Water-soluble organic carbon (WSOC) and methanol-soluble organic carbon (MeS-OC) in ambient PM2.5 over Bhopal, central India, were optically characterized during the COVID-19 lockdowns year (2020) to assess the influence of source reductions on these species and the induced changes in their radiative effects. During the lockdowns (23 March - May 31, 2020), the light absorption coefficients (babs-405) of WSOC and MeS-OC had higher values (75 %-105 %) compared to the corresponding period in 2019. MeS-OC light absorption at 365 nm and 550 nm were about thrice and twice, respectively, compared to WSOC absorption at these wavelengths. Increased fire counts and higher MAC405 (Mass Absorption Cross-section) of MeS-OC and WSOC (8 %-58 %) during the lockdowns compared to the corresponding period in 2019, indicated frequent biomass burning events because vehicular and industrial sources were completely shutdown during this period. Fractional solar radiation absorption (f300-400 nm) by MeS-OC and WSOC normalized by EC absorption was higher (15 % +/- 9 % and 9 % +/- 4 %, respectively) during the lockdowns compared to the corresponding period in 2019. The SFE300-400nm (Simple Forcing Efficiency) values for MeS-OCthis study -> literature and WSOCthis study -> literature were 8 % +/- 5 % and

This study investigates the sensitivity of climate model-predicted surface radiation and surface meteorological parameters to atmospheric aerosols and meteorological data assimilation (meteorological initial and boundary conditions) utilizing the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). For this purpose, three sets of simulations including WRFChemCntrl (WRFChem without meteorological data assimila-tion), WRFChemDA (WRFChem with meteorological data assimilation) and WRFDA (WRF only with meteoro-logical data assimilation) were performed over the South Asian domain. A 12-hourly cyclic 3-dimensional variational (3DVAR) meteorological data assimilation (DA) of in-situ meteorological observations was used to generate WRFChemDA and WRFDA reanalyses, during summer (March-May) 2015. The Carbon Bond Mechanism-Z (CBMZ) gas-phase chemistry with Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) was selected for the chemistry simulations. A reduction in incoming shortwave radiation (-10-60 W/ m2) over the Indian landmass and a slight increase (-10-20 W/m2) over the surrounding oceanic region due to the influence of aerosols in WRF-Chem simulations was observed, suggesting that aerosols effects, were simu-lated by the model successfully. These effects of aerosols were further evident in the model output of other parameters such as outgoing longwave radiation at the surface, 2-m temperature (T2), 2-m relative humidity (RH2), and planetary boundary layer height (PBLH). Our results also show that the inclusion of aerosols in the WRFDA simulations (i.e WRFChemDA) improved the prediction of incoming shortwave radiation but deterio-rated some of the meteorological parameters. However, an improved agreement between model simulated ra-diation, T2, RH2 and PBLH and observations was evident in WRFChemDA output compared to WRFChemCntrl output, reinforcing DA induced improvements in meteorological parameters for a given model set-up.

Energy conservation in brick production is crucial to achieving net-zero carbon emissions from the building sector, especially in countries with major expansions in the built environment. However, widely disparate energy consumption estimates impede benchmarking its importance relative to the steel and cement industries. Here we modelled Indian brick production and its regional energy consumption by combining a nationwide questionnaire survey on feedstock, process variables and practices with remote sensing data on kiln enumeration. We found a large underreporting in current official estimates of energy consumption, with actual energy consumption comparable to that in the steel and cement industries in the country. With a total estimated production of 233 ± 15 billion bricks per year, the brick industry consumes 990 ± 125 PJ yr −1 of energy, 35 ± 6 Mt yr −1 coal and 25 ± 6 Mt yr −1 biomass. The main drivers of energy consumption for brick production are the kiln technology, the production capacity and the fuel mix used. The results suggest that improving operating practices would be a first step in making brick production more energy efficient.

<p>Modern-Era Retrospective analysis for Research and Applications (MERRA-2) generated  PM<sub>2.5</sub>  concentrations are widely used to understand the spatio-temporal variability of PM<sub>2.5</sub> across the globe. Only PM<sub>2.5</sub> data from black carbon, organic carbon, sulphate, sea-salt, and dust are provided by MERRA-2. However, previous studies validated MERRA-2 PM<sub>2.5</sub> concentrations obtained by combining all five species data against in-situ ​total PM<sub>2.5</sub> concentrations. To the best of our knowledge, this is the first study over India to validate MERRA-2 species wise PM2.5 concentrations utilizing in-situ surface measurements made over a site at Bhopal (23.285° N, 22.277° E). Bhopal is one of the eleven COALESCE (Carbonaceous Aerosol Emissions, Source Apportionment and Climate Impacts) network regionally representative sites in India. 24 hour integrated filter-based samples (N = 165) collected during 2019, using the MetOne SASS® speciation sampler were used to measure mass and aerosol species concentrations by a variety of analyses. Our results show that the MERRA-2 well captures the aerosol species data at Bhopal. However, MERRA-2 underestimated the annual mean in-situ concentration of organic carbon, black carbon, and sulphate by 1.9 µg m<sup> -3</sup> (~22 %), 1.3 µg m<sup> -3</sup> (~47 %) and 0.9 µg m<sup> -3</sup> (~11 %), respectively and overestimated the sea salt and dust components by 0.75 µg m<sup> -3 </sup>(~95 %) and 8.5 µg m <sup>-3</sup> (~153 %), respectively.  It is pertinent to note that dust from surface aerosol chemical species measurements was re-constructed using elemental aluminium, silicon, potassium, calcium, titanium, manganese concentrations. Further, the annual mean MERRA-2 PM<sub>2.5</sub> mass (reconstructed from its constituent species) underestimated the average in-situ PM<sub>2.5</sub> mass by 13.55 µg m <sup>-3</sup> (~26.16 %). This underestimation is likely due to aerosol nitrate not being included in the MERRA2 PM<sub>2.5</sub> mass and uncertainties in aerosol species concentrations resulting from limitations in the chemical transport model set-up and emissions inventories. This study discusses the possible causes of disagreements between in-situ measurements and MERRA2 products, in addition to estimating the effect of including nitrate in the MERRA2 PM<sub>2.5 </sub>mass reconstruction.</p>