3.1. Mass concentration of PM2.5 and its metallic composition
The 12-h mean PM2.5 was found to be 262.9 ± 150.7 µg m− 3 during the study period (Table 1). Concentration trends of PM2.5 and meteorological conditions during the day-time and night-time of the study period have been illustrated in Table S3. The 12-h mean PM2.5 (262.9 µg m− 3) was approximately 4.4 times higher than the National Ambient Air Quality Standards (NAAQS) of India (60 µg m− 3) (NAAQS 2009). A day after Diwali (October 28, 2019), particulate concentration reached to highest level of 444.3 and 508.4 µg m− 3 in the day and night, respectively (Fig. 2) whereas, the mass concentration of PM2.5 was 131.3 and 412.1 µg m− 3 in day-time and night-time, respectively on Diwali days (27/10/2019). However, a day prior to Diwali (26/10/2019), the mass concentration of PM2.5 was 108.4 and 153.2 µg m− 3 in day-time and night-time, respectively. A comparison of pollutant concentration at different locations during fireworks is presented in Table 1. PM2.5 mass concentration (262.9 µg m− 3) at the present site during the Diwali period was comparable to that observed at Beijing, China (248.9 µg m− 3, Zhang et al., 2017) during Chinese spring festival. PM2.5 mass concentration at the present site was higher than various other sites around the world including urban area of Marylebone (44.3 ± 17.6 µg m− 3, Godri et al., 2010) and Nottingham (31.2–38.7 µg m− 3, Singh et al., 2015) in UK while the concentrations were lower than that reported at Shanghai, China (775 µg m− 3, Huang et al., 2012), Kolkata (1199.7 µg m− 3, Thakur et al., 2010) and Bhilai (1501.2 µg m− 3, Pervez et al., 2016), India. Similar increase in PM2.5 level has been observed at Delhi (Parkhi et al. 2016) and Dehradoon (Prabhu et al. 2019) in India during Diwali. It was also observed that the PM2.5 mass concentration was higher during night time as compared to day time due to intense firework activity during night-time (Fig. 2). Apart from the burning of firecrackers, the meteorological conditions might have contributed to delayed dispersion of pollutants too (Ganguly et al. 2019). During Diwali period low relative humidity 42% in day-time was observed which increased upto 63% in night-time while, the wind speed ranged from 0.9–1.2 m/s during day-time and 0.4–0.8 m/s in night-time resulting in decrease in boundary layer height, making the atmosphere less conducive to dispersion and dilution of pollutants. The predominant wind direction was West- north west (W-NW) during the study period (Table S3).
Table 1
Comparison of Ambient pollutant concentrations of normal, pre- Diwali and post-Diwali days to Diwali day with similar firework studies
Event | City, Country | Study period | Ambient pollutant concentration (µg m− 3) | DTT Activity |
PM2.5 | PM10 | O3 | CO | NOx | SO2 | DTTv (nmol min− 1 m− 3)/ DTTm (pmol min− 1 µg− 1) |
aGuy Fawkes Night (Godri et al. 2010) | Marylebone, UK | 2007 | 44.3 ± 17.6 | - | - | - | 83.3 ± 3.5 | 23.6 ± 4.0 | 6.5 ± 1.5 (DTTm) |
bDiwali (Thakur et al. 2010) | Kolkata, India | 2008 | 1199.7 | 2237.2 | - | - | 94.5 | 12.3 | - |
cChinese Spring Festival (Huang et al. 2012) | Shanghai, China | 2009 | 775 | > 900 | - | - | 286 | 438 | - |
dCommonwealth Games (Beig et al. 2013) | New Delhi, India | 2010 | > 2000 | > 2500 | - | - | - | - | - |
eDiwali (Saha et al. 2014) | Kolkata, India | 2013 | - | 875 | - | - | 190 (NO2) | 125.21 | |
fGuy Fawkes Night (Singh et al. 2015) | Nottingham, UK | 2000–2012 | 31.2–38.7 | 37.4 | - | - | - | - | - |
gDiwali (Pervez et al. 2016) | Bhilai. India | 2012 | 1501.2 | - | - | - | - | - | - |
hDiwali (Parkhi et al. 2016) | New Delhi and NCR India | 2010 and 2011 | 1620 in 2010, 390 in 2011 | 2070 in 2010, 600 in 2011 | > 50 ppbV | 5–10 ppmV | - | - | - |
