NOx Emission Inventories

Work on NOx emission inventories over India has been carried out for different fuel combustion and industrial activities by incorporating the most recently available microlevel activity data as well as country-specific emission factors (EFs) at high resolution (Sahu et al. 2012). Recently, top-down NOx emission inventory has also been made for India (Ghude et al. 2013). A strong growth of NOX is found during 2000s as compared to 1990s. All major cities remain as top emitters of NOX.

Modeling Using Global and Regional Models

Chemistry of the atmosphere has been simulated using various types of photochemical models starting from a simple box model to coupled 3D chemistry-transport models. There are several groups in India using such models. A box model is very simple but very useful to understand chemical process, e.g., a study on changes in surface ozone during a solar eclipse (Naja and Lal 1997). Two-dimensional photochemical models have been used to simulate vertical distribution of trace gases and ion chemistry in the atmosphere by groups at PRL and IITM. Coupled chemistry-transport models have become more popular due to advancement in computing power (Beig and Brasseur 2006; Sheel et al. 2010). While these models can incorporate full chemistry and dynamical processes, the resolution is generally limited. Now, Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) is being used to simulate the emission, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology (Kumar et al. 2012). These models are online and are able to run on higher resolution.

ARIES has made an annual simulation of tropospheric ozone and related species using the WRF-Chem model over South Asia, for the first time. The model simulated ozone, CO, and NOx are evaluated using various observations (TES, OMI, and MOPITT). The comparison of model results indicates the capability of the model in reproducing seasonal variations of ozone and CO, but shows some differences in NOx. Largest differences between model simulations and observations are found during spring when intense biomass burning activity occurs in this region and indicate large uncertainties in anthropogenic and biomass burning emission estimates. Additionally, it is shown that inclusion of aerosols and related heterogeneous chemistry can lead to loss of significant amount of ozone (Kumar et al.

2014). The model results indicate that ozone production in this region is mostly NOx limited.

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