfort. It can be affected by several factors, including the rate of ventilation, air distribution patterns, and pollution sources. To achieve acceptable IAQ, the World Health Organization (WHO) has recommended a list of pollutants [1]; however, this paper will focus on only one pollutant from the list, PM2.5 . While there has been increasing concern about the impact of atmospheric PM on human health, resulting in stricter regulations for controlling ambient air quality, similar awareness for indoor environments has not been achieved [2–5]. This is alarming, considering that people, especially in urban areas, spend more than 80% of their time indoors in homes, offices, schools, transportation, and other gathering places [6]. Furthermore, several studies have shown that air pollution can be the cause of asthma, respiratory disease, chronic bronchitis and even heart disease [7–9]. The rising concern for the health effects of air pollution has led to the development of low-cost sensors that can be used in residential environments to monitor the IAQ of one’s home. PurpleAir is a community-based system that utilizes low-cost sensors to measure PM of different sizes, including PM1.0 , PM2.5 and PM10 . The PurpleAir system relies on a decentralized approach, where community members take responsibility for installing, operating, and maintaining the sensors. This distributed model facilitates a broader coverage of monitoring locations and engages local communities in actively contributing to air quality data collection [9–11]. It should be noted that the measurements of PurpleAir sensors cannot be used for assessing ambient concentration levels as they may have limitations and may not provide entirely accurate results for evaluating regulatory compliance with air quality standards. However, after undergoing calibration they can be utilized to offer realistic ambient concentration levels [7,12,13]. This paper assesses the air pollution levels of a residence located in central Athens using data from PurpleAir’s low-cost sensors. For this reason, the AQI was calculated. The results highlight the need for the development of combined strategies and for enabling occupants to use ventilation systems aiming to achieve optimum air quality. Environ. Sci. Proc. 2023, 26, 153. https://doi.org/10.3390/environsciproc2023026153 https://www.mdpi.com/journal/environsciproc Environ. Sci. Proc. 2023, 26, 153 Environ. Sci. Proc. 2023, 26, 153 2 of 6 This paper assesses the air pollution levels of a residence located in central Athens using data from PurpleAir’s low-cost sensors. For this reason, the AQI was calculated. The results highlight the need for the development of combined strategies and for enabling occupants to use ventilation systems aiming to achieve optimum air quality. 2 of 6 2. Area of of Study 2. Area Study TheThe residential study,asas seen in Figure is located in central residentialbuilding building under under study, seen in Figure 1, is 1, located in central Athens Athens approximately 1.5km kmfrom from Metaxourgio, Metaxourgio, 3.53.5 kmkm from Syntagma, 850 m850 from parkthe park approximately 1.5 from Syntagma, mthe from Academy of Plato and near two avenues. The climate is Mediterranean, with mild, modAcademy of Plato and near two avenues. The climate is Mediterranean, with mild, moderately rainy wintersand andhot, hot, sunny sunny summers. Summers in Athens are characterized by erately rainy winters summers. Summers in Athens are characterized by hot, dry, and clear weather conditions, whereas winters tend to be long, cold, windy, and hot, dry, and clear weather conditions, whereas winters tend to be long, cold, windy, and partly cloudy. The hot season spans approximately three months, starting from 10 June partly cloudy. The hot season spans approximately three months, starting from 10 June and and ending on September 12 with an average daily high temperature that exceeds 29.4 °C. ◦ ending 12 with an average daily high temperature exceeds2429.4 The on coolSeptember season extends for approximately four months, starting fromthat November and C. The coolending seasonon extends forwith approximately fourhigh months, startingthat from November 24 and 27 March an average daily temperature remains below 16.7 °C ending on 27 March with an average daily high temperature that remains below 16.7 ◦ C [14]. [14]. Figure 1. The area of study (source Google Maps). Figure 1. The area of study (source Google Maps). 3. Materials and Methods 3. Materials and Methods 3.1. Instrumentention 3.1. Instrumentention The monitoring of the residence was executed with the help of two PurpleAir Classic The monitoring of(PA-II). the residence wasaexecuted with the help of twoand PurpleAir Air Quality Monitors To facilitate comparison between the indoor outdoor Classic Air Quality Monitors (PA-II). facilitate a comparison the indoor environment, one sensor wasTo installed inside the residence between and one outside on theand bal-outdoor environment, sensor was inside the residence and one system outsidethat onfacilthe balcony. cony. They one are equipped withinstalled an electronic two-channel data recording itates collectionwith of data can latertwo-channel be uploaded todata the cloud or stored in an SD card. They are the equipped anthat electronic recording system that facilitates By means ofofdual laser counters (PMS-5003), the