Regional Air Quality: Forest Fires Impacts of SO2 Emissions on Air Pollutants in the Himalayan Region of Uttarakhand, India

Sulfur dioxide (SO 2 ) is a toxic with adverse health effects on respiratory tract, eyes, mucous membranes and skin. In the present study, the continuous ground-based SO 2 monitoring has planned over Srinagar Garhwal Valley of Uttarakhand. In the monsoon (M-2018), Post-monsoon (PoM-2018), Winter (W-2019) & Pre-monsoon (PrM-2019) & & M-2019 have high SO 2 concentrations (3.66 ± 2.05 µg/m 3 , 5.54 ± 2.23 µg/m 3 , 6.42 ± 1.79 µg/m 3, 7.56 ± 3.53 µg/m 3 6.45 ± 3.49 µ g/m 3 ) at1900 LT, 2000 LT, 1800 LT, 1900 LT &1900 LT attributed mainly due to biomass burning and long-range transportation of pollutants. A drastic change in the SO 2 concentration has been observed from 4.81 to 17.39 µg/m 3 during May 2019 with a strong correlation of 0.61 with re-counts during extensive forest re. Whereas Jul 2018 (1.07 ± 0.82 µg/m 3 ) showed the lowest SO 2 concentration due to wet scavenging process. Temperature, humidity and wind speed have signicant correlation with SO 2 in different season. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model trajectories and cluster analysis indicate the transportation of air mass from the Gulf region, Sahara Desert, Pakistan, Afghanistan to Srinagar with a signicant contribution of 40.43–72.29% air mass. We have also observed weekend effects (reduction in the pollutant concentration) in Jul 2018, Sep 2018, Feb 2019, Apr 2019 and May 2019.

an increase in forest fore activities in the Himalayas from Mar to May which has led to deterioration in the air quality in Uttarakhand and surrounding areas. In the past, several relevant studies have been carried out in the foothill of Himalaya (Dehradun, Haridwar and Rishikesh) to estimate the SO 2 concentration using a dust sampler but failed to provide better high resolution of SO 2  Srinagar is connected by a national highway (NH-58) whose north end is spared to Mana pass (Indo-China border).
The south end is limited to Ghaziabad via Rishikesh and Haridwar. Every year Srinagar also experiences high tra c from Apr to Oct during a holy ancient Hindu and Sikh pilgrimage of shrines such as Badrinath, Kedarnath, Gangotri, Yamunotri and Hemkund Sahib located in Uttarakhand.

2.2.
Observations and methodological techniques: The SO 2 concentration was measured by using the classical uorescence spectroscopy principle. When SO 2 allowed absorbing ultraviolet (UV) radiation at 200 to 240 nm wavelength, photon emission occurs at 300 to 420 nm in the form of uorescence. The amount of uorescence is directly proportional to the sampled SO 2 concentration. SO 2 analyzer (Echotech serinus 50) sucks sample air by 0.750 SLPM (Standard liter per minute) through the outlet. Further, passed from dust lter and hydrocarbon kicker to remove dust & hydrocarbons from sample air. Now sample air is exposed to UV radiation, which originated from the Zinc discharge tube (800 to 1100 V) in the chamber. The optical bandpass lter produces the same UV radiation at 214 nm and attributes to make photons in all directions. Another optical bandpass lter is used to allow wavelengths about 310-350 nm to photomultiplier for the measurement of the intensity of emitted radiation. The reference detector is also used for the correction of uctuations in lamp intensity (Toth et al. 2020). The instrument is calibrated as per user manual guidelines and described by (Youse an et al. 2020). The collected data was extracted by Airodis (software) in the 5 min resolution and further converted into a one-hour resolution for the observation period from Jul 15, 2018 Humidity (r= 0.028) over Erzurum, Turkey. Furthermore, the simultaneous seasonal variations of wind speed, wind direction and SO 2 concentration have also explained in section 3.6.

