Developing a vehicle emission inventory with high temporal-spatial resolution in Tianjin, China

Highlights: • A high-resolution vehicle emission inventory was developed using the top-down method. • Vehicle age was negatively correlated with annual average vehicle kilometers travelled. • The vehicle population control policy helped reduce air pollutant emissions. • The spatial distributions of vehicle emissions varied slightly for different pollutants. The vehicle emission inventory is used to describe air pollutants from vehicles quantitatively. Many emission inventories have been developed using the top-down method in China; however, most have a low temporal-spatial resolution. This study utilized the top-down method to develop a vehicle emission inventory with high temporal-spatial resolution in Tianjin, China, a typical megacity experiencing severe vehicle pollution. The relationship between vehicle age and annual average vehicle kilometers travelled (VKT) was investigated by introducing the age-VKT curve, which indicated that the VKT decreased when vehicles get older. The emission estimation showed that light-duty passenger vehicles were the major contributors of carbon monoxide and volatile organic compounds, while heavy-duty passenger vehicles and heavy-duty trucks contributed significantly to nitrogen oxides and fine inhalable particles. China III standard vehicles were the main contributors to all pollutants. High-resolution gridded emissions were obtained using a practical allocation method, which showed that the spatial distributions differed slightly for each pollutant and the emissions changed significantly in a 24-h period. This study presented a comprehensive approach to developing a high-resolution emission inventory that can be utilized to assist in pollution control policy formulation.