Impact of COVID-19 Restriction Measures on Ambient PM 10 Concentrations during Universiti Putra Malaysia Convocation

. The outbreak of COVID-19 resulted in many significant restricted social and economic activities. The pandemic provided unprecedented natural experiment in which the study was specifically conducted to investigate the impact on particulate matters with aerodynamic diameter less than 10 µm (PM 10 ) resulting from the restriction measures taken by the university management to manage COVID-19 during convocation. PM 10 and meteorological parameters (ambient temperature, relative humidity and wind speed) were monitored using TSI Dusttrak aerosol monitor and Kestrel 4500, respectively. Traffic volume was also considered as the significant source of air pollutants due to higher number of vehicles during the event. Two sets of data were collected during peak hours (7.30-9.30 a.m., 12.30-14.30 p.m. and 16.30-18.30 p.m.) on normal working days (before the outbreak in 2018) and during the convocation (after the outbreak in 2022) at two monitoring points along the major road of Persiaran Universiti 1. The results showed that ambient PM 10 concentrations were remarkably reduced by ~65-84%, especially during afternoon peak hours. Parking space allocated far from the main hall area contributed to lower PM 10 concentrations. From the parking space, graduands were required to either walk with guidance or take the provided university buses to go to the main hall. Pearson correlation analysis showed that PM 10 concentrations have significant relationship with the meteorological parameters (p<0.05). However, in terms of traffic emission, it does not necessarily influence solely by the vehicles. From the observation, walking activities by the graduands, students, visitors, etc. around the monitoring areas also contributed to the dust uplifting, hence influencing the level of PM 10 . The study elucidated the influence of COVID-19 restriction measures on PM 10 concentrations which can be a steppingstone towards a better management in reducing the pollutant in the future convocation events.


Introduction
Since the outbreak of Coronavirus disease in 2019 (COVID-19), many countries around the globe have taken mitigation measures by implementing several restrictions.The restrictions were not only limited to medical measures, but also included nonpharmaceutical interventions such as working from home, events restriction, distanced education, travel ban and public traffic suspension [1][2].
In Malaysia, the National Recovery Plan (NRP) was implemented in four (4) phases starting on 15 th June 2021 until 3 rd January 2022.The existing Standard Operating Procedures (SOP) were updated and replaced by a single SOP containing ten (10) requirements that required all related parties to comply when carrying out or participating in any activities on premises including outdoor areas, indoor spaces or in vehicles [3].The SOP was supplemented by nine (9) guidelines, one of which was related to events and ceremonies, including convocation ceremonies in higher education institutions.The institution's management were required to comply to several restriction measures to prevent the spread of pandemic outbreak during the events.Many of these university or college managements limit the number of attendees by only allowing graduands to attend the events.Parents or guardians were only allowed to drop off the graduands at the allocated area and they will then be directed to park at designated parking space.Restriction measures on traffic vehicles during social events were observed to not only gave positive impact on combating the spread of the pandemic but also seen to improve the air quality in the surrounding areas [4].
Previous studies evidenced that restriction measures, especially vehicle restrictive measures applied during the COVID-19 pandemic were found to be a feasible policy for the significant improvement towards better air quality.According to Kanniah et al. [5] the vehicles restriction policy during lockdown period resulted in 9 to 64% reduction related to the concentrations of particulate matters with aerodynamic diameter less than 10 µm (PM10), particulate matters with aerodynamic diameter less than 2.5 µm (PM2.5),nitrogen dioxide (NO2), sulphur dioxide (SO2) and carbon monoxide (CO).Similar trends were also reported in Indian cities where the highest reduction was associated with the particulate matters i.e.PM10 (31%) and PM2.5 (43%), followed by NO2 (18%) and CO (10%) [6].Filonchyk et al. [7] also reported significant reduction on air pollutants concentrations in Poland cities. Krakow city was reported to have the highest reduction of SO2, PM2.5 and PM10 concentrations which were 54%, 48% and 47%, respectively.Meanwhile, NO2 was found to have the most significant reduction in Gdansk city with the reduction of 39%.The vehicle restrictive measures during unprecedented situation create opportunities for studying the impact of mobility restrictions towards the changes in air quality.
Therefore, this paper aimed at investigating the impact of COVID-19 restriction measures undertaken by the university management on air quality, specifically PM10 during convocation events by also considering the influence of meteorological parameters i.e. ambient temperature (AT), relative humidity (RH) and wind speed (WS), and traffic volume (TV).The findings from this study can provide information which would help in creating a better management in reducing the air pollutants in the future convocation and other social events.

