In order to examine the spatial variability of the aerosol characteristics across the Brahmaputra valley, a land campaign was conducted during late winter (February 3–March 2) 2011. Measurements of particulate matter (PM, PM₁₀, PM_2.5) and black carbon (BC) concentrations were made onboard an interior redesigned vehicle. The length of the campaign trail stretched about 700 km, covering the longitude belt of 89.97°–95.55°E and latitude belt of 26.1°–27.6°N, comprising 13 measurement locations. The valley is divided into three sectors longitudinally: western sector (R1: 89.97°–91.75°E), middle sector (R2: 92.5°–94.01°E) and eastern sector (R3: 94.63°–95.55°E). Spatial heterogeneity in aerosol distribution has been observed with higher PM₁₀ and PM_2.5 concentrations at the western and middle sectors compared to the eastern sector. The locations in the western sector are found to be rich in BC compared to the other two sectors and there is a gradual decrease in BC concentrations from west to east of the Brahmaputra valley. Two hotspots within the western and middle sectors with high PM and BC concentrations have been identified. The associated physico-optical parameters of PM reveal abundance of $PM_{2.5}$ aerosols along the entire valley. High population density in the western and middle sectors, together with the contribution of remote aerosols, leads to higher anthropogenic aerosols over those regions. Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) slightly underestimates the measured PM₁₀ and PM_2.5 at the eastern sector while the model overestimates the measurements at a number of locations in the western sector. In general, BC is underestimated by the model. The variation of BC within the campaign trail has not been adequately captured by the model leading to higher variance in the western locations as compared to the middle and eastern locations.

Effort was made to analyse the biological components along with inhalable, thoracic and alveolic particles in aerosol samples collected from nine distinct locations of Northeast India during post-monsoon season (October–November) for the very first time. Microscopic analysis reveals the presence of 70–90% of non-biological particles followed respectively by pollens (9–18%), animal debris (1–12%) and fungal spores (1–6%). The concentration of bacteria in air sample ranges from 45.5 to 645.84 CFU/m$^{3}$. All the bacterial isolates showed sensitivity against broad (Chloramphenicol and Ampicillin) and narrow (Vancomycin and Erythromycin) spectrum antibiotics which indicates lesser threat to human health. Moreover, the concentration of microbial content in the bioaerosol samples are less compared to some of the reported values in other parts of India. The predominant microbial genera in the collected bioaerosol samples were identified as Gram positive Diplobacilli sp. followed by Diplococci sp. Pollens of 10–20 $\mu$m diameter, which are mostly considered as potential allergens, contribute only up to 20% of total pollen content in the bioaerosol sample collected from various locations indicating healthier air.