The presentation gives an investigation on air quality monitoring in Stellenbosch using the Low-Cost Purple Air sensor. It investigates the possible emission sources and the potential effects of particulate matter 2.5 on human health.
1. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Compiled by: Kereemang Gaoaaga Supervisor: Dr Susanne Fietz
A Call to Action for Air Quality Monitoring in
Stellenbosch: Potential for Low-Cost Sensor
in Air Quality Research
2. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Figure 1; Adapted from IQAir, 2021 World Air Quality Report
2021 Global Air Quality Map for PM2.5
Population
weighted,
2021
average
PM2.5
concentration
(μg/m³)
for
countries,
regions,
and
territories
in
descending
order
Problem Statement
Stellenbosch is facing estimation of the population health risks of PM2.5 due
to insufficient PM2.5 data, as a result of lack of air quality monitoring.
3. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
What is PM2.5
Where does PM2.5 come from?
Effects of PM2.5 on human Health?
How to measure PM2.5?
How to Protect Ourselves?
Background
Images courtesy of U.S. EPA
https://sites.google.com/site/pm25inbeijing/
Outdoor
• Vehicle Emission
• Power plants
Indoor
• Cooking & Heating
• Cigarettes burning
Short-term Effects
• Headache
• Aggravated asthma and TB
Long-term Effects
• Non-fatal heart attack
• Decreased lung function
• Super tiny solids/liquids with diameter of 2.5 microns and below that are
suspended as atmospheric aerosols
• Air quality monitoring -Ground-based stations/ Low-cost sensors
• Conduct researches to monitor and avail data to the scientific air quality community
• The Low-cost sensors can be used to fill these gaps in air quality research
4. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
To collect ambient air data in Stellenbosch
using the PA-II-SD Air quality sensor
To determine PM2.5 air pollution sources
and investigate on health assessment
relative to South African air quality limits
and WHO air quality guidelines.
Assess relationship between PM2.5 measure
in Stellenbosch and meteorology
Objectives
To monitor real-time outdoor PM2.5 air
quality in Stellenbosch, and assess if it
affects human health in the Town
Aim
5. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
• Study period -July to September
• Air data was collected using the PA-II-SD
sensor at an hourly resolution
• Installed in my backyard- Cloesteville.
• Weekly check into the Purple Air map to
observe the peak frequencies and pattern
Methods
www.purpleair.com
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Results and Discussion
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35
PM2.5
Concentration
(µg/m3)
Time (Days)
PM2.5 Concentration For Month of July
18
WHO
SA NAAQS
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35
PM2.5
Concentration
(µg/m3)
Time (Days)
PM2.5 Concentration For Month of August
15
7
12
17
22
27
32
37
0 5 10 15 20 25 30 35
PM2.5
Concentrations
(µg/m3)
Time (Days)
PM2.5 Concentration In Month of September
12
• Mean PM2.5 >> 18µg/m3
• Highest peak >> 33 µg/m3
• Lowest peak >>10 µg/m3
• Solid fuel
• Mean PM2.5 >>15 µg/m3
• High peak >>25 µg/m3
• Lowest peak >>7 µg/m3
• Mean PM2.5 >>12 µg/m3
• Highest peak >>20 µg/m3
• Lowest >>9 µg/m3
WHO
SA NAAQS
WHO
SA NAAQS
PM2.5 Measured in Jul, Aug & Sept
7. 0
20
40
60
80
100
120
0 5 10 15 20 25
PM2.5
Concentration
(µg/m3)
Time (Hours)
Time-series plot of PM2.5 Concentration measured in
July (80/07/22)
4
5
6
7
8
9
10
11
0 5 10 15 20 25
PM2.5
Concentration
(µg/m3)
Time (Hours)
Time-series plot of PM2.5 Concentration measured in
August (30/08/22)
• Morning peaks were less vivid
• Noon (12:00-14:00) and evening peak (17:00 -19:00)
are more prominent
• Therefore I suggests that the source of PM2.5 is
associated with vehicle emissions (traffic peak hours)
Potential Sources of PM2.5 in Stellenbosch
8. PM2.5 variation on Weekdays and weekends
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0 200 400 600 800 1000 1200 1400 1600
PM2.5
Concentration
(µg/m
3
)
Time (hrs)
PM2.5 measured on Weekdays
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0 100 200 300 400 500 600 700
PM2.5
Concentration(µg/m
3
)
Time (hrs)
PM2.5 measured on Weekends
0 10:00 14:00 15:00 16:00 17:00 18:00 19:00
0 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00
• The mean PM2.5 >> 15 µg/m3
• Weekdays recorded high PM2.5 >> 104 µg/m3
• Weekends PM2.5 >> 82 µg/m3
9. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Potential Sources of PM2.5 in Stellenbosch
Adapted from the HYSPLIT model online by the NOAA
10. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
PM2.5
Concentration
(µg/m3)
Time (Days)
July Aug Sept
Stellenbosch Station Cape Town Station
4
6
8
10
12
14
16
0 5 10 15 20 25 30 35
PM
2.5
Concentration
(µg/m3)
Time (Days)
July Aug Sept
15 8
Spatial Comparison between the stations
• Stellenbosch recorded high PM2.5 compared to Cape Town
11. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Correlations of PM2.5 Concentration with
Meteorological Parameters
Positive Correlation with PM2.5
Humidity
Negative Correlation with PM2.5
Temperature
