Study on ambient air quality of megacity Delhi, India ...

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State Government of Delhi had adopted odd-even scheme on vehicles plying in megacity Delhi to understand and improve the air quality of Delhi.
Study on ambient air quality of megacity Delhi, India during Odd-Even strategy S.K. Sharma1,*• Prerita Agarwal1,2 • T.K. Mandal1 • S.G. Karapurkar3 • D.M. Shenoy3 • S.K. Peshin4 • Anshu Gupta2 • Mohit Saxena1 • Srishti Jain1 • A. Sharma1 • Saraswati1 1

CSIR-National Physical Laboratory, Dr. K S Krishnan Road, New Delhi-110 012, India.

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University School of Environment Management, GGS Indraprastha University, New Delhi-110 078, India.

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CSIR-National Institute of Oceanography, Dona Paula, Panji, Goa 403 004, India

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India Meteorology Department, Ladhi Road, New Delhi-110 003, India.

*Corresponding Author: Sudhir Kumar Sharma Environmental Sciences and Biomedical Metrology Division CSIR-National Physical Laboratory Dr. K S Krishnan Road New Delhi-110 012, India E-mail: [email protected]; [email protected] Phone: +91-11-45609448 Fax: +91-11-45609310

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Abstract State Government of Delhi had adopted odd-even scheme on vehicles plying in megacity Delhi to understand and improve the air quality of Delhi. To understand the effect of odd-even scheme on the concentration of pollutants , we have analysed the concentrations of chemical constituents [organic carbon (OC), elemental carbon (EC), water soluble inorganic components (WSIC), trace elements and stable carbon and nitrogen isotopic composition (δ 13CTC) & N (δ15NTN)] of PM2.5 and PM10 along with mixing ratios of trace gases (NOx, CO, SO2 and NH3) data collected at an urban site of megacity Delhi during first phase (Phase-I: winter 2016) and second phase (Phase-II: summer 2016). During the Phase-I of the scheme, mass concentrations of PM2.5 and PM10 were changed by –13% and –5%, respectively, whereas, concentrations of PM2.5 and PM10 were changed by +18% and +16%, respectively during the Phase-II as compared to before the implementation of the scheme. The analysis of chemical constituents of PM 2.5 and PM10 reveals that the odd-even strategy marginally changed the concentrations (markers) of vehicular emission. In both the phases, mixing ratios of trace gases (NOx, CO, SO2 and NH3) were reduced non-significantly during the odd-even scheme as compared to before the implementation of the scheme.

Keywords: Particulate matter, trace gases, odd-even scheme, vehicles.

1. Introduction The ambient air quality of Delhi and its surroundings is a matter of concern as concentrations of the pollutants are exceeding from National Ambient Air Quality Standards (NAAQS) for several years despite repeated efforts. Several researchers [1-4] have made efforts to quantify the sources of atmospheric pollutants, which are localized, heterogonous and dependent on seasons. In addition, the combined effects from industries, power plants, domestic combustion of coal and biomass and transport (direct vehicle exhaust and indirect road dust) are also contributing [3, 5-6]. A comprehensive study on air pollution and green house gases (GHGs) over Delhi carried out by Sharma and Dikshit [7] reported that the vehicular exhaust contributes 36% of NOx whereas 83% of CO to the ambient air of Delhi. Any exposure to ambient air with CO levels >100 ppm is dangerous to human health (slight headache in 2-3 h and perceptible clinical needs with a 20 h exposure). The study further suggested that the concentration of PM 2.5 contributed by vehicles was up to 25% and 9% during winter and summer seasons, respectively [7]. The other major sources of PM2.5 and PM10 are secondary aerosol, soil dust, biomass burning and fossil fuel combustion (thermal power plants) in Delhi [7,8].

