How Students Are Getting Involved — Air Quality in Milton, Ontario
Preface by: Kieran Berryman
What would you do if you thought your air quality might be poor? This group of students in Milton, Ontario, decided to take matters into their own hands. They deployed PurpleAir sensors in the North and South of Milton and collected data over a period of approximately one month. With the data now in hand, they hope to leverage it in a positive way.
This article was authored by: Jenay Khatri, Ritvik Manicka, and Suraj Subrahmanyan.
Introduction
Particulate matter (PM), including PM2.5, represents a risk to human health at elevated levels. Li et al. suggest common sources of PM concentrations are smoking, cooking, fuel combustion for heating, human activities, and burning incense (Li et al., 2017). Though studies looking at indoor PM concentrations have been extensively performed in various countries in Asia where PM concentrations are much higher compared to North America, such investigations, at least in the literature, have yet to include cities in Canada. As such, given Canada’s target of welcoming 500,000 immigrants on an annual basis (Immigration, 2024), this increase in population will undoubtedly lead to greater demand for housing and infrastructure, leading to higher indoor PM2.5. Therefore, looking at indoor PM levels in Canadian cities, particularly in rapidly growing areas, is crucial for developing effective public health strategies. Hence, to understand this in a growing GTHA (Greater Toronto Hamilton Area) suburb, Milton was chosen as the location for the study as the city represents one of the fastest-growing cities in all of Ontario (Government of Canada, 2022). In the study, we used purple air sensors from PurpleAir which has been shown in studies to accurately capture data at 99% accuracy of industry-standard PM monitoring stations. The sensors from PurpleAir were used as indoor air quality sensors, and to best capture the range of PM values in the households, the sensors were placed inside family homes at the two locations: The North end and the South end of Milton.
Data Collection
We collected data from April 28, 2024, to May 23, 2024. PM Concentrations were collected using sensors provided by the company, PurpleAir which is situated in Utah. These sensors were placed at both locations and recorded data every minute. The PurpleAir app transmitted raw data of multiple PM Concentrations and other measures in real time. This data was then exported to Microsoft Excel to model the data, visualize the trends, and perform preliminary analyses.
Results
World Health Organization (WHO) has made specific guidelines suggesting PM levels that should not be exceeded. According to WHO, the guidelines are as follows: 100 μg/m3 for 15 minutes and 35 μg/m3 for 1 hour; 10 μg/m3 for 8 hours; and 7 μg/m3 for 24 hours (World Health Organization, 2010).
Figure 1
Indoor PM2.5 Average Concentrations vs. Day in Month
Note. The graph shows indoor PM2.5 24-hour average concentration during April and May.
Figure 1 displays the average indoor PM2.5 concentrations over several days for two regions in Milton: the south (represented by orange squares) and the north (represented by blue diamonds). In the southern region, a significant spike in PM2.5 concentration is observed on April 29, 2024, where levels reach approximately 37 µg/m³. Following this, during early May (from May 2 to May 9), the concentrations drop significantly, stabilizing below 10 µg/m³, with most values around 5 µg/m³. However, from May 10 to May 19, a noticeable upward trend emerges, with concentrations gradually increasing, reaching peaks of around 15 µg/m³ and higher on certain days, which poses a risk to the health of individuals as stated by the WHO guidelines. In the northern region, PM2.5 levels remain relatively stable and lower compared to the south throughout the entire period, with most values staying below 10 µg/m³. Even during the mid-May period (from May 10 to May 19), there is only a slight increase in concentrations, with values peaking at around 10 µg/m³. Overall, the southern region consistently shows higher indoor PM2.5 concentrations than the northern region. This pattern is particularly pronounced on specific dates, such as April 29, 2024, and during mid-May 2024, when the south experiences significant spikes in PM2.5 levels. The sharp increase in PM2.5 levels in the south on April 29 may indicate an event or specific activity that led to a temporary but substantial rise in indoor particulate matter. The mid-May increase observed in both regions suggests potential seasonal factors, changes in ventilation patterns, or other environmental influences affecting indoor air quality. This analysis highlights that indoor air quality, particularly in the south of Milton, can vary significantly depending on specific days, potentially influenced by outdoor conditions or specific indoor activities.
Figure 2
PM Average Concentration vs. Time
Note. This graph shows the PM Average Concentration in a day.
Figure 2 compares the average PM2.5 concentration in the south and north of Milton, Ontario, over a 24-hour period. In South Milton (represented by blue diamonds), the PM2.5 levels are relatively low during the morning hours (0-6 hours), mostly staying below 5 µg/m³. As the day progresses into midday (6-15 hours), there is a slight increase in PM2.5 levels, but they remain relatively stable, hovering around 5-10 µg/m³. However, during the late afternoon to evening hours (15-24 hours), a significant spike in PM2.5 levels is observed, peaking at around 20 µg/m³, indicating higher particulate matter during these hours. In North Milton (represented by green triangles), the PM2.5 levels during the morning hours (0-6 hours) are similarly low, mostly under 5 µg/m³. As the day moves into midday (6-15 hours), a steady increase in PM2.5 levels is observed, but the concentrations remain lower compared to South Milton, staying mostly under 10 µg/m³. During the late afternoon to evening hours (15-24 hours), PM2.5 levels in the north show a slight increase, peaking at just over 10 µg/m³, but they remain lower than those observed in South Milton. Overall, the PM2.5 levels in the south are consistently higher than in the north, especially during the late afternoon and evening hours. This suggests that the southern part of Milton may experience more pollution later in the day, potentially due to factors such as traffic, industrial activity, or other sources of particulate matter. The highest concentrations of PM2.5 in both regions occur between 15 and 20 hours, with the south showing a more pronounced increase. This analysis indicates that certain activities in the south of Milton may contribute more to air pollution during the later hours of the day.
Conclusions
Ultimately, our study helps highlight the periods in time when indoor PM2.5 levels reach their peak and their potential for dangerous levels of exposure. In the case of the study, the period between 4-6 pm often resulted in the highest PM2.5 levels in the day. We attributed this feature to the resultant emissions from cooking dinner in the evening. Furthermore, we noted, at least in the surveyed houses, indoor PM2.5 rarely exceeds WHO standards to pose a significant health risk. Ultimately, the study has provided a clearer snapshot of PM2.5 levels in houses in the Milton area.
References
Government of Canada, S. C. (2022). Canada’s fastest growing and decreasing municipalities from 2016 to 2021. Www12.Statcan.gc.ca. https://www12.statcan.gc.ca/census-recensement/2021/as-sa/98-200-x/2021001/98-200-x2021001-eng.cfm
Immigration, R. and C. C. (2024). CIMM – Immigration Levels Plan for 2024-2026 – November 07, 2023. Www.canada.ca. https://www.canada.ca/en/immigration-refugees-citizenship/corporate/transparency/committees/cimm-nov-07-2023/immigration-levels-plan-2024-2026.html
Li, Z., Wen, Q., & Zhang, R. (2017). Sources, health effects and control strategies of indoor fine particulate matter (PM2.5): A review. Science of the Total Environment, 586, 610–622. https://doi.org/10.1016/j.scitotenv.2017.02.029
World Health Organization. (2010). WHO guidelines for indoor air quality: selected pollutants. Who.