Abstract
21 of 30 most polluted cities for particulate matter (PM 2.5 ) are in India, yet the distribution, identity and emissions of volatile organic compounds (VOCs) from traffic, which are PM 2.5 and ozone precursors, remain unknown. Here, we measured emission factors (EFs) of 74 VOCs from a range of Indian vehicle-technology and fuel types. When combined with 0.1 ° × 0.1 ° spatially resolved activity data for the year 2015, toluene (137 ± 39 Gg yr 1 ), isopentane (111 ± 38 Ggyr −1 ), and acetaldehyde (41 ± 6 Ggyr −1 ) were top 3-VOC emissions. Petrol-2-wheelers and LPG-3-wheelers emitted the highest VOCs (EFs> 50 gVOC/L) and had highest secondary pollutant formation potential, so their replacement with electric vehicles would improve air quality. EDGARv4.3.2 and REASv.2.1 emission inventories overestimated total road sector emitted VOCs due to obsolete EFs and activity data, in particular over-estimating ethene, propene, ethyl benzene, 2,2- dimethyl butane, CO, NO x while significantly under-estimating acetaldehyde. Nitromethane emissions were missing from previous inventories and with isocyanic acid and benzene contributed significantly to toxic emissions (summed total ~41 ± 4 Ggyr −1 ). Knowledge of key VOCs emitted from the world's third largest road-network provides critical new data for mitigating secondary pollutant formation over India and will enable more accurate modelling of atmospheric composition over South Asia. • Emission factors of 74 VOCs measured for Indian vehicular categories including LPG and CNG vehicles reveal high acetaldehyde. • 0.1 × 0.1° speciated VOC traffic emission inventory over India with updated activity data shows overestimate by inventories. • Petrol 2-wheelers and LPG 3-wheelers had highest pollutant emissions.
Highlights
India has witnessed rapid growth and diversification in its transportation sector in the past decade
While it has been shown that more than 50% of the fine-mode PM1 is made of secondary aerosol originating from gas phase precursors including volatile organic compounds (VOCs) in several Indian cities (Gani et al, 2019; Gawhane et al, 2017; Ojha et al, 2020), no information exists concerning the identity, emissions and distribution of VOCs emitted from the road transport sector over India
The spatial resolution is better than REAS and MIX Asia (0.25 ◦ × 0.25 ◦) and at par with the EDGARv4.3.2 emission inventory
Summary
India has witnessed rapid growth and diversification in its transportation sector in the past decade. Emission inventories used by global and regional chemical transport models to account for traffic emissions over India such as Emission Database for Global Atmospheric Research, EDGARv4.3.2 (Huang et al, 2017) and Regional Emission inventory in Asia, REASv2.1 (Kurokawa et al, 2013) rely on outdated emission factors of two decades or older vehicles and have not been updated for new emission control technology, use of fuel portfolio and fleet composition. Increasing air pollution over India due to both ozone and secondary organic aerosol (Gani et al, 2019; V Kumar et al, 2016), for which NOx and VOCs act as precursors, render the road transport, a key sector for reduction of healthcare costs estimated to be 3% of the Indian GDP due to air pollution alone (World Bank, 2016)
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