To meet the challenge of urban growth in Delhi, several steps (introduction of CNG in public transport, relocation of industries and introduction of Metro transportation etc.,) have been initiated. The total vehicle population in Delhi would be more than that of three metros, Mumbai, Kolkata and Chennai, put together. Due to the growing awareness about air pollution and its health implications leading to public outcry, both the developed and developing world are making efforts to implement various policies and rules to curb air pollution [3-4]. In a bid to curb the alarming levels of air quality of megacity Delhi, the state government announced an ambitious plan to

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restrict the movement of private vehicles from 1–15 January, 2016 (Phase-I). The plan, known globally as “road space rationing”, would see vehicles with odd-numbered registrations being allowed to ply on odd dates and evennumbered registrations being allowed to ply on even dates of the month between 8 a.m. and 8 p.m., except on Sunday (“Odd-Even strategy”). To reduce the pollutants mainly emitted from transport sector, Delhi Government implemented the similar Odd-Even formula for plying of private vehicles in Delhi from 1-15 January, 2016 (PhaseI) and 15–30 April, 2016 (Phase-II).

In this paper, we present the variation in concentration of pollutants [trace gases (e.g., NH3, NO, NO2, SO2)] and chemical characterization [organic carbon (OC), elemental carbon (EC), water soluble inorganic components (WSIC) and trace metals] of PM2.5 and PM10 of Delhi before-during-after the Odd-Even scheme of 2016. We have also analyzed the stable isotopes of C and N (δ13CTC and δ15NTN) of particulate matter to identify the possible sources of PM2.5 and PM10 before-during-after the odd-even scheme. To assess the actual picture of ambient air quality of any location the calibration of the measuring instruments are essential and they should be traceable to SI units [9]. In the present study we have discussed about the calibration and associated accuracy of the instruments in the “Experimental set up” section.

2. Materials and Methods

2.1

Description of Site The measurement of trace gases (NH3, NOx, CO and SO2) and particulate matter (PM2.5 and PM10) samples

were collected at CSIR-National Physical Laboratory (28°38′N, 77°10′E; 218 m mean sea level), New Delhi beforeduring-after the two consecutive Odd-Even implementation of vehicles (Phase-I and Phase-II). The sampling site represents a typical urban atmosphere, surrounded by huge roadside traffic and agricultural fields in the southwest direction (Fig. 1). This area is under the influence of air mass flow from the northeast to northwest in winter and from southeast to southwest in the summer. In Delhi, the increase in vehicles not only affects the total consumption of fuel but also increases the traffic congestion, vehicles idling time and delay events which ultimately results in more emission of NOx, hydrocarbons, and CO [1]. The temperature of Delhi varies from minimum in winter (November to February) to maximum in summer (March to June). The average rainfall in Delhi during monsoon (July to September) is generally of the order of ~800 mm. The subtropical atmosphere of Delhi and large scale emission of trace gases significantly alter the ambient air quality of Delhi. 2.2 Experimental Set up The mixing ratios of ambient NH3, NO and NO2 were measured precisely and continuously using NH3Analyzer (Model: AC32M&CNH3, M/s. Environment SA, France) which operates on the chemiluminescence method. NH3-Analyser (NH3, NO and NO2 ranges of analyzer) was calibrated before and after the completion of each (Phase-I and Phase-II) odd-even programme using Zero Air Generator (Model: PAG-003, M/s. ECO Physics AG, Switzerland), NIST certified NO (500 ppb ± 5%) and NH 3 span gases (through multi gas calibrator and

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permeation tube). The mixing ratio of ambient SO2 was measured using calibrated SO2-Analyser (Model: APSA 360A, M/s. Horiba Ltd, Japan). The instrument follows the principle of the ultraviolet fluorescence method (with the irradiation of the sample with UV rays (220 nm), it emits the light of different wavelengths (240 nm to 420 nm with a peak at 320 nm) -these wavelength ranges are referred as fluorescence. To distinguish it from the UV light source, the fluorescence light is detected from the right angle direction as it irradiates in all directions). The instrument was calibrated every day using an in-built calibrator for zero and span as well as NIST traceable certified SO2 gas (500 ppb ± 5%). Carbon monoxide was measured using non-dispersive infrared gas filter correlation analyzer (Model: 48CTL; M/s Thermo Environmental Instruments, Massachusetts, USA). CO-analyzer was calibrated periodically using NIST traceable certified CO gas (8.1 ppm ± 5%).

