Stable carbon and nitrogen isotopic composition of fine mode aerosols (PM_2.5) over the Bay of Bengal: impact of continental sources

Figures & data

Fig. 1 Seven-day isentropic air mass back trajectories (AMBTs) computed using hybrid single particle Lagrangian-integrated trajectory model, HYSPLIT-4 (Draxler et al., 1999) for the sampling days (27 December 2008 to 26 January 2009) along the cruise track in the Bay of Bengal. Blue pins and red dots over the Indo-Gangetic Plain represent the locations of coal-fired power plants and MODIS-derived fire spots, respectively.

Table 1. Statistical description of mass concentrations (in µg m⁻³) of chemical constituents and stable carbon and nitrogen isotopic compositions (δ¹⁵N and δ¹³C) in PM_2.5 collected over the Bay of Bengal during January 2009

Parameter	IGP-outflow (N=15)	SEA-outflow (N=16)	t-Score, df, p-value
^aPM2.5	13.2–76.7 (38.0±20.2)	2.0–35.3 (22.3±9.9)	2.8, 29, <0.05
TN	0.6–8.8 (3.7±2.5)	0.2–3.0 (1.4±0.8)	3.7, 29, <0.05
TC	3.6–15.4 (8.1±4.3)	1.1–6.5 (3.8±1.8)	3.4, 29, <0.05
TC/TN	1.3–9.4 (3.0±2.1)	1.9–5.4 (2.9±0.8)	0.1, 29, >0.05
δ^13CTC (‰)	−25.0 to −22.8 (−23.8±0.6)	−26.9 to −24.2 (−25.3±0.9)	7.3, 29, >0.05
δ^15NTN (‰)	+11.8 to +30.6 (20.4±5.4)	+10.4 to +31.7 (19.4±6.1)	0.5, 29, <0.05
^aOC	1.6–11.6 (5.9±3.7)	0.2–5.3 (2.6±1.9)	3.0, 27, <0.05
^aEC	0.8–5.0 (2.0±1.3)	0.2–1.8 (1.2±0.4)	2.4, 29, <0.05
WSOC	1.5–8.3 (4.4±2.4)	0.5–4.1 (2.3±1.4)	2.9, 29, <0.05
WIOC	0.0–4.5 (1.6±1.4)	0.0–1.8 (0.6±0.5)	2.6, 29, <0.05
^a	0.4–10.1 (4.4±3.0)	0.3–4.1 (2.1±1.2)	2.7, 29, <0.05
^anss-	1.6–28.5 (11.8±7.8)	1.3–12.1 (7.0 ±3.1)	2.3, 29, <0.05
( /nss- )equivalent	0.62–1.12 (0.92±0.15)	0.60–0.93 (0.78±0.11)	3.2, 29, <0.05
nss-K^+/EC	0.19–0.51 (0.29±0.09)	0.23–0.52 (0.39±0.09)	3.0, 29, <0.05
nss- /EC	1.3–14.5 (6.2±3.6)	2.7–10.3 (6.2±2.2)	0.01, 29, >0.05

^aSupporting parameters were obtained from Kumar et al. (2010).

Fig. 2 (a) Comparison of mass concentrations of total carbon (TC) measured by elemental analyser coupled to isotope ratio mass spectrometer (EA-irMS) versus estimated TC concentration based on the atmospheric abundances of elemental and organic carbon (as EC+OC, measured on Sunset Carbon Analyzer), and (b) correlation plot between total nitrogen (TN) measured by EA-irMS and water-soluble inorganic nitrogen (i.e.

and

) in PM_2.5 samples collected over the Bay of Bengal during January 2009 cruise.

Fig. 3 Spatial distributions of (a) stable carbon (δ¹³C_TC) and (b) nitrogen (δ¹⁵N_TN) isotopic composition of fine mode (PM_2.5) aerosols collected from the marine atmospheric boundary layer of the Bay of Bengal during a winter cruise (27 December 2008 to 28 January 2009).

Fig. 4 Correlation plots for (a) TN versus δ¹⁵N_TN, (b) TC versus δ¹³C_TC, (c) nss-K⁺ versus δ¹³C_TC and (d) WSOC versus δ¹³C_TC for fine mode aerosols collected over the Bay of Bengal during a winter cruise (27 December 2008 to 28 January 2009).

Fig. 5 Comparison of δ¹³C of aerosol-TC over the BoB during a winter cruise (January 2009) with literature values of various sources such as combustion/emissions from C₃, C₄ and marine phytoplankton (Turekian et al., 1998; Cao et al., 2013), coal combustion (Mori et al., 1999; Widory, 2006) and vehicular emissions (Widory, 2006; Cao et al., 2013).

Fig. 6 Linear regression analysis between (a) concentration of

and δ¹⁵N, and (b) equivalent mass ratio of

to

and δ¹⁵N in PM_2.5 collected over the Bay of Bengal during a winter cruise (January 2009).

Table 2. Comparison of stable carbon and nitrogen isotopic compositions of aerosols from this study with those documented in the literature over South Asia

Region	Season	Sample type	δ^13C (‰)	δ ^15N (‰)	Reference
Bay of Bengal	Winter (IGP-outflow)	PM2.5	−23.8±0.6	20.4±5.4	This study
Bay of Bengal	Winter (SEA-outflow)	PM2.5	−25.8±0.9	19.4±6.1	This study
Bay of Bengal	Spring–intermonsoon	TSP	−25.6±0.6	10.6±2.7	Agnihotri et al. (2011)
Arabian Sea	Spring–intermonsoon	TSP	−26.5±0.8	1.4±3.2	Agnihotri et al. (2011)
Mumbai	Summer	TSP	−26.5±0.3	20.2±1.2	Aggarwal et al. (2013)
Mumbai	Winter	TSP	−25.9±0.3	22.8±1.4	Aggarwal et al. (2013)
Chennai	Summer and winter	PM10	−25.0±0.6	–	Pavuluri et al. (2011)
Chennai	Winter (day)	PM10	–	25.5±2.4	Pavuluri et al. (2010)
Chennai	Winter (night)	PM10	–	23.0±2.3	Pavuluri et al. (2010)
Chennai	Summer (day)	PM10	–	22.2±4.3	Pavuluri et al. (2010)
Chennai	Summer (night)	PM10	–	24.3±3.6	Pavuluri et al. (2010)
Africa	Summer	PM10	−25.9±0.3	13.7±2.2	Mkoma et al. (2014)

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