Total Vocs Levels In The Pre-, During, And Post Lockdown Periods
The present study focused on determining the significant changes in air pollutants, especially the total Volatile organic compounds (TVOCs) concentrations, during the COVID-19 pandemic in India, especially it’s western part. The VOCs concentrations significantly declined during the lockdown period in 2020 as compared to the corresponding period in 2019 at all of the monitoring stations in Maharashtra. The main factors behind the significant decline in VOC concentrations during the lockdown were near-total restrictions on transport, industrial activities, and the opening of marketplaces. As a result, the levels of total VOC concentrations were found to be 15.45, 2.48, 19.25 µg/m3 for all monitoring stations for pre-, during, and post lockdown periods. The TVOCs concentrations for all monitoring stations ranged between 0.47 µg/m3 (Bandra) and 51.69 µg/m3 (Thane), 0.44 µg/m3 (Chandrapur) and 4.39 µg/m3 (Nashik), and 2.33 µg/m3 (Bandra) and 77.04 µg/m3 (Thane) respectively for pre-, during, and post-lockdown periods (Fig. 2).
The maximum and minimum levels of TVOCs for all three years were observed in Thane and the Bandra monitoring stations, respectively. The trend of TVOCs for among all the monitoring stations was observed to be in order Thane > Nashik > Chandrapur > Bandra during the lockdown period, whereas Thane > Aurangabad > Chandrapur > Bandra for the pre-lockdown and Thane > Aurangabad > Nashik > Chandrapur > Bandra for the post lockdown periods. The TVOCs concentration declined by -84% compared to the levels observed in the previous year.
After the lifting of lockdown, TVOCs gradually increased along with the re-opening of various industries and transport services. This could also be related to the use of private transportation (including private cars and taxis) as people continued practicing social distance and resuming their jobs (Huang et al., 2020). The highest value of TVOCs was observed at Thane, considered an industrial region, and the lowest at Bandra, which was considered a residential region, respectively. The highest TVOCs at Thane may be attributed to petroleum refinery and chemical industries. On the other hand, the reduction percentages for TVOCs have not observed a similar trend during the lockdown periods. This can be generally explained by the changes in the contribution of both solvent use and vehicles exhaust (Qi et al., 2021). A study conducted at different zones in Delhi, the average values of TVOC and ∑BEXT were reported highest (518.9 µg/m3) in heavy traffic density areas during the rush and non-rush hours (Singh et al., 2016) which was much higher than the present study.
Identification Of Vocs Characteristic Pollutants For Pre-lockdown Period
The BTEX concentration for all monitoring stations was presented in Fig. 3 for pre-, during and post lockdown periods. The average levels of VOC for pre-lockdown periods were found to be 2.32, 15.47, 3.15, and 6.32 µg/m3 for Benzene, Toluene, Eth-Benzene, and MP-Xylene, respectively. For pre-lockdown periods, the average VOCs varied from 0.23 to 8.30 µg/m3 for benzene and 1.35 to 40.09 µg/m3 for Toluene at Chandrapur and Thane monitoring stations, respectively. Benzene, toluene, and MP-Xylene’s average VOCs were 8.30, 40.09, and 13.78 at Thane. The maximum VOCs for Benzene, Toluene, Eth-Benzene, and MP-Xylene were 30.15, 112.20, 108.0, and 9.63 µg/m3 for Thane during the year 2019, whereas the minimum that was observed were 0.23, 1.35, and 1.32 at Chandrapur for the year 2019.
The average trend was found to be in order Thane > Bandra > Aurangabad > Chandrapur for Benzene and Thane > Aurangabad > Chandrapur for Toluene, whereas a similar trend was also observed for MP-Xylene during the year 2019. A high level of VOCs was reported at Thane due to the area-defined buffer zone between hazardous industries and residential quarters. Ravindra et al. (2019) claimed that transport was the most significant contributor of VOCs in ambient air; other sources such as industries and petrol pumps also contributed significantly. Furthermore, several studies reported that the major emission sources that were contributing to VOCs were solvent related emissions, renovations, household products, paints, glues, polishes, waxes, and pesticides (Batterman et al. 2007; Schlink et al. 2010; Dunagan et al. 2011; Jia and Batterman 2010; Chin and Batterman 2012; Chin et al., 2014).