sensors PM concentrations the collection data that can later be uploaded to themonitor cloud the or stored in an SD card. By in real The PM measurements then utilisedmonitor in the estimation the PM1.0, means of time dual[11,15]. laser counters (PMS-5003),are the sensors the PMofconcentrations in PM2.5 and PM10 concentrations, and two data series are generated (CF1 and ATM) [16]. In real time [11,15]. The PM measurements are then utilised in the estimation of the PM1.0 , this study, all the calculations were performed with the use of the CF1 data. PM2.5 and PM10 concentrations, and two data series are generated (CF1 and ATM) [16]. In this 3.2. study, the calculations were performed with the use of the CF1 data. Dataall Calibration As mentioned in the Introduction section, before any calculations are a empted, the measurements should be calibrated. Various studies have found significant correlations As mentioned in the Section 1, before calculations aremonitors, attempted, the measurebetween the measurements of Plantower PMSany sensors and reference indicating 3.2. Data Calibration ments should be calibrated. Various studies have found significant correlations between the measurements of Plantower PMS sensors and reference monitors, indicating their capability to provide reliable data as well as also identified biases associated with relative humidity and elevated levels of ambient PM [12,13,17–20]. As a result, different approaches were proposed in order to address and correct the concentration outputs of the sensors. The data of the current study are from September 2021 to September 2022 and have been calibrated using the following equation [12]. PM2.5cor = 0.000387 × PM2.5(CF=1) 2 + 0.443 × PM2.5(CF=1) + 2.6 (1) where PM2.5(CF=1) is the average of the PM2.5(CF=1) measurements from the two data series. Environ. Sci. Proc. 2023, 26, 153 3 of 6 3.3. Air Quility Index Calculation • The AQI calculation was based on the following equation [21]: AQI = AQIHi − AQILo × (Conci − ConcLo ) + AQILo ConcHi − ConcLo (2) where Conci is the input concentration for a given pollutant, in this case PM2.5 , ConcLo is the concentration breakpoint that is less that or equal to Conci , ConcHi is the concentration breakpoint that is greater than or equal to Conci , AQILo is the AQI value/breakpoint corresponding to ConcLo , and AQIHi is the AQI value/breakpoint corresponding to the ConcHi . The numbers used for the calculations are presented in Table 1. Table 1. AQI and concentration breakpoints for PM2.5 . PM2.5 ConcLo (µg/m3 ) ConcHi (µg/m3 ) AQILo AQIHi Good Moderate Unhealthy for Sensitive Groups Unhealthy Very Unhealthy Hazardous 0.0 12.1 35.5 55.5 150.5 250.5 12.0 35.4 55.4 150.4 250.4 500.4 0 51 101 151 201 301 50 100 150 200 300 500 4. Results The number AQI exudences and their percentage in the data set are presented in Table 2. It is evident that even though the residence is in an urban area and near two avenues, the air quality for the most part is within the boundaries of “Good” and “Moderate”. Notably, the difference between indoors and outdoors is minimal but not nonexistent. There is a 1.9% difference in the “Unhealthy for Sensitive Groups” category and a 2.4% difference in the “Unhealthy” category as well as the appearance of “Very Unhealthy” and “Hazardous” outdoors. Another important contrast is the appearance of more “Moderate” values indoors rather than outdoors, representing a difference of 5.2%. This is also apparent in Figure 2a, though further elaboration on this matter will be provided in the following section. The differences might be minute, but it is apparent that the air quality is better indoors. Table 2. The number of AQI exudences and their percentage in the data set. Good Moderate Unhealthy for Sensitive Groups Unhealthy Very Unhealthy Hazardous AQI Indoor Indoor (%) Outdoor Outdoor (%) 0–50 51–100 101–150 151–200 201–300 ≥301 5059 4055 184 77 0 0 54.0% 43.3% 2.0% 0.8% 0% 0% 5101 3576 361 297 35 5 54.4% 38.1% 3.9% 3.2% 0.4% 0.1% The monthly, daily and hourly average of the AQI for PM2.5 is depicted in Figure 2a–c, accordingly. For the monthly average, one can observe that the average outdoor AQI is higher than the indoor one during autumn and winter, but the opposite is true for two out of the three spring months as well as during the summer. The paradox occurring during the hot months can be attributed to the air conditioning and the poor ventilation of the residence due to the high temperatures that prevent the home owners from opening the windows. Regarding the winter months, it is evident that the average outdoor AQI is significantly higher than indoors. The cause of this is the smoke that pollutes the atmosphere from the use of fireplaces. The notable disparity observed in March could potentially be caused by an increase in pollen levels. Environ. Sci. Proc. 2023, 26, 153 average is higher than the outdoor average around the time people commence their daily activities. The ambient atmosphere is disrupted, as activity resumes within the house. When the occupants of the residence leave for work, the house remains closed, resulting in the indoor pollution levels remaining elevated until the typical end of the workday. Regarding the evening and night hours, as stated before, the occupants return and venti4 of 6 late the house. Subsequently, activities gradually diminish as the day comes to an end, and the occupants go to sleep. Environ. Sci. Proc. 2023, 26, 153 5 of 6 Figure 2. 