Wintertime direct radiative effects due to black carbon (BC) over the Indo-Gangetic Plain as modelled with new BC emission inventories in CHIMERE

Abstract

Abstract. To reduce the uncertainty in climatic impacts induced by black carbon (BC) from global and regional aerosol–climate model simulations, it is a foremost requirement to improve the prediction of modelled BC distribution, specifically over the regions where the atmosphere is loaded with a large amount of BC, e.g. the Indo-Gangetic Plain (IGP) in the Indian subcontinent. Here we examine the wintertime direct radiative perturbation due to BC with an efficiently modelled BC distribution over the IGP in a high-resolution (0.1∘ × 0.1∘) chemical transport model, CHIMERE, implementing new BC emission inventories. The model efficiency in simulating the observed BC distribution was assessed by executing five simulations: Constrained and bottomup (bottomup includes Smog, Cmip, Edgar, and Pku). These simulations respectively implement the recently estimated India-based observationally constrained BC emissions (Constrainedemiss) and the latest bottom-up BC emissions (India-based: Smog-India; global: Coupled Model Intercomparison Project phase 6 – CMIP6, Emission Database for Global Atmospheric Research-V4 – EDGAR-V4, and Peking University BC Inventory – PKU). The mean BC emission flux from the five BC emission inventory databases was found to be considerably high (450–1000 kg km−2 yr−1) over most of the IGP, with this being the highest (> 2500 kg km−2 yr−1) over megacities (Kolkata and Delhi). A low estimated value of the normalised mean bias (NMB) and root mean square error (RMSE) from the Constrained estimated BC concentration (NMB: < 17 %) and aerosol optical depth due to BC (BC-AOD) (NMB: 11 %) indicated that simulations with Constrainedemiss BC emissions in CHIMERE could simulate the distribution of BC pollution over the IGP more efficiently than with bottom-up emissions. The high BC pollution covering the IGP region comprised a wintertime all-day (daytime) mean BC concentration and BC-AOD respectively in the range 14–25 µg m−3 (6–8 µg m−3) and 0.04–0.08 µg m−3 from the Constrained simulation. The simulated BC concentration and BC-AOD were inferred to be primarily sensitive to the change in BC emission strength over most of the IGP (including the megacity of Kolkata), but also to the transport of BC aerosols over megacity Delhi. Five main hotspot locations were identified in and around Delhi (northern IGP), Prayagraj–Allahabad–Varanasi (central IGP), Patna–Palamu (upper, lower, and mideastern IGP), and Kolkata (eastern IGP). The wintertime direct radiative perturbation due to BC aerosols from the Constrained simulation estimated the atmospheric radiative warming (+30 to +50 W m−2) to be about 50 %–70 % larger than the surface cooling. A widespread enhancement in atmospheric radiative warming due to BC by 2–3 times and a reduction in surface cooling by 10 %–20 %, with net warming at the top of the atmosphere (TOA) of 10–15 W m−2, were noticed compared to the atmosphere without BC, for which a net cooling at the TOA was exhibited. These perturbations were the strongest around megacities (Kolkata and Delhi), extended to the eastern coast, and were inferred to be 30 %–50% lower from the bottomup than the Constrained simulation.

Black carbon health impacts in the Indo-Gangetic plain: Exposures, risks, and mitigation

“…Thus, there is value in specifically targeting BC emission reduction over the Indian subcontinent for reducing the adverse health effects due to air pollution effectively. However, BC comprises a small fraction (within 15%) of the total PM 2.5 mass over most of the IGP ( 24 ). The increase in the CVM per unit increase in aerosol mass is, however, 15 times larger for BC than PM 2.5 over the IGP [see concentration-response coefficient per unit of BC mass concentration (β) in the “Population exposures and BC-attributable CVM burden over the IGP” section in Materials and Methods], and hence, a more significant CVM burden due to BC exposures than that due to PM 2.5 is found over the IGP.…”

“…Nevertheless, while using constrained BC emissions in a state-of-the-art chemical transport model, CHIMERE, it is a foremost requirement to obtain the adequate spatial distribution of wintertime BC distribution that favorably represents the present-day ambient values (close to observed). A previous study ( 24 ) examined direct radiative effects due to BC over the IGP, comparing the modeled BC distribution in CHIMERE with five new BC emission inventories. The BC emission inventories implemented in CHIMERE included constrained BC emissions and the latest bottom-up BC emissions (India-based: Smog-India; global: Coupled Model Intercomparison Project phase 6, Emission Database for Global Atmospheric Research-V4, and Peking University BC Inventory).…”

“…The study showed that the modeled BC concentration using the bottom-up emission inventories in CHIMERE is, in general, two to four times lower than that observed over most of the IGP. In comparison, BC simulations with constrained BC emissions in CHIMERE could simulate the distribution of BC pollution over the IGP more efficiently than with bottom-up emissions ( 24 ).…”

Tracing Atmospheric Anthropogenic Black Carbon and Its Potential Radiative Response Over Pan‐Third Pole Region: A Synoptic‐Scale Analysis Using WRF‐Chem

“…Ghosh et al. (2020) stated that BC‐induced radiative perturbation is only responsible for 10%–20% of surface cooling over the IGP region. Our model simulation result shows more negative BC‐induced temperature change is concentrated over EA, coincident with maximum negative surface RF.…”

“…explicitly stated that BC-induced direct RF varies under the meteorological influence and different climate regions.As argued bySong et al (2019), a decrease in LH and SH fluxes compensates for surface radiative cooling, leading to a drop in surface temperature. Both the LH and SH (FigureS4in Supporting Information S1) are more negative over EA than SA, thus it can be inferred that the effect of LH and SH will, in turn, reflect upon different surface RF over SA and EA Ghosh et al (2020). stated that BC-induced radiative perturbation is only responsible for 10%-20% of surface cooling over the IGP region.…”