Study Area
The study was conducted at University Putra Malaysia (UPM) Serdang's campus (figure 1).This campus is known to be as UPM main campus which consists of north and south sections.North section is where the management building and most faculties and institutes are located, while south section mainly consists of students' residential colleges.The convocation ceremony is normally conducted every year on the main campus, specifically at the university main hall.However, because of the pandemic outbreak, the convocation ceremony was adjourned for two years (in 2020 and 2021) and reassembled in 2022 with several event restriction measures based on the requirements by the government.One of the major restriction measures that was implemented during the commencement is all parents, families and visitors were not allowed to enter the main hall area in the north section of the campus and was guided to park in the allocated parking space located at the south section of the campus.Graduates were required to either walk with guidance on the pathways or take the provided university buses to go to the main hall.The distance of the pathways from the allocated parking space and the main hall is approximately 421 meters.Two monitoring points were selected along the main road named Persiaran Universiti.The monitoring points were selected near pedestrian crosswalks which observed to have high pedestrian movements from students' residential college and bus stops to the faculties' areas.The details of the monitoring points are highlighted in table 1.

Data Collection
The data collection involved five (5) parameters namely particulate matter with aerodynamic diameter of less than 10 μm (PM10) and meteorological parameters i.e. ambient temperature (AT), relative humidity (RH) and wind speed (WS) as well as traffic volume (TV).Meteorological parameters were considered in this study due to the influential factors on PM10 levels [8].Meanwhile, TV was also considered in the study as a significant source of air pollutants due to the higher number of vehicles during the event.The data were collected during peak hours (7.30-9.30a.m., 12.30-14.30p.m. and 16.30-18.30p.m.) on normal working days (before the outbreak in 2018) and during the convocation (after the outbreak in 2022) at both monitoring points with interval of 15-minute.TSI DustTrak II Handheld Aerosol Monitor and Kestrel 4500 Pocket Weather Meter were used to collect data for PM10 and meteorological parameters, respectively.TSI DustTrak II Handheld Aerosol Monitor used light-scattering laser as detection principle to monitor real-time aerosol mass readings with detection range between 0.001 to 150 mg/m 3 .Meanwhile, Kestrel 4500 Pocket Weather Meter involved several sensors depending on the measured meteorological parameters.AT was monitored based on the thermally isolated sensor with the detection range between -29.0°C to +70.0°C.As for RH and WS, the data were monitored via the polymer capacitive sensor and impeller sensor, respectively.The detection range for RH is in between 5% to 95%, while for WS is in between 0.4m/s to 40m/s.

Data Analysis
A descriptive statistical analysis was conducted based on 15-minute data intervals.In this analysis, data were described based on two typical types of statistics which are the measure of central tendency and the measure of dispersion.From the analysis, total number of data (N total), mean, standard deviation (SD), minimum values (Min) and maximum values (Max) were obtained to describe the data.Meanwhile, correlation between all the parameters i.e.PM10, AT, RH, WS and TV were computed by using Pearson's coefficient (r) to measure linear association, strength and direction of the relationship between continuous parameters at monitoring points [9][10].
The Pearson correlation coefficient is typically used for jointly normally distributed data.The correlation results can be interpreted into one of the following hypothetical scenarios such as very strong, strong, medium, weak, very weak, and no correlation, where the correlation coefficient size (r) is in the range of 0.91 until 1.00 or -0.91 until -1.00, 0.71 until 0.90 or -0.71 until -0.90, 0.51 until 0.70 or -0.51 until -0.70, 0.31 until 0.50 or -0.31 until -0.50, 0.01 until 0.30 or -0.01 until -0.50 and 0.00, respectively [11].Percentage of reduction of PM10 concentrations was calculated between normal working days (before outbreak) and convocation days (after outbreak) to identify the significant impact of restriction measures taken by the university management in combating the spread of COVID-19 on the level of this pollutant.The formula to calculate the percentage of reduction of PM10 concentrations is shown in equation ( 1):

