Impact of Secondary Aerosols from Crop Residue Burning in Delhi, India: Application of WRF-Chem Modeling

In October-November months, about 30,000 sq-km area in the upwind of Indo-Gangetic Plain (IGP) is subjected to crop residue burning (CRB). The CRB emissions severely impact the air quality in IGP, especially in Delhi. The problem is compounded because of concurrent urban emissions, atmospheric processes and transformation of gases into secondary inorganic aerosols (SIA) and secondary organic aerosols (SOA).

To apportion the role and impact of CRB, a long-term measurement of PM_2.5 and its chemical composition for BC, SIA, SOA and metals was undertaken. PM_2.5 levels were critically high during CRB (417±114 μg/m³) and post-CRB period (342±134 μg/m³). The WRF-Chem was applied for apportioning the CRB contribution.

The WRF-Chem under-predicted most pollutants and increased the deficit between model and measured concentrations during CRB. The results of WRF-Chem were combined with measurements to develop a new better performing model. The new model performed adequately for R-square and other diagnostics. Overall, the contribution of CRB was estimated about 30 - 32 % in Delhi. The break-up of contributions for BC, SIA and SOA was worked for CRB emission for a better understanding and decision making.