This study investigated the chemical composition (carbonaceous species, water-soluble ions and metal elements) of fine particulate matter (PM 2.5 ) emitted by gasoline and diesel vehicles. The emission factors of PM 2.5 , total hydrocarbons (THC), carbon monoxide (CO) and oxides of nitrogen (NO x ) were also determined. The emission measurements were performed for four gasoline and four diesel vehicles on a dynamometer with a constant volume sampling system. Vehicles having larger engines and higher accumulated mileages had higher emission factors of gaseous pollutants. Moreover, the average emission factor of NO x was about 30 times higher for diesel vehicles than for gasoline vehicles. The average PM 2.5 emission factors for gasoline and diesel vehicles were 1.57 mg km -1 and 57.8 mg km -1 , respectively. The ratio of organic carbon to elemental carbon (OC/EC) was found to be a good indicator of gasoline vehicle emissions (OC/EC > 1) and diesel vehicle emissions (OC/EC < 1). Among water-soluble ions, Ca 2+ and SO 4 2had the highest contribution to PM 2.5 emitted by gasoline vehicles, while NO 3 -, SO 4 2and Ca 2+ had the highest contribution to PM 2.5 emitted by diesel vehicles. Na, Ca, Fe and Zn were the top four metal elements in terms of their contributions to PM 2.5 mass for both types of the vehicles, while Cd, Cr, Pb and Sb were some of the toxic metal elements detected in PM 2.5 .

The Indo-Gangetic Plains (IGP) experience high levels of airborne particulate matter (PM), especially during the dry season. Contributing to PM are natural and anthropogenic emissions and the atmospheric transformation of gases to form particles. Regional smog events occur frequently during wintertime and provide an atmospheric medium for aerosol processing. Here, we investigate the chemical composition and sources of PM at a representative site in the northern IGP during the second Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE 2). In Lumbini, Nepal, the 24 h average PM2.5 and PM10 concentrations ranged 48–295 and 60–343 μg m–3, respectively, from December 20, 2017, to January 1, 2018. On average (± standard deviation), PM2.5 was composed of 39 ± 7% organic carbon (OC), 5 ± 2% elemental carbon (EC), and 20 ± 6% secondary inorganic ions (ammonium, nitrate, and sulfate), 2.0% chloride, and 1.3% potassium. Biomass burning was a major PM source, indicated by a median levoglucosan concentration of 3.5 μg m–3. Secondary organic aerosol (SOA) derived from biomass burning was indicated by high concentrations of nitromonoaromatic compounds (e.g., 4-nitrocatechol peaking at 435 ng m–3). During periods of fog, characterized by high relative humidity (RH) and relatively low solar radiation, nitroaromatic concentrations dropped despite levoglucosan remaining high, indicating that their formation was suppressed. Chemical signatures of SOA indicated that volatile organic compound (VOC) precursors were primarily combustion-derived, with small contributions from biogenic VOC. Through molecular markers and chemical mass balance (CMB) modeling, sources of PM2.5 OC were identified as cow dung burning (24 ± 16%), other biomass burning (20 ± 7%), plastic/garbage burning (4.7 ± 3.2%), vehicle emissions (3.1 ± 1.4%), coal combustion (0.3 ± 0.2%), and SOA from monoaromatic VOC (4.1 ± 0.8%), diaromatic VOC (8.9 ± 4.0%), cresol (0.3 ± 0.4%), isoprene (0.4 ± 0.2%), monoterpenes (1.5 ± 0.6%), and sesquiterpenes (3.2 ± 0.7%). Understanding the levels of PM in Lumbini, along with its chemical composition and sources of OC, contributes to a better understanding of regional air quality episodes in the IGP.

Vegetation traffic barriers along roads can be an effective structure to improve roadside air quality and to reduce human exposure to traffic air pollutants. However, the selection of the plant species should be considered as an important design parameter for vegetation traffic barriers because different plant species demonstrate different levels of tolerance to air pollutants. This study compares the air pollution tolerance of different plant species found in the vegetation traffic barriers in the Kathmandu valley. Four biochemical parameters (relative water content, leaf extract pH, total chlorophyll and ascorbic acid) and the dust-capturing potential of plants were analyzed. Out of the nine selected species, Cinnamomum camphora showed the highest tolerance to air pollution based on the air pollution tolerance index. Similarly, Schefflera pueckleri, Psidium guajava and Ficus benjamina were found to be the sensitive species, while Ficus sp., Nerium oleander, Thuja sp., Dypsis lutescens and Albizia julibrissin were found to have a moderate level of tolerance to air pollution. N. oleander had the highest dust-capturing potential. Considering both air pollution tolerance index and dust-capturing potential, C. camphora, N. oleander and A. julibrissin were found to be the most suitable species for the roadside plantation. The findings of this study might have important implications for plant species selection for vegetation traffic barriers.