Identification Of Vocs Characteristic Pollutants During Lockdown Periods
The average VOCs for all monitoring stations were calculated to be 1.12, 1.63, 0.62, and 0.19 µg/m3 for Benzene, Toluene, Eth-Benzene, and MP-Xylene, respectively during the lockdown period. The average Benzene concentration varied from 0.06 µg/m3 (Chandrapur) to 2.58 µg/m3 (Bandra), whereas for toluene it varied from 0.19 µg/m3 (Chandrapur) to 3.06 µg/m3 (Nashik) during the lockdown period. The VOCs at all stations were recorded below the prescribed limit by CPCB (5 µg/m3) during the lockdown period. The average values reported during the lockdown were minimum due to complete transport and industrial activities restrictions, which are significant sources of primary VOC emissions.
The average trend of benzene was found to be in order Chandrapur > Nashik > Bandra, whereas a similar trend was also observed for toluene during the lockdown period. The maximum values that were calculated were 9.37 µg/m3 (Bandra), 0.16 µg/m3 (Chandrapur), and 1.69 µg/m3 (Nashik) for benzene, 1.05 µg/m3 (Chandrapur), and 8.69 µg/m3 (Nashik) for toluene during the lockdown period. The levels of VOC were reported higher at Chandrapur as compared to other stations due to the presence and continued operation of the Super Thermal Power Station which contributed a significant portion of VOCs during the lockdown period. Power plants were functional during the lockdown period but at a reduced scale due to the decline in electricity demand in industrial and commercial units (Sathe et al., 2020). The values of VOC for all monitoring stations were observed to be lower during the lockdown period than the corresponding period in 2019. The major factors behind the decline in emissions during lockdown have been found to be complete restrictions on activities such as transportation (including road, rail, and air), construction, and industries, except essential services such as medical facilities and electricity. In contrast, a slight increase in VOC was noticed during the second and third phase of the lockdown (April 15 – May 3, 2020) due to conditional relaxation to certain businesses, including agricultural businesses, cargo transportation, trucks, trains, and planes, to operate which were significant sources for VOCs.
Identification Of Vocs Characteristic Pollutants For Post-lockdown Periods
The average VOCs for all monitoring stations were 3.38 µg/m3, 28.54 µg/m3, 1.68 µg/m3 for benzene, toluene, and MP-Xylene, respectively during the post- lockdown period. The average VOCs for all stations varied from 2.33 (Bandra) to 5.33 (Thane) for benzene, 3.28 (Nashik) to 74.14 (Thane) in the post-lockdown period. The average levels for VOCs were found to be the highest at Thane, followed by Aurangabad, Chandrapur, and Nashik. The benzene concentration for Thane was recorded quite high, even above the standard limits, while in Bandra, Chandrapur, and Nashik, the levels were also found to be over the standard limits. The trend for benzene was observed in the order Thane > Chandrapur > Bandra > Nashik, whereas for toluene, the order was Thane > Aurangabad > Nashik (Sfig 1).
The maximum VOCs varied from 2.85 (Bandra) to 18.04 (Thane) for benzene and 8.85 (Aurangabad) to 219.20 (Thane) for toluene. The maximum values of VOCs have observed at Thane, possibly due to this area experiencing the movement of heavy-duty vehicles (Srivastava et al., 2005). Emissions from the refinery and transportation of raw material and products through heavy vehicles in Thane contributed to TVOCs there. Traffic emissions were one of the significant sources at Thane, which is situated within 2 km from the major highways.
Comparative Analysis For Pre-, During, And Post-lockdown Period
The average levels of VOCs for benzene varied from 0.23 to 8.30, .06 to 2.58, and 2.33 to 5.38 for all stations for pre-, during and post lockdown periods, respectively. The VOCs levels drastically decreased by 52%, 89%, 80%, and 97% for Benzene, Toluene, Eth-benzene, and M-xylene, respectively during the lockdown period compared to the corresponding period in 2019 (Sfig 2). A similar study conducted in metro cities in India indicated a decrease of about 80 ± 13%, 75 ± 20%, 88 ± 7%, and 80 ± 16% for benzene, toluene, ethylbenzene, and xylene, respectively, during the first phase of lockdown when compared to the values prior to this time (Pakkattil et al., 2021).