PM10 and PM2.5 samples were collected periodically (twice in a week before and after the scheme and daily during the implementation of the scheme) on quartz fibre filters (prebaked at 550oC) using Particle Sampler (Ecotech, AAS 217 NL and APM 550, Envirotech, India). For PM10 sampling, ambient air is passed through a QM-A filters (filter size: 20×25 cm2) at a flow rate of 1.12 m3 min-1 for 24 h during the sampling period using respirable dust sampler (RDS) (Ecotech, AAS 217 NL). PM2.5 samples were collected on QM-A filters (Filter size: 47 mm) using fine particle sampler (APM 550, Make: M/s. Envirotech, India) with a flow rate of 1 m3 h-1 (accuracy ± 2%) for 24 h. The flow meter of the samplers was calibrated (with the accuracy of ± 2% of Full Scale) with air flow calibrator traceable to national standard. The concentrations of PM10 and PM2.5 (in μg m-3) were calculated on the basis of the difference between initial and final weights of the quartz filters measured by a calibrated micro balance (M/s. Sartorius, resolution ± 10 μg) and dividing it by the total volume of air passed during the study.

In addition, the meteorological parameters (temperature, RH, wind speed, wind direction and pressure, etc) were measured by using sensors of a meteorological tower (4 stages tower of 30 m height), which is 100 m away from the observational site within the same campus. Meteorological tower measures the above mentioned parameters at four different heights (above the ground level). The various sensors are placed in the tower at different levels of 1.5, 10, 20 and 30 m height above the ground level. We use the meteorological data available at 10 m height to correlate the trace gases and particulate matter during the study period. Sampling inlets of all analyzers as well as particle samplers were stationed at ~10 m height above the ground level.

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Chemical Analysis Analysis of OC and EC on ambient PM10 and PM2.5 samples was performed using an OC/EC carbon analyzer

(Model DRI 2001A, Atmoslytic Inc., Calabasas, CA, USA) following the method in Chow et al. [10] with negative pyrolysis areas zeroed. Approximately 0.536 cm2 area of QM-A filter paper was cut using the proper punch and the values were reported as µg cm−2 as given by the instrumental analysis software [11]. The concentrations of water soluble inorganic ionic (Cl−, NO3−, SO42− Na+, NH4+, K+, Ca2+ and Mg2+ etc.,) components (WSIC) of PM10 were determined by ion chromatography (Dionex ICS-3000, Sunnyvale, CA, USA). Calibration standards have been prepared by National Institute of Standards and Technology (NIST, USA) traceable certified standards for

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calibration of IC [The IC was standardized using NIST-USA traceable Standard Reference Material, SRM 3184 (Bromide), 3182 (Chloride), 3183 (Fluoride), 3185 (Nitrate), 3186 (Phosphate), 3181 (Sulphate), SRM 3129 (Lithium), 3152 (sodium), 3141 (Potassium), 3131 (Magnesium), 3109 (Calcium)]. Details of WSIC analysis of PM10 are discussed in our earlier paper Sharma et al. [12-13]. Each filter was analyzed in triplicate with blank filters run to obtain the representative estimates of the concentrations of OC, EC and WSIC in the PM mass.

