The world is currently going through the COVID-19 pandemic which has caused hundreds of thousands of deaths in just a few months. Considering the need for lockdown measures, most countries, including Malaysia, have implemented 'Movement Control Orders' (MCOs) as a prevention step to reduce the deadly spread of this disease. Local and worldwide media have reported the immediate improvement of air quality due to this event. Nevertheless, data on the effects of MCOs on air quality at local scales are still sparse. Here, we investigate changes in air quality during the MCO at an urban area using the air sensor network AiRBOXSense which measures monoxide (CO) and particulate matter (PM 2.5 and PM 10). In this study, air pollutant data during normal days were compared with MCO days using a reference analyser and AiRBOXSense. The results showed that the levels of the measured pollutants dropped by ~20 to 60% during the MCO days at most locations. However, CO in Kota Damansara (KD) dropped to 48.7%, but PM 2.5 and PM 10 increased up to 60% and 9.7% respectively during MCO days. Local burning activities in the residential area of KD are believed to be the main cause of the increased PM levels. This study has proven that air pollutant levels have significantly fallen due to the MCO. This air quality level information showed that the reduction of air pollutants can be achieved if traffic and industry emissions are strictly controlled.

Globally, the COVID-19 pandemic has had both positive and negative impacts on humans and the environment. In general, a positive impact can be seen on the environment, especially in regard to air quality. This positive impact on air quality around the world is a result of movement control orders (MCO) or lockdowns, which were carried out to reduce the cases of COVID-19 around the world. Nevertheless, data on the effects on air quality both during and post lockdown at local scales are still sparse. Here, we investigate changes in air quality during normal days, the MCOs (MCO 1, 2 and 3) and post MCOs, namely the Conditional Movement Control Order (CMCO) and the Recovery Movement Control Order (RMCO) in the Klang Valley region. In this study, we used the air sensor network AiRBOXSense that measures carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter (PM2.5 and PM10) at Petaling Jaya South (PJS), Kelana Jaya (KJ) and Kota Damansara (KD). The results showed that the daily average concentrations of CO and NO2 mostly decreased in the order of normal days > MCO (MCO 1, 2 and 3) > CMCO > RMCO. PM10, PM2.5, SO2 and O3 showed a decrease from the MCO to RMCO. PJS showed that air pollutant concentrations decreased from normal days to the lockdown phases. This clearly shows the effects of ‘work from home’ orders at all places in the PJS city. The greatest percentage reductions in air pollutants were observed during the change from normal days to MCO 1 (24% to 64%), while during MCO 1 to MCO 2, the concentrations were slightly increased during the changes of the lockdown phase, except for SO2 and NO2 over PJS. In KJ, most of the air pollutants decreased from MCO 1 to MCO 3 except for CO. However, the percentage reduction and increments of the gas pollutants were not consistent during the different phases of lockdown, and this effect was due to the sensor location—only 20 m from the main highway (vehicle emissions). The patterns of air pollutant concentrations over the KD site were similar to the PJS site; however, the percentage reduction and increases of PM2.5, O3, SO2 and CO were not consistent. We believe that local burning was the main contribution to these unstable patterns during the lockdown period. The cause of these different changes in concentrations may be due to the relaxation phases during the lockdown at each station, where most of the common activities, such as commuting and industrial activities changed in frequency from the MCO, CMCO and RMCO. Wind direction also affected the concentrations, for example, during the CMCO and RMCO, most of the pollutants were blowing in from the Southeast region, which mostly consists of a city center and industrial areas. There was a weak correlation between air pollutants and the temperature and relative humidity at all stations. Health risk assessment analysis showed that non-carcinogenic risk health quotient (HQ) values for the pollutants at all stations were less than 1, suggesting unlikely non-carcinogenic effects, except for SO2 (HQ > 1) in KJ. The air quality information showed that reductions in air pollutants can be achieved if traffic and industry emissions are strictly controlled.

Rapid development has led to increasing demand for sand, which is the main source of sand brick and other construction purposes. High demand and environmental issues contribute to the shortage of resources and continuous increase in the cost of the material. In order to overcome this matter, there is a need for replacement materials as alternative resources for fine aggregate. In Malaysia, a renewable resource from biomass that can easily be converted to aggregate material is the woody part of kenaf. It is commonly called kenaf core and is available in abundance after the processing of kenaf stem for bast fiber production. The investigations cover thermal conductivity, compressive strength, density, and porosity of Kenaf Core Quarry Dust Bricks (KCQB). Nine (9) types of samples of bricks, plates, and brick wall were prepared by varying the kenaf core contents. M1, M2, M3, and M4 were used as control samples while M5, M6, M7, M8, and M9 were variable samples with different percentages of kenaf core from 5% to 25%. Quarry dust was fixed at 75% for every variable mix and the balance of 25% sand was replaced by kenaf core at 5% intervals, respectively, until the portion of sand was zero. Based on all properties studied, it is found that the addition of kenaf core affected the thermal conductivity, density, porosity, and compressive strength value. Based on all the properties studied, the addition of kenaf core affected the compressive strength, density, porosity, and thermal conductivity. The compressive strength and density decreased as the kenaf core increased. However, the inclusion of kenaf core resulted in higher porosity. Meanwhile, the addition of a kenaf core from 5% to 25% as sand replacement improved the thermal conductivity values from 0.63 W/m• K to 0.42 W/m• K.

In this study, the effect of replacing the river sand with industrial waste and cellulosic waste was investigated. The cellulosic waste use in this study only focuses on kenaf core, while the industrial waste use in this study is quarry dust. The fine aggregate formulation is adjusted with a different percentage of kenaf core. While the quarry dust is fixed at 50% replacement level. The water-cement ratio set for the formulation is 0.75, and the cement-sand ratio fixes at 1:8. The physical properties are measured through compressive strength and density at 28 days. The result shows that 10% is the maximum replacement of sand with kenaf core to produced brick that using 50% of quarry dust. The compressive strength value of the 10% of kenaf core at 28 days is 8.16 N/mm2 while for density is 1830 kg/m3 at 28 days. All the result shows that kenaf core has the potential to be used as a lightweight fine aggregate. But kenaf core needs to combine with other materials that contribute to the strength.

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