Organic and inorganic components of aerosols over the central Himalayas: winter and summer variations in stable carbon and nitrogen isotopic composition

Abstract

The aerosol samples were collected from a high elevation mountain site, Nainital, in India (1958 m asl) during September 2006 to June 2007 and were analyzed for water-soluble inorganic species, total carbon, nitrogen, and their isotopic composition (δ(13)C and δ(15)N, respectively). The chemical and isotopic composition of aerosols revealed significant anthropogenic influence over this remote free-troposphere site. The amount of total carbon and nitrogen and their isotopic composition suggest a considerable contribution of biomass burning to the aerosols during winter. On the other hand, fossil fuel combustion sources are found to be dominant during summer. The carbon aerosol in winter is characterized by greater isotope ratios (av. -24.0‰), mostly originated from biomass burning of C4 plants. On the contrary, the aerosols in summer showed smaller δ(13)C values (-26.0‰), indicating that they are originated from vascular plants (mostly of C3 plants). The secondary ions (i.e., SO4 (2-), NH4 (+), and NO3 (-)) were abundant due to the atmospheric reactions during long-range transport in both seasons. The water-soluble organic and inorganic compositions revealed that they are aged in winter but comparatively fresh in summer. This study validates that the pollutants generated from far distant sources could reach high altitudes over the Himalayan region under favorable meteorological conditions.

Aerosol acidity in a megacity with high ambient temperature and relative humidity of Central China: temporal variation, determining factors and pollution transition effect

“…Ca 2+ was commonly derived from soil or crustal dust and construction activities (Hegde et al, 2016). Ca 2+ in Wuhan showed slightly higher value in winter and spring than those in summer and fall, similar to previous studies (Zhao et al, 2010;He et al, 2012).…”

“…Higher Clconcentrations were measured in winter (2.87±1.25 μg m -3 ), approximately two or three times than those in other seasons. The Na + /Clratio in winter (0.09) was obviously lower than that of seawater (0.557) (Hegde et al, 2016), reflecting the dominance of other sources for Clinstead of sea salt. The weak correlation (R 2 = 0.20, p <0.05) between Cland Na + verified this.…”

Source appointment of nitrogen in PM_2.5 based on bulk δ¹⁵N signatures and a Bayesian isotope mixing model

“…The bulk δ 15 N in atmospheric particulates is mainly determined by the δ 15 N of N precursors (Aggarwal et al, 2013;Hegde et al, 2015). Often, reported δ 15 N values of typical inorganic N sources (Table 1) can be used in studies on sources and fates of atmospheric N (Elliott et al, , 2009Kendall et al, 2007;Kawashima and Kurahashi, 2011;Michalski et al, 2014).…”

“…δ 15 N values) have been used to trace major sources and processes of atmospheric N (Heaton, 1986;Michalski et al, 2004;Kendall et al, 2007;Pavuluri et al, 2010;Savarino et al, 2013). The analysis of bulk δ 15 N in PM 2.5 is a quick method compared to δ 15 N measurements of inorganic and organic N components (Widory, 2007;Hegde et al, 2015;Bikkina et al, 2016), and it does also provide valuable information on δ 15 N of dry N deposition (Yeatman et al, 2001a; than that in rain NH + 4 and gaseous NH 3 (Yeatman et al, 2001a(Yeatman et al, , 2001bJia and Chen 2010;Felix et al, 2013). In a hypothetical model by Heaton et al (1997), the δ 15 N of particulate NH + 4 stabilized at values of 33‰ (an enrichment coefficient) higher than that of NH 3 when NH 3 ↔ NH + 4 equilibrium was achieved at 25 °C.…”

Characterization and remediation of contamination: the influences of mining and other human activities

“…However, Hegde et al (2016) analyzed aerosols from the Himalayas (generally seen as being remote from contaminated sites) and found some worrying results. The carbon and nitrogen contents and isotopic signatures showed anthropogenic influences.…”