The

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C/12C and

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N/14N ratios together with TC and TN content were measured using an isotope-ratio mass

spectrometer (IRMS; Delta V plus, Thermo®, Bremen, Germany) coupled with an elemental analyzer (EURO3000, EuroVector, Milan IT). Briefly, two aliquots, each of 11mm were sub-sectioned from each quartz filter and packed in clean tin cups to form compact pellets. These pellets were then analysed in the EA-IRMS in a continuous-flow mode. The final results are expressed as δ13C and δ15N relative to V-PDB (Vienna-Peedee Belemnite) and atmospheric N2 standards respectively and defined as: δ13C and δ15N = ((Rsample –Rstandard)/Rstandard)×1000 13

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(1)

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where, R= C/ C and N/ N

Carbon and nitrogen reference gases were calibrated using international standards with a wide range of isotopic values. Analytical precision was estimated by repeated measurements (after every 5 samples) of a laboratory standard ACA (ε-Amino-n-Caproic Acid; δ13C = −25.3‰ and δ15N = +4.6‰) and an in-house sedimentary standard COD (δ13C = −21.08‰ and δ15N = +7.38‰). Analytical precision was better than ± 0.3‰ for δ13C and δ15N. TC and TN contents in the samples were calculated from a calibration curve made of four ACA standards ranging from 1–4 μmol for N and 6–24 μmol for C [11]. The quantitative elemental analysis (Mg, Al, S, Si, Cl, K, Ca, Ti, Cr, Mn, Fe, Zn, Cr, Br, As and Pb) of PM10 samples was carried out using non-destructive X-ray fluorescence spectroscopy with a Rigaku ZSX Primus wavelength dispersive X-ray fluorescence spectrometer (ZSX Primus WD-XRF, The Woodland, TX, USA).

The instruments which were used for analysis of PM10 and PM2.5 mass were calibrated before analysis of the samples with traceable standards as per recommended standard procedures of the respective instruments [12].

3. Results and Discussion In the present analysis, we have tried to understand the impact of „odd-even scheme‟ on the concentration of pollutants of Delhi, India during Phase-I (1–15 January, 2016) and Phase-II (15–30 April, 2016) scheme. Ambient particulate matter (PM2.5 and PM10) and trace gases (NO, NO2 CO, SO2 and NH3) were measured before (2 weeks before the odd-even scheme), during (during the odd-even scheme) and after (2 weeks after the odd-even scheme) of the „odd-even scheme‟ at an urban site of Delhi. Variation of trace gases and chemical characteristics of particulate matter (PM2.5 and PM10) are described below.