2. (a) (a) The The monthly monthly average average of of the the AQI AQI for for PM PM2.5 for indoor and outdoor and the boundaries Figure 2.5 for indoor and outdoor and the boundaries of “Good” and “Moderate”; (b) The daily average of the AQI for PM2.5 for indoor and outdoor and of “Good” and “Moderate”; (b) The daily average of the AQI for PM2.5 for indoor and outdoor and the boundaries of “Good” and “Moderate”; (c) The hourly average of the AQI for PM2.5 for indoor the boundaries of “Good” and “Moderate”; (c) The hourly average of the AQI for PM2.5 for indoor and outdoor and the parts of the day [22]. and outdoor and the parts of the day [22]. 5. Conclusions In terms of the daily average, there is no day when the indoor average exceeds the outdoor However, is an increase inPM both and outdoor Theaverage. Air Quality Index there was calculated with 2.5 indoor measurements frommeasurements low-cost Purduring the weekend. To draw accurate conclusions, simultaneous recordings would be pleAir sensors for an urban residence in central Athens. The data covered the time span necessary to account whether someone is atsignificantly home or not. It is possible that values the owners from September 2021for to September 2022. The higher indoor AQI durof are home in the weekends andofthat might generally be ingthe theresidence hot months of themore yearhours and the morning hours thethere day emphasize the immore traffic the area.comprehensive strategies and enabling occupants to utilize portance of around implementing With respect hourly it isairnoteworthy to highlight the differences ventilation systemstointhe order to a average, ain optimal quality. Subsequent research will incorobserved between indoors and outdoors in the morning and afternoon, as well as in the porate the significance of thermal comfort in conjunction with IAQ. evening and early hours of the night. For the morning hours, one can see that the indoor Lastly, it should be mentioned that low-cost air pollution sensors have become inaverage is higher than the outdoor average around the time people commence their daily creasingly valuable for real-time and localized air quality monitoring. In the past, governactivities. The relied ambient is disrupted, as activitytoresumes the house. ment agencies on atmosphere expensive and intricate equipment conduct within air quality moniWhen occupants of the data residence leave for remains resulting toring,the resulting in limited availability for work, only athe fewhouse selected areas.closed, Fortunately, the in the indoor pollution levels remaining elevated until the typical end of the workday. advent of low-cost sensors has revolutionized the field, offering affordable and userRegarding the evening and night hours, as stated before, the occupants return and friendly solutions for monitoring air quality. These sensors have broadened the ventilate scope of the house. Subsequently, activities gradually diminish as the day comes to an end, and the monitoring by making it possible to assess air quality in numerous locations at a reduced occupants go to sleep. cost. 5. Conclusions Author Contributions: Conceptualization, G.S.; methodology, M.-L.N., G.S.; formal analysis, M.Quality Index was calculated with measurements low-cost PurL.N., The G.S.;Air investigation, M.-L.N., G.S.; resources, G.S.;PM data M.-L.N.,from G.S.; writing—origi2.5curation, pleAir for anM.-L.N.; urban residence in central Athens.M.-L.N., The data covered the time span nal draftsensors preparation, writing—review and editing, G.S.; visualization, M.-L.N., G.S.; supervision, G.S. All authors have2022. read The and agreed to the published version of the manuscript. from September 2021 to September significantly higher indoor AQI values during the hot months of thereceived year and morning hours of the day emphasize the importance Funding: This research nothe external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Environ. Sci. Proc. 2023, 26, 153 5 of 6 of implementing comprehensive strategies and enabling occupants to utilize ventilation systems in order to attain optimal air quality. Subsequent research will incorporate the significance of thermal comfort in conjunction with IAQ. Lastly, it should be mentioned that low-cost air pollution sensors have become increasingly valuable for real-time and localized air quality monitoring. In the past, government agencies relied on expensive and intricate equipment to conduct air quality monitoring, resulting in limited data availability for only a few selected areas. Fortunately, the advent of low-cost sensors has revolutionized the field, offering affordable and user-friendly solutions for monitoring air quality. These sensors have broadened the scope of monitoring by making it possible to assess air quality in numerous locations at a reduced cost. Author Contributions: Conceptualization, G.S.; methodology, M.-L.N. and G.S.; formal analysis, M.-L.N. and G.S.; investigation, M.-L.N. and G.S.; resources, G.S.; data curation, M.-L.N. and G.S.; writing—original draft preparation, M.-L.N.; writing—review and editing, M.-L.N. and G.S.; visualization, M.-L.N. and G.S.; supervision, G.S. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. 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