Spatio-temporal variations of PM2.5 and Respiratory Deposition Dose (RDD) before and during different COVID-19 lockdown phases at Delhi, India

Present study explores pre-lockdown (1^st January-24^th March, 2020) and during lockdown (25^th March-20^th June, 2020) air quality changes in PM_2.5 along with meteorological effects at megacity- Delhi (28.7041°N, 77.1025°E). Alipur (Rural), Okhla (Industrial) and Pusa Road (Traffic dominant area) experienced mean concentrations (S.D.) of PM_2.5 as 87.56(±54.06), 124.45(±73.49) and 62.14(±58.64) µg/m³ before lockdown(BL; 1^st January-24^th March, 2020), while for Lockdown1(L1; 25^th March-14^th April, 2020), PM_2.5 decreased drastically as 39.26(±16.31), 38.01(±15.16) and 31.03(±12.79) µg/m³ and gradually increased during Lockdown2(L2; 15^th April-3^rd May, 2020), Lockdown3(L3; : 4^th May-17^th May, 2020), Lockdown4(L4; 18^th May-31^st May, 2020), respectively. Percentage decrease in PM_2.5 (-69.46%) correlated with outdoor activities of percentage decrease (-70 to -80%) in L1, from BL phase. Exposure assessment study showed, mean Respiratory Deposition Dose-RDD (S.D.) (µg/hr) for fine particles [Particle diameter (Dp) =0.5 µm] for walk and sit mode during BL, as 27.22(±13.53) and 9.90(±4.91) for Alipur, 30.55(±18.04) and 11.11(±6.56) for Okhla, and 28.67(±14.39) and 10.43(±5.23) for Pusa road, and decreased during L1 as 9.64(±4.00) and 3.50(±1.46) for Alipur, 9.33(±3.72) and 3.39(±1.35) for Okhla, and 7.62(±3.14) and 2.77(±1.14) for Pusa road, respectively. Delhiites were exposed to more fine RDD(walk/sit) before lockdown than during lockdown phases. People in sit mode found less exposed to fine RDD, in comparison to walk condition. The people living indoors were affected by outdoor RDD exposure with windows open condition, while exposed to different indoor pollution sources with windows closed condition during lockdown. Authors suggest avoid use of closed conditioned indoors and ACs; frequent opening of windows to lower the RDD and to minimize the COVID-19 virus transmission via particulates.

Keywords: PM_2.5, RDD, COVID-19.