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3.1 Phase-I

The average mixing ratios of ambient NOx, CO, SO2 and NH3 along with chemical characteristics of particulate matter (PM2.5 and PM10) before, during and after odd-even scheme (Phase-I: winter) at Delhi are summarized in Table 1 & 2(a, b). Before implementation of odd-even scheme (winter season), the mixing ratios of ambient NO x, CO, SO2 and NH3 were of the order of 47.06 ± 6.61 ppb, 1.78 ± 0.14 ppm, 1.97 ± 0.37 ppb and 25.90 ± 4.23 ppb, respectively, whereas, just after the completion of odd-even scheme, mixing ratio of trace gases (NOx= 49.22 ± 5.92 ppb, CO = 1.77 ± 0.13 ppm, SO2 = 2.22 ± 0.19 ppb and NH3=22.45 ± 3.37 ppb) registered even higher concentration than the same before implementation. Ofcourse, during the odd-even scheme, little reduction has been noticed in the average mixing ratios of NOx (47.06 ± 6.61 ppb (before) to 41.36 ± 6.09 ppb (during)), CO(1.78 ± 0.14 ppm (before) to 1.69 ± 0.27 ppm (during)), SO2 (1.97 ± 0.37 ppb (before) to 1.74 ± 0.28 ppb(during)) and NH3 (25.90 ± 4.23 ppb (before) to 15.16 ± 2.98 ppb(during)). Trace gases has followed the high-low-high pattern during the Phase-I. Daily average mixing ratios of ambient trace gases (NOx, CO, SO2 and NH3) before, during and after the odd-even scheme are depicted in Fig. 2. Sharma et al. [14] have also reported earlier the similar trend in the average mixing ratio of ambient NO (12.18 ± 4.66 ppb), NO2 (10.70 ± 3.25 ppb,), CO (1.66 ± 1.04 ppm) SO 2 (1.97 ± 0.85 ppb) and NH3 (20.23 ± 2.71 ppb) at the same observational site during winter 2008. Unlike the variation (high-low-high) in trace gases, average concentrations of PM2.5 (254.5 ± 82.5 µg m-3) and PM10 (339.4 ± 70.7 µg m-3) have reported reduction during (PM2.5: 220.9±77.8 µg m-3 and PM10: 324.8±96.8 µg m-3) and after (PM2.5: 208.5±31.8 µg m-3 and PM10: 283.7±43.3 µg m-3) the odd-even scheme (Fig. 3). Daily average concentrations of PM2.5 and PM10 before, during and after the odd-even scheme are also shown in Fig. 4. The reduction in concentrations of PM2.5 and PM10 accounts marginally by –13% and –5%, respectively when analysed the data before and after the implementation of odd-even scheme (Table 2 a). Although the mass concentrations of PM2.5 and PM10 were reduced marginally during odd-even scheme, however, the concentrations of PM2.5 and PM10 were even reported more than 3 times of the National Ambient Air Quality Standards (NAAQS: 60 µg m-3 for PM2.5 and 100 µg m-3 for PM10; 24 h average). Several studies on PM2.5 and PM10 concentrations over individual stations of Delhi are reported earlier [7, 14-18]. The highest concentration of PM2.5 and PM10 mass during the winter months (during Phase-I) than summer months over Delhi may be due to the combined effect of source strength, lower boundary layer height [19-20] and prevailing meteorological conditions at the observational site.

OC, EC, WSIC, trace elements and stable C&N isotopic compositions of PM2.5 and PM10 before, during and after the odd-even scheme at Delhi are summarized in Table 2a. Although the reduction of concentrations of PM 2.5 and PM10 accounts marginally by 13% and 5%, however, the reduction of concentrations of OC and EC of PM 2.5 mass were by 5% and 6%,. Similarly, concentration of OC and EC of PM 10 were also reduced by 3% and 4%, respectively. Potassium (K) is used as tracer of crustal dust in the coarse range and soluble K + for biomass burning in the fine range of PM [21]. Since, higher concentrations of K+ has been recorded, K+/OC and K+/EC ratios may be used to characterize the relative emission from biomass burning. The OC/EC, K+/OC, K+/EC and Cl–/EC ratios of

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PM2.5 and PM10 at the sampling site of Delhi are attributed to the combined effects of traffic emission and biomass burning during the study [22-23]. Slight reduction in EC concentration during odd-even scheme and OC/EC ratio of PM2.5 and PM10 might be the influence of reduction in vehicle exhaust in the city (Table 2a). The isotopic composition of C (δ13CTC) and N (δ15NTN) of aerosol are used as fingerprint to identify the source types of the aerosol. In the present study, average values of δ13CTC of PM2.5 and PM10 (before, during and after the scheme) were –25.0 ± 0.7‰ and –24.5 ± 0.8‰, respectively (Table 2a). This represents an intermediate value of aerosols emitted predominantly from biomass burning and fossil fuels combustion (diesel, petrol and coal). Delhi and Kolkata represent the influence of heavy road side traffic, and δ13CTC of PM10 was recorded as ~ –25.5‰ and ~ –25.9‰, respectively [11]. Nitrogen in ambient particulate matter (PM) is present mainly in the forms of nitrate (NO3-) and ammonium (NH4+). Roadside vehicles and industrial activities in urban areas also contribute N in particulates through oxidation of gaseous NOx (NO and NO2). The major N compound in particulates (ie., NH4NO3 and (NH4)2SO4) may be produced mainly through gas to particle conversion or a neutralization process of NH 3 gas with atmospheric acid gases, i.e., HNO3 and H2SO4 [24]. Hence, the addition of N to atmospheric particulates may involve complex chemical reactions, resulting in a very broad range of δ15NTN from –15 to + 30‰. In the present study, average values of δ15NTN of PM2.5 and PM10 were ranged from 7.7 ± 0.8‰ to 9.7 ± 0.5‰ (before, during and after the event) and expressed the source to be biomass burning, fossil fuel combustion and secondary aerosol (Table 2a).

