Non-methane hydrocarbons (NMHCs) are primary air pollutants having adverse effects on both the atmospheric environment and human health. Additionally, they are vital precursors for the photochemical formation of tropospheric ozone and secondary organic aerosols (SOA). Despite their significance, there are limited online observations of NMHCs in South Asia, particularly in the Himalayan regions. The pristine Himalayan region is influenced by emissions from the Indo-Gangetic Plain (IGP) region, a highly polluted area in South Asia. To address this gap and assess the influence of emissions from the IGP, online in-situ observations of fourteen NMHCs (eight light NMHCs and six aromatic hydrocarbons) were conducted in the Central Himalayas (1958 m AMSL) using a GC-TDS-FID system. This is the first online observations from any mountain site in South Asia. Simultaneously, air samples were collected from an IGP site (554 m AMSL) to understand regional variations. Surface ozone observations were also carried out in the Doon Valley (700 m AMSL), which serves as a bridge between the Himalayas and the IGP. Diurnal variations in NMHCs show daytime higher values at the mountain site, which is typical for a pristine location. Conversely, IGP foothill and valley sites exhibit urban characteristics with lower values in the daytime. Correlation analysis and percentage contributions confirm the major roles of biomass burning at the Himalayan sites and Liquefied Petroleum Gas (LPG) emissions, automobile and domestic combustion at the IGP site. The anthropogenic influences are found to reach the Himalayan site, mainly in spring, which is confirmed by the concentrated weighted trajectory (CWT) analysis. Such influences are limited to the IGP site in winter, primarily due to the shallower boundary layer. The estimated photochemical age varies from about 9 days in winter to about 16 days in summer-monsoon. It is shown that the hydroxyl radical reactivity, ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) are 4–6 times higher at the IGP foothill site compared to the Himalayan site. Propylene, ethylene and n-butane are major contributors to these at both sites. Ethane is found to be most abundant (40%) at the Himalayan site, while propane (27%) at the IGP site. In aromatics, xylene emerges as the most abundant at the Himalayan site, while toluene is at the IGP foothill site. Benzene and ethylbenzene exceed the standard limits (USEPA and WHO), indicating significant health risks to the population of the Himalayan as well as foothill regions. The surface ozone is found to be higher than the 8-hour NAQS limit (50 ppbv) throughout the year, except in July and September at the Doon Valley site. About 9-50% enhancement in spring maximum is attributed to biomass burning. In-situ photochemical ozone production and loss are estimated at ~41 ppbv and ~8 ppbv, respectively. Limited observations from the Doon Valley site indicate an annual loss of 27-37 kilotons of wheat and 14-32 kilotons of rice production due to elevated ozone levels based on exposure metrics analysis (M7 and AOT40) estimates. Model and satellite-based studies demonstrate the NOx-sensitive behavior of ozone production in this Himalayan region, where aromatics exhibit the maximum ozone formation potential among different NMHCs. This work also suggests a rigorous assessment of the percentage contribution of different NMHCs in emission inventories for the Himalayan region. In this pre-thesis-submission talk, a detailed presentation on methodology, analysis and results related to the aforementioned objectives will be made.