Contribution of fossil and biomass-derived secondary organic carbon to winter water-soluble organic aerosols in Delhi, India.

Delhi, among the world's most polluted megacities, is a hotspot of particulate matter emissions, with high contribution from organic aerosol (OA), affecting health and climate in the entire northern India. While the primary organic aerosol (POA) sources can be effectively identified, an incomplete source apportionment of secondary organic aerosol (SOA) causes significant ambiguity in the management of air quality and the assessment of climate change. Present study uses positive matrix factorization analysis on the water-soluble organic aerosol (WSOA) data from the offline-aerosol mass spectrometry (AMS). It revealed POA as the dominant source of WSOA, with biomass-burning OA (31-34 %) and solid fuel combustion OA (∼21 %) being two major contributors. Here we use water-solubility fingerprints to track the SOA precursors, such as oxalates or organic nitrates, instead of identifying them based on their O:C ratio. Non-fossil precursors dominate in more oxidized oxygenated organic carbon (MO-OOC) (∼90 %), a proxy for aged secondary organic carbon (SOC), by coupling offline-AMS with 14C measurements. On the contrary, the oxidation of fossil fuel emissions produces a large quantity of fresh fossil SOC, which accounts for ∼75 % of less oxidized oxygenated organic carbon (LO-OOC). Our study reveals that apart from major POA contributions, large fractions of fossil (10-14 %) and biomass-derived SOA (23-30 %) contribute significantly to the total WSOA load, having impact on climate and air quality of the Delhi megacity. Our study reveals that large-scale unregulated biomass burning was not only found to dominate in POA but was also observed to be a significant contributor to SOA with implications on human health, highlighting the need for effective control strategies.

Production rate variation and changes in sedimentation rate of marine core dated with meteoric 10Be and 14C.

The first measurement of meteoric beryllium-10 (10Be) using Accelerator Mass Spectrometer (AMS) is reported from PRL-AURiS (Physical Research Laboratory-Accelerator Unit for Radioisotope Studies). Strategically, the meteoric 10Be dating method can date events as old as 10 Myr, and its accuracy while dating marine sediment cores has been well tested with magnetic methods. An attempt is made for a comparative study between radiocarbon (14C) and meteoric 10Be dating methods from a 6 m long sediment core collected from the equatorial Indian Ocean. The core was dated using both radiocarbon and meteoric 10Be and results showed remarkable similarity for both methods in terms of the sedimentation rate. A continuous age offset observed within 50 kyr could be due to a continuous influx of sediment with low 10Be content and that may have caused the meteoric 10Be ages to be younger. The sedimentation rate calculated by changing the 10Be depositional flux rate from 1.5 to 2.5 × 10-2 atoms.cm-2.s-1 shows large variation, indicating the choice of appropriate 10Be depositional flux rate for the region. Additionally, being the first meteoric beryllium-10 measurements using AURiS, we have also discussed and reported the laboratory protocols and efficiency based on repeat standard and blank measurements.