Vehicular emission is generally dominated by EC, OC, Cu, Zn, Ba, Sb, Pb, Mn, Mo and Ni, which are widely used as markers of vehicle sources. In the present study, we are reporting the concentration of Cu, Zn, Mn, Pb, Ba, OC and EC in PM10 as indicator of vehicular emission (Table 2a). Furusjo et al. [25] suggested that high concentrations of Cu, Zn, Mn, Sb, Sn, Mo, Ba and Fe are markers of brake wear and can serve as indicators of traffic re-suspension [26]. In two-stroke engines, fuel and lubricant are mixed and burnt together in the piston chambers, with Zn being emitted. In a four-stroke engine, lubricants are introduced into the cylinders separately and Zn is emitted from the four stroke materials [27]. Internationally, EC [28] is used extensively as a marker for diesel exhaust.

In the present case, the concentration of vehicular marker elements (Cu, Zn, Mn, Pb, Ba, OC and EC in PM 10) were reduced marginally during the odd-even event indicating marginal effect of vehicular emission in Delhi.

3.2 Phase-II After completion of first phase „odd-even scheme‟ of private vehicles (cars), the transport authority of megacity Delhi initiated the second phase odd-even scheme during 15–30 April 2016 (Phase-II: summer). In the second phase, we have repeated similar type of experiments (trace gases and particulate matter) to measure the trace gases and PM2.5 and PM10 and compare with Phase-I results (although it is different season).

