Browsing by Author "Srinivas Bikkina"

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Atmospheric phosphorus and its geochemical cycling: Fundamentals, progress, and perspectives
(Elsevier B.V., 2023) Xing Diao; David Widory; Kirpa Ram; Lekhendra Tripathee; Srinivas Bikkina; Kimitaka Kawamura; Shaopeng Gao; Xin Wan; Guangming Wu; Qiaomin Pei; Xiaoping Wang; Zhiyuan Cong
Phosphorus (P) is an essential macronutrient for all organisms that can be redistributed between terrestrial and oceanic systems via atmospheric emission, transport, transformation, and deposition. Moreover, since natural P mobilization from the lithosphere to ecosystems is a relatively slow process, the role of atmospheric P seems to play an important role in its cycling. This paper provides a comprehensive review of the analytical methods used for characterizing atmospheric P species and the methods used for identifying P sources (e.g., oxygen stable isotope compositions of phosphate, δ18OP) discussing their respective suitability, advantages, and limitations. While at a regional scale δ18OP of atmospheric P are generally source-specific, at a more global scale these isotope compositions tend to overlap between sources, rendering their tracer potential more difficult. Furthermore, various sources of atmospheric P and their fluxes are compiled, and the potential uncertainties in the estimates of their respective contributions are reviewed, which suggest that more model inter-comparations, parameter optimizations, and field observations are still needed. Moreover, we summarize the long-range transport process controlling P atmospheric dispersion at various scales (focusing on dust and biomass burning). In addition, the transformation mechanism, especially acid dissolution, that modifies the P cycle during its residence time in the atmosphere is depicted. Finally, we propose that land cover may be a potential key control to the atmospheric P deposition rate based on the critical analysis of previously published rates. This review allows us to ultimately propose key recommendations for fostering future research on P geochemical cycling. © 2023
Carbon isotope-constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo-Gangetic Plain
(Wiley-Blackwell, 2017) Srinivas Bikkina; August Andersson; Kirpa Ram; M.M. Sarin; Rebecca J. Sheesley; Elena N. Kirillova; R. Rengarajan; A.K. Sudheer; Örjan Gustafsson
The Indo-Gangetic Plain (IGP) in northern India, Pakistan, and Bangladesh is a major source of carbonaceous aerosols in South Asia. However, poorly constrained seasonality of their sources over the IGP leads to large uncertainty in climate and health effects. Here we present a first data set for year-round radiocarbon (δ14C) and stable carbon (σ13C)-based source apportionment of total carbon (TC) in ambient PM10 (n = 17) collected from an urban site (Kanpur: 26.5°N, 80.3°E) in the IGP during January 2007 to January 2008. The year-round 14C-based fraction biomass (fbio-TC) estimate at Kanpur averages ~77 ± 7% and emphasizes an impact of biomass burning emissions (BBEs). The highest fbio-TC (%) is observed in fall season (October-November, 85 ± 6%) followed by winter (December-February, 80 ± 4%) and spring (March-May, 75 ± 8%), while lowest values are found in summer (June-September, 69 ± 2%). Since biomass/coal combustion and vehicular emissions mostly contribute to carbonaceous aerosols over the IGP, we predict σ13CTC (σ13Cpred) over Kanpur using known σ13C source signatures and the measured δ14C value of each sample. The seasonal variability of σ13Cobs - σ13Cpred versus δ14CTC together with air mass back trajectories and Moderate Resolution Imaging Spectroradiometer fire count data reveal that carbonaceous aerosols in winter/fall are significantly influenced by atmospheric aging (downwind transport of crop residue burning/wood combustion emissions in the northern IGP), while local sources (wheat residue combustion/vehicular emissions) dominate in spring/summer. Given the large temporal and seasonal variability in sources and emission strength of TC over the IGP, 14C-based constraints are, thus, crucial for reducing their uncertainties in carbonaceous aerosol budgets in climate models. © 2017. American Geophysical Union. All Rights Reserved.
Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India
(Blackwell Publishing Ltd, 2016) Srinivas Bikkina; August Andersson; M.M. Sarin; R.J. Sheesley; E. Kirillova; R. Rengarajan; A.K. Sudheer; K. Ram; Örjan Gustafsson
Large-scale emissions of carbonaceous aerosols (CA) from South Asia impact both regional climate and air quality, yet their sources are not well constrained. Here we use source-diagnostic stable and radiocarbon isotopes (δ13C and Δ14C) to characterize CA sources at a semiurban site (Hisar: 29.2°N, 75.2°E) in the NW Indo-Gangetic Plain (IGP) and a remote high-altitude location in the Himalayan foothills (Manora Peak: 29.4°N, 79.5°E, 1950 m above sea level) in northern India during winter. The Δ14C of total aerosol organic carbon (TOC) varied from -178‰ to -63‰ at Hisar and from -198‰ to -1‰ at Manora Peak. The absence of significant differences in the 14C-based fraction biomass of TOC between Hisar (0.81 ± 0.03) and Manora Peak (0.82 ± 0.07) reveals that biomass burning/biogenic emissions (BBEs) are the dominant sources of CA at both sites. Combining this information with δ13C, other chemical tracers (K+/OC and SO42-/EC) and air mass back trajectory analyses indicate similar source regions in the IGP (e.g., Punjab and Haryana). These results highlight that CA from BBEs in the IGP are not only confined to the atmospheric boundary layer but also extend to higher elevations of the troposphere, where the synoptic-scale circulations could substantially influence their abundances both to the Himalayas and over the downwind oceanic regions such as the Indian Ocean. Given the vast emissions of CA from postharvest crop residue combustion practices in the IGP during early Northeast Monsoon, this information is important for both improved process and model understanding of climate and health effects, as well as in guiding policy decision aiming at reducing emissions. © 2016. American Geophysical Union. All Rights Reserved.