iChinese Spring Festival (Zhang et al., 2017) | Beijing, China | 2015 | 248.9 | - | - | - | - | 57.8 | - |
jDiwali (Ambade 2018) | Jamshedpur, India | 2014 | - | 500.5 | - | - | 73.4 | 8.6 | - |
kDiwali (Prabhu et al. 2019) | Dehradoon, India | 2017 and 2018 | 79.92– 324.97 | 57.35–256.12 | - | - | - | - | - |
lGuy Fawkes Night (Rindelaub et al. 2021) | Auckland, New Zealand | 2019 | - | 35.8 | - | - | - | - | - |
mDiwali (Singh et al. 2020) | Delhi, India | 2018 | - | 974.55 | - | - | - | - | - |
nDiwali (Present study) | Agra, India | 2019 | 262.9 ± 150.7 | - | 26.3 ± 13.0 | 1.4 ± 0.4 | 70.3 ± 26.2 | 15.8 ± 2.2 | 0.28 ± 0.46 (DTTv) and 5.05 ± 4.03 (DTTm) |
a−mOther firework studies; 24-h average during study period |
nPresent study; 12-h average during study period. |
Firework activity during late evening and night may cause increased emissions of metal oxides, metal salts and other inorganic species. Figure 3a illustrates the variation of trace metals such as Ba, Be, Cd, Cr, Cu, Mn, Ni, Pb, Se, V, and Zn, whereas, the variation of crustal metals such as Al, Ca, Fe, K, Mg, and Na is represented in Fig. 3b. Among all the seventeen metals, Fe, K, Mg and Na were identified as the major metals with concentrations above 50 ng m− 3. Al, Ba, Ca, Cu and Zn varied from 1 to 50 ng m− 3 while Be, Cd, Cr, Mn, Ni, Pb, Se and V and were mostly between 0.1 and 1 ng m− 3. The concentration of V was lowest (< 0.1 ng m− 3). The concentration of metals was found in the order of Na > Fe > Mg > K > Ca > Zn > Ba > Al > Pb > Cu > Be > Cr > Ni > Se > Mn > Cd > V. Ba, Ca, Cr, Ni, Se, Cu, Be, V, Mg, Zn, and Cd were found to be 5.0, 2.7, 2.4, 2.0, 2.0, 2.0, 1.8, 1.8, 1.6, 1.5, and 1.4 times higher, whereas Mn and K were moderately higher than the levels observed during pre-Diwali.
Ba, as a tracer of fireworks (Lin 2016), has the maximum contribution among these metals which could be due to the extensive use of various salts of Ba, such as barium sulphate (BaSO4), barium oxalate (BaC2O4), barium carbonate (BaCO3), barium nitrate (Ba(NO3)2), barium chlorate (Ba(ClO3)2), in the firecrackers to impart green colour to the flashes (Kulshrestha et al. 2004). Additionally, salts of Al (white), Na (yellow), Cu (blue) and Mg (bright white) contribute to creating a range of colors in the fireworks (Moreno et al. 2007), however, In contrast, Fe plays a vital role in producing sparks, while Ca enhances the intensity of colour created by other elements. Similarly, rest of the metals are also used in fireworks to add color and sparkle. Thus, the high concentration of these metals on Diwali day may be attributed to the presence of various salts of color-producing metals (Hickey et al. 2020; Rindelaub et al. 2021). It has also been found that the levels of metal were low during the pre-Diwali and post-Diwali periods, suggesting their retention period was short and weak contribution of other local sources (Kulshrestha et al. 2004). This study found similar levels of Al, Ba, Mg and other metal as previous studies conducted in China (Kong et al. 2015), Taiwan (Tsai et al. 2012), Italy (Vecchi et al. 2008), Spain (Moreno et al. 2007), and India (Kulshrestha et al. 2004; Barman et al. 2008; Perrino et al. 2011).
A backward air mass trajectory analysis can assist in determining the source and pathway of PM which may be due to the fact that PM concentrations are closely related to wind speed and direction. The 72-h backward air mass trajectories in Agra were simulated at 12:00 h (UTC) during Diwali period by using the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Stein et al. 2015) and are represented in Figure S1. The trajectories were short which showed the firework effect is localized within a limited geographic scale during Diwali days from 26/10/2019 to 28/10/2019, suggesting potential needs for local monitoring and control programs.