Paper No. A21A-0010 2012 AGU Fall Meeting

Stable Carbon and Nitrogen isotopic characterization of bulk atmospheric particles over Indian coastal site (Goa) during monsoon, post monsoon and winter periods of 2011-2012 Kamana Yadav

1*

, Rajesh Agnihotri

2

, Vedula .V.S. Sarma

3

, Supriya G. Karapurkar

1

, Praveen Kumar Poosarla

3

, M. Dileep Kumar

1

1.CSIR- Chemical Oceanography Division, National Institute of Oceanography, Goa, India.

2. CSIR-Radio & Atmospheric Science Division, National Physical Laboratory , New Delhi, India.

3. CSIR-Bio-Geochemistry Lab, National Institute of Oceanography, Visakhapatnam, India.

*Corresponding author Email: [email protected]

1. Introduction and Objectives-

Atmospheric carbonaceous aerosols especially over coastal regions could influence regional biogeochemical cycles of biogenic elements e.g. carbon (C) and nitrogen (N), radiation budgets and hydro-chemistry of wet precipitation. They may have multiple primary sources of natural and anthropogenic origin and may undergo several complex secondary processes after formation before their eventual removal via dry/wet precipitation. Detailed chemical and stable isotopic characterization of such atmospheric particles can greatly help in identifying source and secondary atmospheric processes. Toward this we collected nearly 60 bulk aerosol samples from the roof of National Institute of Oceanography (NIO), Goa ((15.46

 N, 73.8

 E; at a height ~ 55.8 MASL) from mid 2011 to early 2012 and analyzed mass concentrations of total carbon (TC) and total nitrogen (TN) together with their isotopic values ( d 13 C, d 15 N). Overall objectives of the present study are • To determine chemical and isotopic parameters of ambient bulk aerosols present in lower atmosphere over Goa in different seasons e.g. monsoon, post-monsoon and winter periods.

• To assess influence of local meteorological (MET) parameters on measured chemical and isotopic characteristics by analyzing contemporaneous MET data.

2. Study Region Fig. 1

:

Sampling site at Goa (India) and the high volume air sampler (APM 430;

Envirotech

) used for bulk aerosol sampling in the study.

3. Instruments-

 Ambient bulk atmospheric aerosols (TSP) were collected using a high volume air sampler (APM 430 , Envirotech) with typical air flow rate ~1.2 m 3 per minute.

 Mass concentrations of TC & TN and their isotopic composition were measured using Elemental Analyzer (EA) coupled with a Delta V plus stable isotope mass spectrometer (Thermo®) in a continuous flow mode.

4. Methodology-

We have adapted a modified methodology as discussed in detail, in Agnihotri et al. (2011). In brief, aerosol samples were collected on pre-combusted and pre- desiccated Tissue quartz (Pall; size 8×10”) filters. Sub-aliquots of 1 cm diameter were cut from the collected filters. For measurements of TC, TN contents and their isotopic ratios ( d 13 C and d 15 N) one or two aliquots were taken out and placed in pre-clean Tin cups and made round pellets which were then combusted in an Elemental Analyzer connected to a

Delta V

Stable isotope ratio mass-spectrometer (Thermo  ).

13 C/ 12 C and 15 N/ 14 N ratios of sample gases are then measured with respect to automated injections of standard (calibrated) CO 2 Final results are expressed as d 13 C and d 15 N relative to PDB and atmospheric N 2 and N 2 gases.

standards respectively, and defined as: d 13 C and d 15 N = [(R sample /R standard )-1]×1000----------------------- (1) R denotes 13 C/ 12 C and 15 N/ 14 N ratio in sample and standard.

Schematics of isotopic analyses of aerosol samples are shown in Fig.2.

5. Results-

Rounded layered structure Grape-like structure formed of Carbon monomers Crust particles

6. Conclusions-

 The average mass concentrations of TC, TN and TSPM (Fig. 2) during monsoon were found to be 8.15±5, 1.34±0.8, 67.5±31 mg.m

-3 , respectively (n=7). In post monsoon period TC and TN mass concentrations show a substantial increase with 18.4±7.2, 3.16±2.3 mg.m

-3 , respectively (n=6), but TSP concentrations showed a marginal decrease with an average value of 57.7±35 mg.m

-3 . Aerosol samples during the winter of 2011-12 (a total of 30) show highest mass concentrations of TC, TN and TSPM with average values 29.1±9.5, 6.14±2.3, and 109.6±30 mg.m

-3 , respectively.

Triangular flake structure Flattened particle

 A narrow range (average:  22.8±2.7‰) of δ 13 C TC was observed compared to a wider range of δ 15 N (average: 12.7±5.1‰) during entire sampling campaign. Significantly lower d 15 N TN values were found (average: 3.0±0.5‰) during monsoon period as compared to those for post monsoon (average: 12.3±3.8‰) and winter periods (average: 14.2±3.8‰). Lower d 15 N values are similar to those during pre-monsoon period (Agnihotri et al., 2011) and thereby attributable to incorporation of isotopically depleted nitrogenous compounds originating from adjacent Arabian Sea.

Fig 2: Average mass concentrations of TC, TN and TSP (as shown by

circular, square and diamond symbols) along with associated ranges observed (as shown vertical uncertainty bars) in ambient aerosols over Goa during monsoon, post monsoon and winter period of 2011-2012.

6. Future work-

 Inter-relationships among measured chemical and isotopic characteristics of atmospheric bulk aerosols along with local meteorological parameters are being further investigated.

Glass like angular particles

Fig 3:

d

15 N and

d

13 C variations in ambient bulk aerosols over Goa speed with measured TSP concentrations over Goa during monsoon period of 2011-2012.

Rounded particle (bio-aerosol)

References-

 TSP concentrations show covariance with local MET parameters during monsoon. The relationship appears to be weakening during post-monsoon. Winter TSP masses apear not to be influenced by local MET variables (Fig. 4), instead prevailing wind circulation pattern bringing carbonaceous material from north-northeastern parts of India, appears be dominating chemcial and isotopic characteristics of ambient bulk aerosols over Goa (Fig. 3).

Agnihotri, R., Mandal, T. K., Karapurkar, S., Naja, M., Gadi, R., Ahammed, Y. N., Kumar, A., Saud, T., and Saxena, M. (2011) Stable carbon and nitrogen isotopic composition of bulk aerosols over India and Northern Indian Ocean, Atmos. Environ., 45, 2828–2835, 2011

Acknowledgements-

The authors are thankful to Director CSIR-NIO (Goa) for consistent support and facilities. Dr. P. Mehra (NIO) kindly provided contemporaneous meteorological data measured by automated weather station (AWS) installed at NIO-Goa.

 Analyses of inorganic constituents of aerosols such NH 4 + , NO 3 along with other major ions are also being carried out, that will help us to better understand seasonal changes in .

complex tropospheric chemistry in a typical tropical costal environment.

Narukawa, M., K. Kawamura, N. Takeuchi, and T. Nakajima (1999) Distributions of dicarboxylic acids and carbon isotopic compositions in aerosols from 1997 Indonesian forest fires, Geophys. Res. Lett., 26(20), 3101–3104, doi:10.1029/1999GL010810.