Results and Discussion
Results from descriptive statistics of the PM10, meteorological parameters and TV both during normal working days (before pandemic outbreak) and convocation days (after pandemic outbreak) are highlighted as in table 2.
The table shows that PM10 concentrations were consistently higher at MP2 regardless of whether before or after pandemic outbreak compared to at MP1.The highest PM10 concentration was recorded during afternoon peak hours with the mean concentration of 413 ± 111 µg/m 3 during normal working hours.However, TV recorded during these hours was the least if compared to MP1 and during convocation days.This signifies that the main contributor to PM10 did not solely come from the traffic emission and vehicle movement.From the observation, during these hours, there were high number of students who used the pedestrian crossing located near to the monitoring point.This might lead to higher PM10 concentrations due to the pedestrian movement which influences the uplifting of the dust near to the monitoring point.According to Qiu et al. [12], movement of pedestrians may be attributed to resuspension of the existing particles which lead to higher PM10 concentrations at the area.Meteorological condition can be the determinant factor contributing to the intensity and manner of dispersion of the particles [13].For wind speed, in some cases, higher PM10 concentrations were observed at lower WS as highlighted during afternoon peak hours (normal working days) and lower PM10 was observed at higher WS during afternoon and evening peak hours (convocation days).Opposite scenario was also found where higher PM10 concentrations were observed at higher WS during morning peak hours (convocation days).These scenarios were related with the mechanisms where the particles either accumulated due to calm condition or lower WS or blown/carried away to/from another areas.Generally, lower WS or calm condition will facilitate more accumulation of the particles whereas greater WS leads to stronger turbulence, resulting in further dispersion of the particles [14][15].As for AT and RH, both of these meteorological parameters were greatly related to the wet precipitation.RH is one of the important drivers of wet precipitation.RH represents the amount of water vapour in the air at the constant temperature.During wet precipitation, lower AT and higher RH were recorded.Wet precipitation is recognized as one of the primary natural processes related to reduction of the particles [16].The scavenging effect of PM10 due to the wet precipitation was manifested by the cloud-water captured or washed away by the raindrops [17][18].TV was observed to be the highest during convocation days especially during morning and afternoon peak hours.This scenario was expected due to higher traffic density as graduates' parents and families were attending the convocation event.The highest TV was observed during afternoon peak at MP1 with the mean of 378 pcu/15-min.Higher TV during these hours was expected as the event took only half a day and ended in the afternoon which indicated the movement of vehicles going back from the convocation event.
According to Pearson's correlation analysis from table 3, PM10 was observed to have significant relationship with meteorological parameters for both monitoring points during normal working days and convocation days.PM10 has a strong positive correlation with AT at MP1 (p<0.01) and very strong negative correlation at MP2 (p<0.01),regardless of the monitoring durations.Inverse correlations were also found between PM10 and RH (p<0.01) for both monitoring points.RH significantly influences PM10 through both physical and chemical processes i.e. wet or dry deposition, conversion of particles from gas to solid, rate of deliquescence and the hygroscopic growth [19][20].Previous studies indicated that higher RH was conducive to particle deposition.For instance, strong evaporation and transpiration in the presence of water could form a microclimate with lower AT and higher RH compared with the surrounding environment which may reduce the conversion rate from gaseous to particles and favor particle deposition [21][22].This explained the inverse correlation between PM10 and RH.As for the WS, positive correlations with PM10 were found in MP1 (p<0.05) while inverse correlations were found in MP2 (p<0.01).PM10 concentrations varied with the wind level.PM10 concentrations were also influenced by mechanisms where the particles either accumulated due to calm condition or lower WS or blown/carried away to/from another areas.These will lead to a positive or negative relationship between WS and the pollutant [14][15].Nevertheless, this pollutant was reported to have positive medium correlation with TV (r=0.540,p<0.01)only during normal working days at MP1 while there is no significant relationship (p>0.05) during other monitoring durations.This can be emphasized that PM10 concentrations were not entirely influenced by the traffic vehicles.Another factor can be the cause of high PM10 concentrations in the monitoring areas.From the observation, pedestrian movement especially at the crosswalk contributed to resuspension of particles which influence the PM10 levels [12].
Table 4 indicates the percentage of reduction of PM10 concentration during the convocation days after the pandemic outbreak.From the results, it emphasized that there was a major reduction of this pollutant especially during afternoon and evening peak hours where the percentage values were approximately in between 75-84%.However, it is recorded that there was a slight increase in PM10 during convocation days in the morning peak hours which is less than 36%.Overall, the reduction of PM10 was significant with percentage values of 64.60% and 68.11% at both MP1 and MP2, respectively.This significant reduction of PM10 was expected due to the implementation of restriction measures taken by the university management to prevent the spread of pandemic outbreak during the convocation event as required by the government.The limitation of vehicle used and farther allocated parking space from the main hall area were found to reduce the PM10 and improve the air quality significantly.This supports the impact of vehicle restriction policies on reducing air pollution [23].

Conclusion
The findings from this study represent an opportunity to implement future environmental protection measures regardless of the pandemic situation to maintain the best air quality within the study area.The results show that even short-term changes in anthropogenic activity can significantly affect the PM10 concentrations.During the study periods, air quality was found to be improved with ~65-84% PM10 concentrations reduction during the convocation event after the pandemic outbreak mostly due to the vehicle restrictive measures imposed by the university management.Although changes and policies related to managing COVID-19 were developed for temporary measures, with the findings from this study, it can be seen as a steppingstone in paving the ways to implement long-term vehicle restriction policies in the future.
The publication of this paper is not funded under any grant scheme.However, the authors would like to thank Universiti Putra Malaysia for providing the facilities and supports for this research.

Table 2 .
Descriptive statistics of the PM10 concentrations, meteorological parameters and traffic volume at monitoring points during peak hours of normal working days and convocation days.Normal working days (before the pandemic outbreak)During convocation days (after the pandemic outbreak)

Table 1 .
Details of the monitoring points.

Table 3 .
Pearson's correlation matrix of PM10, meteorological parameters and traffic volume

Table 4 .
Percentage reduction of PM10 concentration at monitoring points