The maximum changes were observed − 76%, -86%, and − 87% for Benzene, Toluene, and M-Xylene respectively at Chandrapur during the lockdown period. On the other hand, the average VOCs for the post lockdown period were recorded much higher at 3.02, 17.5, and 9.05 times than those during the lockdown period. These higher values recorded for post lockdown periods were attributable to the relaxation in lockdown by the government of Maharashtra to activities such as transport (public and private), industrial and construction work, and commercial shops (Patil et al., 2021). On the other hand, a slight increase in VOC emissions can be expected, especially in COVID-19, like the situation when the use of sodium hypochlorite solution as spraying agent in the community disinfection practices (Chatterjee, 2020), and frequent mass use of sanitizers etc. was followed rigorously within the cities to control the spread of the disease (Sathe et al., 2020).
The average changes in TVOCs for all stations declined by 84% during the lockdown period as compared to the corresponding period in the previous year. The TVOCs were observed (2.48 µg/m3) below the prescribed limit during the lockdown period, whereas for pre (15.45 µg/m3) and post (19.25 µg/m3), they were observed higher than the CPCB prescribed limit.
Source Identification Of Vocs
The ratio of Toluene and Benzene ratio (T/B) has been widely used to evaluate the influence of traffic and non-traffic sources for vehicle exhaust contribution to aromatics (Nelson and Quigley, 1984; (Shi et al. 2015). Emissions from vehicles are the primary source for both Benzene and Toluene, but benzene is also a well-known marker for vehicular exhaust (Miller et al., 2012). A value of less than 2 for T/B indicated that vehicular emissions significantly influenced aromatic emissions (Wang et al., 2016). Several previous studies have reported that ratios lower than 2 indicated a high traffic source contribution (Tiwari et al. 2010; Yurdakul et al. 2013; Jaars et al. 2014; Miller et al. 2012; Miller et al. 2011), whereas higher ratios indicated non-traffic sources and much higher ratio could also show the influence of other industrial activities (Ho et al. 2004).
In the present study, the T/B ratio was calculated to be 21.19, 5.22, and 4.83 for Aurangabad, Chandrapur, and Thane, respectively, which indicated that non-traffic sources were major contributors during 2019. A higher T/B ratio was also attributed to other sources such as industrial emissions and petrol pumps during 2019 (Gaur, Singh, and Shukla, 2016). The highest toluene to benzene ratio was observed at Aurangabad station, which may indicate higher average temperatures and higher incident solar radiations and other sources along with the traffic emissions to have contributed to higher levels of VOCs.
The T/B ratio during the lockdown period varied between 3.19 and 4.33 in Chandrapur and Nashik stations, respectively, indicating traffic and transportation (under the essential activities) as sources of emissions. In the present study, the T/B ratio was found lower in the lockdown period as compared to the pre-lockdown period. This can be attributed to the complete closure of non-traffic sources such as industries and factories during the lockdown. For the post lockdown period, the T/B ratio was found to be in the range between 1.22 (Nashik) and 13.8 (Thane). A higher T/B ratio was recorded for the post lockdown period as compared to the lockdown period. A higher T/B ratio also indicated the influence of resumption of industrial activities and factories. Other studies claimed that if the T/B ratios were nearly equal to 2 or more, it indicates the predominance of traffic emission sources (Kumar et al., 2017; Carlsen et al., 2018). Several literatures have been reported which confirmed the traffic emission sources such in southern Taiwan (4.6) (Hsieh et al., 2006), Izmir, Turkey (1.81) (Hartmann et al., 1997) Cairo, Egypt (2.4) (Khoder, 2007), Bari, Italy (2.0) (Caselli et al., 2010), Delhi, India (2.54) (Hoque et al., 2008), and Sakaka city, Saudi Arabia Kingdom (1.95–6.07) (El-Hashemy et al., 2018).
