Phase-wise analysis of the COVID-19 lockdown impact on aerosol, radiation and trace gases and associated chemistry in a tropical rural environment.

Phase-wise variations in different aerosol (BC, AOD, PM1, PM2.5 and PM10), radiation (direct and diffused) and trace gases (NO, NO2, CO, O3, SO2, CO2 and CH4) and their associated chemistry during the COVID-19 lockdown have been investigated over a tropical rural site Gadanki (13.5° N, 79.2° E), India. Unlike most of the other reported studies on COVID-19 lockdown, this study provides variations over a unique tropical rural environment located at a scientifically strategic location in the Southern Indian peninsula. Striking differences in the time series and diurnal variability have been observed in different phases of the lockdown. The levels of most species that are primarily emitted from anthropogenic activities reduced significantly during the lockdown which also impacted the levels and diurnal variability of secondary species like O3. When compared with the same periods in 2019, short-lived trace gas species such as NO, NO2, SO2 which have direct anthropogenic emission influence have shown the reduction over 50%, whereas species like CO and O3 which have direct as well as indirect impacts of anthropogenic emissions have shown reductions up to 10%. Long-lived species (CO2 and CH4) have shown negligible difference (<1%). BC and AOD have shown reductions over 20%. Particulate Matter (1, 2.5 and 10) reductions have been in the range of 40 to 50% when compared to the pre-lockdown period. The changes in shortwave downward radiation at the surface, diffuse component due to the scattering and diffuse fraction have been +2.2%, -4.1% and -2.4%, respectively, in comparison with 2019. In contrast with the studies over urban environments, air quality category over the rural environment remained same during the lockdown despite reduction in pollutants level. All the variations observed for different species and their associated chemistry provides an excellent demonstration of rural atmospheric chemistry and its intrinsic links with the precursor concentrations and dynamics.

Implementation of Adaptive-Bayesian DStoch technique for obtaining winds from MST radar covering higher altitudes.

It is challenging to estimate winds accurately from higher altitudes using VHF-MST radar. The current study introduces the Adaptive-Bayesian Deterministic Stochastics Technique (ADStoch), which implements an Empirical Bayesian 1D prediction method using stochastics to analyze radar signals. A new and robust estimator for empirical wavelet shrinkage with Gaussian prior of the nonzero mean for wavelet coefficients is presented, which makes the current prior different from other priors. The mean parameters and the prior covariance hyperparameters follow a pseudo maximum likelihood method for computation. Details on the implemented algorithm developed from scratch using C# are also presented. This technique outperforms contemporary techniques discussed in this context that can recover signals buried in noise established based on the analysis of moment and quality. The estimated Wind is cross-validated for accuracy with the observed wind from the GPS radiosonde operated simultaneously. This technique can consistently extract 3D wind that can reach the range of 25.5 km-28.2 km, improving the conventional maximum altitude of 21.2 km in real time for the MST radar. It is concluded that the ADStoch analysis technique can effectively obtain VHF-MST radar signals at significantly higher altitudes, which is helpful in various scientific investigations.

Anthropogenic influence on the changing risk of heat waves over India.

The overarching goal of this paper is to shed light on the human influence on the changing patterns of heat waves in India using the Heat Wave Magnitude Index daily (HWMId). The HWMId obtained from the observational data sets shows a large increase in the heat waves during the past decades. Investigating the effects of natural (e.g., solar variations and volcanic forcings) and anthropogenic (e.g., greenhouse gas emissions, anthropogenic, land use, and land cover) forcings revealed that the anthropogenic factors have cause a two-fold increase in the occurrence probability of severe heat waves in central and mid-southern India during twentieth century. The spatial distribution of maximum HWMId values under natural and all forcings (including anthropogenic) indicates that in most places human activities have increases the frequency, duration and intensity of extreme heat waves. Under the Representative Concentration Pathway (RCP) 4.5, the risk of heat waves is projected to increase tenfold during the twenty-first century. More than ~ 70% of the land areas in India is projected to be influenced by heat waves with magnitudes greater than 9. Furthermore, we find a significant relationship between heat waves and deficits in precipitation. Results show that concurrent heat waves and droughts are projected to increase in most places in India during the twenty-first century.

An empirical method for source apportionment of black carbon aerosol: Results from Aethalometer observations at five different locations in India.

Black carbon (BC) aerosol emitted in incomplete combustion processes is known for causing warming in the climate system also poses serious health issues. Identification of the sources of BC is essential for the development of mitigation strategies to regulate their effects in changing climate. Among different observational and analytical techniques currently available, source apportionment methods based on optical measurements are relatively simple. For example, 'Aethalometer model' was developed based on Aethalometer observations. However, there are a few limitations with this model arising from assumption of wavelength and angstrom exponent pairs. We have developed an empirical method which also relies on Aethalometer observations named as 'Two alpha method' which assumes angstrom exponent from fossil fuel as 1 and estimates bio-mass fraction and angstrom exponent for bio-mass burning. This method has been applied to Aethalometer observations from five different locations (rural, semi-urban and urban) over Indian sub-continent to quantify sources of BC. Fossil fuel is found to be the major source of BC (∼70%) irrespective of the location. Collocated measurements of Carbon Monoxide (CO) over rural site correlated well with derived bio-mass fraction. Results from this study demonstrated the capabilities of empirical method and shall provide spatio-temporal variability in sources of BC if applied to more locations.