Diurnal and monthly variations of SO 2 over SGV:
In the M -2018 season (Fig 3a), the maximum SO 2 concentration was 3.66 ± 2.05 μg/m 3 at the 1900 LT and the minimum was reported of 3.01± 1.31 μg/m 3 in the morning time at 0500 LT. The SO 2 variation is almost constant, i.e. changed by only 0.64 μg/m 3 with an average value of 3.39 ± 1.64 μg/m 3 . The SO 2 starts uctuating from 0000 LT and drops at 0700 LT, after that SO 2 was increasing up to 1200 LT may be due to local anthropogenic and photochemical activities as described in Fig. 3a (Husar and Patterson 1980). Furthermore, a dip was observed at 1400 LT due to change in tra c volume and SO 2 is increasing up to 6.45 ± 3.49 μg/m 3 at 1900 LT due to regional  Table 2 and compared with other locations (Table 3) 3.4 Impact of Forest re on SO 2 : The MODIS and FIRMS data have been used to understand the daily variation of re activities/ re count (Over Uttarakhand) and ground-based SO 2 (Fig. 5a). Furthermore, the signi cant re days have been identi ed and considered as the high re activity period (HFAP) based on the methodology suggested by . If the three-day rolling mean/ running mean exceeds the overall median values, then it has considered as HFAP. have been reported in the south (S) to north (N) direction (Fig. 7d). Now M -2019 follows almost similar trends, but the concentration was high. (Fig. 7e). The wind speed less than 5 m/s indicates the local transport of pollutants over Nainital (Dumka et al. 2015) Therefore, SGV has been affected by the local and transportation of pollutants from different directions in different seasons. The high wind speed also supports the high SO 2 concentration over Srinagar valley possibly due to long-range transport of air mass to SGV (The origin of possible source and air mass have also been explained in section 3.8). In the case of the PoM-2018 and W-2018 seasons, the predominant air mass is coming from the Gulf region, Western Pakistan, Afghanistan, Eastern Rajasthan, Haryana and Punjab to the monitoring site ( Fig. 8b & Fig 8c). But in the case of PrM-2019 season the transportation of air mass is from Iran, Iraq, western Pakistan, Rajasthan, Punjab via Haryana to Srinagar Garhwal in the as well from western Uttar Pradesh (Fig. 8d). A similar trend has been observed for the M -2019 season (Fig. 8e). This result in uences the previous high SO 2 observation during PoM-2018, W-2019 seasons (Fig. 3 & 5). The SO 2 concentration at the monitoring has also been in uenced by long-range transportation as well as regional  (Fig. 9a). In the PoM-2018, the air mass has a dominant contribution of 40.43% from Central Asian and Northern African countries along with 59.56% contribution from Afghanistan side (Fig. 9b). Now, W-2019 & PrM-2019 have remarkable contributions in the range of 61.54% to 72.29% from the Central Asian, Northern African countries along with Afghanistan and Pakistan. But it should be also noticed that Punjab and Rajasthan have 20.60 % to 37.85% contribution during transportation of air mass (Fig. 9c-d). The local contribution of 31.16 % and 26.81% from BOB and Central Asia have observed during M-2019 (Fig. 9e). The air mass from the Arabian Ocean region has only a 14.79% contribution. (Gautam et al. 2021) has reported the signi cant contribution of air mass from the Central Asian, and neighbors countries such as Afghanistan and Pakistan through southwesterly wind over Himalayan cloud Observatory, Badshahithaul (Located 80 km from observation site).  (Fig. 10a). The Punjab, Haryana, Himachal Pradesh (HP) and Jammu & Kashmir (J& K) have signi cant BBAs and therefore, air mass helps to transport the pollutant to SGV during PoM-2018 (Previously explained in Fig. 8b & 9b of section 3.7). Dehradun, Haridwar and Udham Singh Nagar of Uttarakhand (Fig. 1) have also contributed to the local BBAs as depicted in Fig. 10b  (Shaik et al. 2019). The impact of BBAs also re ects in the relatively high concentration SO 2 concentration as compare to M-2018 (Fig. 3b). In W-2019, The BBAs dominantly occur in Uttarakhand due to solid wood & coal burning for warming and cooking purpose. BBAs also contribute to local SO 2 emissions along with the long-range transport of pollutants (Fig. 9c & 10c). Whereas, In the PrM-2019 season (Fig. 10d), the BBAs have a predominant impact on SO 2 may be due to agricultural waste burning and intense forest re in Uttarakhand, J& K, and HP ). According to Fig. 10e  The topography map of the monitoring site around the Department of Physics Hemvati Nandan Bahuguna Garhwal University (A Central University), Srinagar Uttarakhand (India). The observational site is located at the 30º13'36 N (Longitude), 78º48'14 E (latitude) and the elevation of 640 m AMSL. Note:

Air back mass trajectory and
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