Radiative effects of pre-monsoon dust and anthropogenic aerosols over India

Recent investigation of aerosols from global aerosol multi-models show that forward model simulations were unable to reproduce the ground-based station-observed aerosol optical depth (AOD) and their spatial distribution over the Indian subcontinent. Estimation of aerosol-induced radiative effects and its impact on climate requires accurate analysis of aerosols optical properties. In the present study high-resolution aerosol transport simulations are carried out with a state-of-the-art Eulerian chemistry-transport model, CHIMERE, forced externally by Weather Research and Forecasting model as a meteorological driver in offline mode. Simulations are carried out over the Indian domain (6° N to 38° N and 68° E to 99.25° E) at a horizontal resolution of 0.25° × 0.25°. The spatial distribution of pre-monsoon mean AOD at 550 nm is compared with satellite observations for the year 2015. The spatial pattern of AOD showing high values in the Indo-Gangetic Plain (IGP, 0.45-0.55) is consistent with the features of observed AOD from satellite retrievals (0.4-0.55) with a slight over-estimation (30%) in the upper-IGP region. The IGP has a higher AOD than most parts of India attributed to high population density and greater emission sources. Large seasonal mean AOD values are also estimated over the Indian state of Telangana (0.5-0.6) which is over-estimated (25%-35%) as compared to satellite retrievals. The simulated AOD is also found to be in good agreement (NMB: 17% for 16 locations) with AOD from ground-based observations (AERONET and individual measurements) at stations over India. Assessment of anthropogenic and dust AOD showed high influence of anthropogenic aerosols over the IGP region while that of dust over north-western region.

Further, the pre-monsoon shortwave radiative perturbation due to total, dust and anthropogenic aerosols over the Indian region is evaluated at surface (SUR), atmosphere (ATM) and top of atmosphere (TOA). The positive value of the radiative effect signifies warming due to aerosols and vice versa for the negative value of the radiative effect. The radiative effect at TOA due to total aerosols is negative over the north-western region and positive for other parts of India. The net radiative effect of total aerosols at the SUR is cooling (-70 to -80 W m^-2) in contrast to warming (+65 to +80 W m^-2) in the atmosphere. The magnitude of radiative perturbations caused by anthropogenic aerosols is higher compared to dust at SUR and ATM. Anthropogenic aerosols have a net warming effect at TOA (+20 to +50 W m⁻²) in contrast to a net cooling effect (-20 to -40 W m^-2) by dust aerosols. The most substantial values of radiative perturbations due to anthropogenic aerosols are observed over the IGP region while the effect of dust aerosols is prominent over the north-western region of India.