Emissions and atmospheric concentrations of α-pinene at an urban site of India: Role of changes in meteorology

The measurements of a monoterpene (α-pinene) were performed by the PTR-TOF-MS instrument at an urban site of India from mid-January to March 2014. The daytime concentration increased from 0.15 ppb in the second-half of January to 0.40 ppb in the second-half of March. Both the nighttime and daytime ratios of α-pinene/benzene in the second-half of March were 2–3 times higher their respective values from mid-January to first-half of February. The ratios of α-pinene/benzene increased from ∼0.27 ppb ppb⁻¹ at lower temperatures to ∼0.51 ppb ppb⁻¹ at higher temperatures indicating the increase of biogenic emissions in March. The concentration of α-pinene exhibited exponential decline with wind speed, but the rate of decrease in February was about twice that for March. The nighttime ratios of α-pinene/isoprene were greater than those measured in the daytime, suggesting temperature-dependent biogenic emissions of α-pinene. From mid-January to March, the increase of ∼53% in the biogenic contributions of α-pinene were associated with the change in meteorological conditions. Our analysis suggests that the combined effect of the northwest wind flow and higher air temperatures in March favored the emissions of BVOCs from local vegetation. The exceptionally high concentrations of α-pinene up to 6 ppb were measured during the Holi bonfire festival. This is the first study reporting the change in α-pinene during winter-summer transition over India. In the urban regions of developing countries, high emissions of BVOCs from vegetation and of NOx from anthropogenic sources can act as a source of ozone.