Health Risk Assessment
This study calculated the health risk assessment for daily exposure, effective yearly exposure, effective lifetime exposure, hazard quotient, and lifetime cancer risk for the pre-, during, and post lockdown periods. Several published reports have classified the toxicological profile of 20 VOCs by the ATSDR, and the National Toxicology Program (NTP) of the U.S., Department of Health and Human Services (DHHS), U.S. Environmental Protection Agency (EPA), Texas Commission on Environmental Quality (TCEQ), National Research Council (NRC) of the National Academies, and the IARC (CDC, 2016; ASTDR, 2012; ASTDR, 2019; Phillips & Haney, 2017; IARC, 1994; EPA, 2020; NRC, 2014) Exposure to the VOCs in the present study indicate acute and chronic health hazards. Many studies claimed that the human health effects of VOCs can be categorized as non-cancer and cancer risks (He et al., 2015; Li et al., 2019). It has been reported that non-cancer risk is mainly associated with chronic damage to the liver and kidney (Rumchev et al., 2007; Singh et al., 2021; Singh et al., 2021c), and cancer risk is primarily reflected in the lung, blood, and brain cancer due to specific exposure (WHO 2000).
Various organizations such as the WHO and the USEPA have established guideline values for BTEX compounds and recommended the limit of LCR (USEPA, 2009). LCR values are considered an indicator of risk; an LCR with the value of 10 − 6 indicates that potential cancer risk in individual cases will be one person per million people (Habeebullah, 2015). Sexton et al. (2007) proposed different levels to determine the risk from air pollutants in the ambient environment. These levels are classified as follows: compounds with a CR value greater than 10− 4 can be defined as a “definite risk”, a value of 10− 5-10− 4 as a “probable risk”, and a value of 10− 5-10− 6 as a “possible risk”.
At all monitoring stations, the present study calculated LCR values for pre-, during, and post lockdown periods for benzene, toluene, and MP-xylene. LCR values of Benzene for pre-, during and post lockdown periods varied from 2.03 x 10− 6 to 3.56 x 10− 5, 2.62 x 10− 7 to 1.11 x 10− 5, and 9.99 x 10− 6 to 2.3 x 10− 5 for males whereas from 2.37 x 10− 6 to 4.15 x 10− 5, 3.06 x 10− 7 to 1.29 x 10− 5, and 1.17 x 10− 5 to 2.69 x 10− 5 for females and from 3.95 x 10− 6 to 6.92 x 10− 5, 5.1 x 10− 7 to 2.15 x 10− 5, and 1.94 x 10− 5 to 4.48 x 10− 5 for children, respectively for all monitoring stations (Table). The highest LCR values at all monitoring stations were calculated at Thane for the post lockdown period, and the lowest was at Chandrapur during the lockdown period.
LCR values of Toluene for pre-, and during lockdown periods were varied from 5.81 x 10− 6 to 1.72 x 10− 4, and 8.36 x 10− 7 to 3.18 x 10− 4 for male whereas from 6.77 x 10− 6 to 2.01 x 10− 4, and 9.75 x 10− 7 to 3.71 x 10− 4 for females and from 1.13 x 10− 5 to 3.34 x 10− 4 and 3.73 x 10− 5 to 6.85 x 10− 5 for children, respectively for all monitoring stations. The LCR values for pre-, during, and post lockdown periods were recorded to be the highest for Thane station, whereas the lowest values were recorded for Chandrapur station among males, females, and children. The LCR values for pre lockdown period varied from 5.64 x 10− 6 to 5.91 x 10− 5, 6.58 x 10− 6 to 6.89 x 10− 5, and 1.1 x 10− 5 to 1.1 x 10− 4 for male, female, and children respectively. The LCR values were recorded to be the highest for Thane station and the lowest for Chandrapur station. A value of LCR for the pre-lockdown period was found to be similar 2.15 × 10− 5 and 2.05 × 10− 5 for male and female residents respectively in China, which indicated a noticeable higher carcinogenic risk for male and female residents. (Qin et al., 2022). The LCR values for all monitoring stations for benzene for pre-, during, and post lockdown periods were higher than the prescribed value (1 x 10− 6), except during the lockdown period, a guideline limit value in some circumstances (Dutta et al., 2009; Ramírez et al. 2012). The LCR values for males, females, and children were similar to Delhi (Kumar et al., 2014). Many studies estimated cancer risk in various cities and reported similar results (Guo et al. 2004; Hoddinott and Lee, 2000; Ohura et al. 2006).