Lockdown during COVID-19 pandemic:A case study from Indian cities shows insignificant effects on persistent property of urban air quality

The influence of reduction in emissions on the inherent temporal characteristics of PMand NOconcentration time series in six urban cities of India is assessed by computing the Hurst exponent using Detrended Fluctuation Analysis(DFA) during the lockdown period(March 24–April 20, 2020) and the corresponding period during the previous two years(i.e., 2018 and 2019). The analysis suggests the anticipated impact of confinement on the PMand NOconcentration in urban cities, causing low concentrations. It is observed that the original PMand NOconcentration time series is persistent but filtering the time series by fitting the autoregressive process of order 1 on the actual time series and subtracting it changes the persistence property significantly. It indicates the presence of linear correlations in the PMand NOconcentrations. Hurst exponent of the PMand NOconcentration during the lockdown period and previous two years shows that the inherent temporal characteristics of the short-term air pollutant concentrations(APCs) time series do not change even after withholding the emissions. The meteorological variations also do not change over the three time periods. The finding helps in developing the prediction models for future policy decisions to improve urban air quality across cities.

Study of ground ozone and precursors along with particulate matter at residential sites in the vicinity of power plant

Emission source characterization and meteorological influence are the key aspects to gain insight into the ground ozone governing mechanisms.Receptor-based data analysis techniques help in comprehending local ozone fluctuations in the lack of accurate information on the emission characteristics.Through sophisticated data analysis,the current study offers insight into the key factors influencing the ozone changes in the vicinity of power plants.Ground ozone(O_(3))and its precursor variables carbon monoxide(CO),nitric oxide(NO),nitrogen dioxide(NO_(2)),Sulphur dioxide(SO_(2)),benzene,toluene,ethyl-benzene and xylene(BTEX)along with the particulate matter of size less than 10 and 2.5 micron(PM_(10) and PM_(2.5))and meteorological variables have been studied at a residential site near the coal-fired power plant in the two cities;Chandrapur and Nagpur during 2016–2019.O_(3) is observed to be not correlated significantly(r<0.16 and<0.1 in Nagpur and Chandrapur,respectively)with any of its precursor variables in two cities.On a finer time scale,however,an association of O_(3) with CO,NO,NO_(2) and BTEX suggested that the O_(3) formation mechanism is driven by volatile organic compounds(VOCs)(mainly BTEX),CO and NO_(x).On the coarser scale,however,seasonality and other factors have distorted the correlation.Random forest model with O_(3) concentration as the response variable and NO_(2),NO,SO_(2),CO,BTEX,PM_(10) and PM_(2.5) as independent variables suggested that PM_(10),NO,CO and solar radiation are highly important variables governing the O_(3) dynamics in Chandrapur.In Nagpur,wind direction,relative humidity,temperature,toluene and NO_(2) are more important.Qualitative analysis to assess the contribution of emission sources suggested the influence of traffic emissions in Nagpur and the dominance of non-traffic related emissions,mainly power plant and mining activities in Chandrapur.The hazard quotient is observed to be>1 in both cities suggesting a health hazard to the residents living in the area.