No correlation
Wind Speed
Rainfall
Correlation
Study Period
PM2.5 Vs
Temperature
PM2.5 Vs
Humidity
PM2.5 Vs
Wind Speed
PM2.5 Vs
Rainfall
Linear
Analysis (R2)
0.04 0.06 0.04 0.04
Spearman
Analysis (R)
-0.23 0.31 -0.04 -0.07
P-Value P<0.001 P>0.1
P>0.3
P<0.001
12. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Air Data collected by the
Purple Air Sensor (PAS)
Air Data collected by the
ground-based monitors
Depicts data from the Cape Town Municipality Achieves
Depicts
data
downloaded
from
the
PA
cloud
13. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Cost more than US $100,000 ~ over
R1.7M (Maag et al., 2018; Rai et al.,
2017; Baron et al., 2017; Rahal,2020)
It is large and sparsely installed
Requires regular maintenance which is
expensive (Rahal, 2020)
Ground-based Station
It is cost efficient, cost US$300 ~ R5400
(www.purpleair.com)
Generally small, and easy to install
Consume little energy (Rahal,2020)
Connected to internet and has an app to
install on the phone
Purple Air Sensor
Image adapted from www.purpleair.com
Wernecke et al.,2021
14. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Conclusion
To collect ambient air data using the PA-II-SD Air quality sensor
• Air data was collected in Stellenbosch using the PA-II-SD Air quality sensor
To determine PM2.5 air pollution sources and investigate on health assessment relative to South
African air quality limits and WHO air quality guidelines
• Ambient PM2.5 in Stellenbosch originates from two sources (Onland & Coast)
• Overall, hourly PM2.5 levels measured daily exceeded the SA NAAQS (40 μg/m3) and the World Health
Organization air quality guidelines (25 μg/m3) on 219 occasions. July registered the most exceedance.
Assess relationship between PM2.5 measure in Stellenbosch and meteorology
PM2.5 showed positive correlation with Humidity and negative correlation with temperature.
• No correlation with wind speed and rainfall
In a nutshell, PAS can be more effective and efficient if installed at different points in the town, to
collect data that can be compiled to give a more detailed measure of PM2.5 in Stellenbosch.
15. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Acknowledgement
• Dr Susanne Fietz
• Andile Malinga
• Liam Quinlan
• South African Weather Services
• Cape Town Municipality
• Stellenbosch University
16. Science · EyeNzululwazi ngezeNdalo · Natuurwetenskappe
Thank you
Enkosi
Dankie
Photo by Stefan Els
Editor's Notes
Every year, air pollution is associated with more than 7 million deaths globally (Forouzanfar et al.,2016)
African continent have shortage of air pollution data
because of the lack of air quality monitoring in these countries.
It makes it hard to assess the health implications of people living in these countries
Low public air pollution awareness
According to 2021 global air quality report, SA ranks position 39 (@22.7ug/m3) on the population weighted 2021 average pm2.5 conc. for 117 countries.
Now, take you through my methodology:
Due to time constraints, I’ll discuss my results as I present them
Measured PM2.5 in Stellenbosch exceeded the WHO air quality guideline (25µg/m3) (World Health Organization, 2021) however, did not exceed the SA NAAQS (40 µg/m3) (Department of Environmental Affairs , 2012)
>>Vulnerability of the children, asthma and TB patients
Now to investigate on the air pollution sources, I came up with potential sources of PM2.5 in stellies
Further defining the potential sources of PM2.5 in Stellenbosch, I investigated the weekdays & weekends PM2.5 variations.
Meaning, PM2.5 measured in Stellenbosch is related to human activities (that mostly take place on weekdays)
Further investigations on the potential sources,
I used a HYSPLIT model by National Oceanic Atmospheric Administration
Red line- represents height of 50m, blue line- 500m and green line- 5000m
The first picture showed that air mass was coming the coast, while other two shows that air mass came from both coastal region and online
I suggested that our PM2.5 originates both from the coast and onland.
A spatial comparison was carried out between Stellenbosch station and Rustenburg Valley station in CT.
And the outcome showed that: Stellenbosch recorded high PM2.5 compared to CT.
Himidity>> +ve correl: With correlation Coefficient of 0.31
Evident throughout the study period because, when Humidity was high, PM2.5 was also high
Temp>> -ve correl: With coefficient of -0.23
When temperatures reached a minimum during overnight, PM2.5 levels showed a slight increase at early hours (2-5am)
WS>> P-Value larger than 0.3 thus not significant and Not statistically correl & rainfall
I suggested that: WS & Rainfall did not influence PM2.5 in Stellenbosch
Now, to give you a brief observation I made on the two data methods
Data showing on the left (PAS), we have on least missing value >>mainly caused by load shedding
However, on the right (GBM), missed capturing a lot of data >>this makes it difficult to use such data
Comparison of the two methods showed that:
In conclusion, all the objectives of the research were addressed.
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