Black carbon in different climatic seasons of the Brahmaputra River Valley of Northeast India - Field measurements at two different heights and analysis

The subsequent climate-forcing pollutant to carbon dioxide, black carbon (BC) impacts air quality at local to global scales. Its increasing concentration is worrisome in the hilly regions of the Brahmaputra River Valley of Northeast India due to its proximity to the Himalayas. The unprecedented growth in vehicular population and biomass burning are the prime sources. This study analyzes the BC concentrations measured at ten strategic locations in Guwahati for one year from August 2016 to July 2017, covering the four climatic seasons. Five monitoring stations were at a breathing level of 1.5 m, and another five were at a higher level of 15 m. The research determines the effect of the spatial heterogeneity and the hill-effected local wind-flow pattern on BC's relationship at two different heights. The results show that the temporal variation of BC concentrations at higher levels followed the traffic pattern's temporal variation. The local meteorological fluctuations at breathing height interfere with this relationship, affecting the performance of most air dispersion models near traffic intersections or roadways. When compared, the reduction in BC between the two heights showed the highest in monsoon (14.5 +/- 6.4 mu g m(-3)) and the lowest in winter (5.8 +/- 5.5 mu g m(-3)). With Artificial Neural Network (ANN) and the Bland-Altman Plots, BC's relationship between higher and lower heights was reasonably good for pre-monsoon and poor for monsoon. The average BC concentration at breathing level was 22 +/- 11.3 mu g m(-3), and at the higher level, it was 11.5 +/- 5.2 mu g m(-)(3).