The concentration of BTEX in selected urban areas of Malaysia during the COVID-19 pandemic lockdown

Abstract

Volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylene (BTEX) are air pollutants that harm human health. This study aims to identify BTEX concentrations before the lockdown known as the Movement Control Order was imposed (BMCO), during the implementation of the Movement Control Order (MCO), and then during the Conditional Movement Control Order (CMCO). These orders were introduced during the COVID-19 pandemic in Malaysia. The study utilised data measured by the continuous monitoring of BTEX using online gas chromatography instruments located at three urban area stations. The results showed that the BTEX concentrations reduced by between -38% and -46% during the MCO compared to the BMCO period. The reduction of human mobility during the MCO and CMCO influenced the lower BTEX concentrations recorded at a station within the Kuala Lumpur area. The results of the BTEX diagnostic ratios and principal component analysis showed that the major source of BTEX, especially during the BMCO and CMCO periods, was motor vehicle emissions. Further investigation, using correlation analysis and polar plots, showed that the BTEX concentrations were also influenced by meteorological variables such as wind speed, air temperature and relative humidity.

Keywords: BTEX; COVID-19; Motor vehicle; Movement control order.

Fig. 1

Location of sampling stations in Shah Alam, Cheras and Seremban in Peninsular Malaysia.

Fig. 2

Mobility trend during the BMCO, MCO and CMCO periods in Kuala Lumpur (Google LLC, 2020).

Fig. 3

Time series of the daily mean of BTEX concentrations. Vertical dashed lines represent the three studied stages, before the Movement Control Order, BMCO (1^st January to 17^th March 2020), during the Movement Control Order, MCO (18^th March to 3^rd May 2020), and during the Conditional Movement Control Order, CMCO (4^th May to 31^st May 2020), at (a) Shah Alam, (b) Cheras and (c) Seremban stations.

Fig. 4

Diurnal patterns of BTEX and air temperature at (a) Shah Alam, (b) Cheras and (c) Seremban stations before the Movement Control Order, BMCO (1^st January to 17^th March 2020), during the Movement Control Order, MCO (18^th March to 3^rd May 2020) and during the Conditional Movement Control Order, CMCO (4^th May to 31^st May 2020).

Fig. 5

The polar plot based on total BTEX concentrations with wind speed and wind direction at three stations; 1. Shah Alam during a) BMCO, b) MCO and c) CMCO, 2. Cheras during d) BMCO, e) MCO and f) CMCO, 3. Seremban during g) BMCO, h) MCO and i) CMCO.