Aerosol measurements at the Gual Pahari EUCAARI station: preliminary results from first year in-situ measurements.

The Finnish Meteorogical Institute (FMI), together with The Energy and Resources Institute of India (TERI), contributed to the The European Integrated project on Aerosol Cloud Climate and Air Quality Interactions, EUCAARI, by conducting aerosol measurements in Gual Pahari, India, from December 2007 to January 2010. This paper describes the station setup in detail for the first time and provides 1st year preliminary results from the aerosol in-situ measurements, which include PM and BC masses, aerosol size distribution from 4 nm to 10 μm, and the scattering and absorption coefficients. The seasonal variation of the aerosol characteristics was very distinct in Gual Pahari. The highest concentrations were observed during the winter and the lowest during the rainy season. The average PM₁₀ concentration (at STP conditions) was 177 μg m^-3 and the average PM_2.5 concentration was 120 μg m^-3. A high percentage (4-9%) of the PM10 mass consisted of BC which indicates anthropogenic influence. The percentage of BC was higher during the winter; and according to the diurnal pattern of the BC fraction, the peak occurred during anthropogenic activity times. Another important source of aerosol particles in the area was new particle formation. The nucleated particles grew rapidly reaching the Aitken and accumulation mode size, thus contributing considerably to the aerosol load. The rainy season decreased the average fraction of particle mass in the PM^2.5 size range, i.e. of secondary origin. The other removal, or in this case, dilution mechanism was based on convective mixing and boundary layer evolution. This diluted the aerosol when sun radiation and the temperature was high, i.e. especially during the pre-monsoon day time. The lighter and smaller particles were more effectively diluted. [ABSTRACT FROM AUTHOR]