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During phase-II the mixing ratios of ambient NOx, CO, SO2 and NH3 were recorded as 38.46 ± 8.42 ppb, 2.77 ± 0.53 ppm, 2.22 ± 0.41 ppb and 20.11 ± 5.12 ppb, respectively before the odd-even scheme whereas, after the oddeven scheme it reported 39.18 ± 6.91 ppb, 2.23 ± 0.45 ppm, 2.42 ± 0.43 ppb and 16.42 ± 4.21 ppb, respectively. During the odd-even scheme, the average mixing ratios of NOx, CO, SO2 and NH3 were recorded as 32.59 ± 9.12 ppb, 2.10 ± 0.32 ppm, 2.17 ± 0.29 ppb and 12.07 ± 0.29 ppb, respectively (Table-1 and Fig.5). The mixing ratios of all the trace gases account reduction during odd-even scheme. After implementation of odd-even scheme, trace gases have shown reduction in concentration of trace gases, however, just after completion of the scheme, concentration of all trace gases have shoot up, particularly, NO x, which even crossed the concentration registered before the scheme. The effect of several activities of NCR region, i.e., just outside Delhi boundary could be reason for such variation (high-low-high) like phase-I. Unlike, Phase-I, chronologically average concentrations of PM2.5 (138.0±14.2 µg m-3 (before), 163.7 ± 20.7 µg m-3 (during) and 135.8±23.6 µg m-3 (after)) and PM10 (187.2±33.6 µg m-3 (before), 218.2 ± 44.6 µg m-3 (during) and 183.9±60.3 µg m-3 (after) show intriguing picture (Fig. 3 and Fig.4). The concentrations of PM 2.5 and PM10 were increased marginally by 18% and 16%, respectively when compared with before the odd-even event (Table 2b). Although, in Phase-II, the concentrations of PM2.5 and PM10 were recorded more than 2 times the National Ambient Air Quality Standards (NAAQS: 60 µg m-3 for PM2.5 and 100 µg m-3 for PM10; 24 h average), PM2.5 and PM10 have shown low-high-low pattern. Higher average concentrations of PM2.5 (163.7 ± 20.7 µg m-3) and PM10 (218.2 ± 44.6 µg m-3) were recorded during the odd-even scheme than before (PM2.5: 138.0±14.2 µg m-3 and PM10: 187.2±33.6 µg m-3) and after (PM2.5: 135.8±23.6 µg m-3 and PM10: 183.9±60.3 µg m-3) the odd-even scheme (Fig. 3). Daily average concentrations of PM2.5 and PM10 before, during and after the odd-even scheme are also shown in Fig. 4. The concentrations of PM 2.5 and PM10 were increased marginally by 18% and 16%, respectively when compared with before the odd-even event (Table 2 b). The concentrations of PM2.5 and PM10 were recorded more than 2 times the National Ambient Air Quality Standards (NAAQS: 60 µg m-3 for PM2.5 and 100 µg m-3 for PM10; 24 h average) during phase-II scheme. OC, EC, WSIC, trace elements and stable C&N isotopic compositions of PM 2.5 and PM10 before, during and after of odd-even scheme at Delhi are summarized in Table 2b. The concentrations of OC and EC of PM 2.5 mass were increased by 23% and 15%, respectively when compared with 2 weeks before the implementation of odd-even scheme. Similarly, concentration of OC and EC of PM10 were also increased by 31% and 18%, respectively. The OC/EC ratio of PM2.5 and PM10 at the sampling site of Delhi is attributed to the influence of traffic exhaust during the study [11, 18]. During odd-even scheme, the concentration of OC and EC of PM2.5 and PM10 slightly increased may be due to meteorological condition of the sampling site (Table 2b). During phase-II, the average values of δ13CTC of PM2.5 and PM10 (before, during and after) were –26.4 ± 1.8‰ and –26.0 ± 0.6‰, respectively (Table 2b). The isotopic value of δ13CTC represents the aerosols emitted from

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predominantly fossil fuels combustion (diesel, petrol and coal etc.). In the present study, average values of δ15NTN of PM2.5 and PM10 were ranged from 4.4± 1.2‰ to 13.7 ± 0.5‰ (before, during and after the event) and expressed the source to be fossil fuel combustion (mainly diesel and coal) and secondary aerosol (Table 2b). Sharma et al. [11] also reported the similar results during the summer season of 2010 at the same sampling site.

The concentrations of marker elements in PM10 samples (Cu, Zn, Mn, Pb and Ba) were decreased during the odd-even scheme (Table 2b) suggesting the reduction in vehicle exhaust. The higher concentrations of Al, Cl, Fe, Zn, Cr and SO42- at the sampling site clearly indicate the source of fossil fuel combustion of PM 10 mass. The concentrations of marker elements of fossil fuel combustion were also reduced slightly during the odd-even scheme.

3.3 Analysis of Air Mass back Trajectories

In order to identify the possible transport pathways of PM 2.5 and PM10 from their potential sources of origins to Delhi, 5 days backward trajectory calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model have been traced [29]. Air mass back-trajectories for each experimental day for 500 m above the ground level (AGL) during 16 December 2015 to 31 January 2016 (for phase-I) and 1 April 2016 to 15 May 2016 (for phase-II) have been calculated using GDAS meteorological data (http://www.arl.noaa.gov). HYSPLIT was run every day starting at 0500 h, UTC (Universal Time Coordinated), at a starting height of 500 m AGL on an hourly basis. Figure 6a&b shows the HYSPLIT air mass parcel from long range transport at the receptor site during phaseI and phase-II of odd-even event. During phase-I (winter), the approaching air mass at the receptor site is mainly of continental type and transported from the northern IGP (Punjab, Haryana and northern Uttar Pradesh) and its surrounding areas. During phase-II of odd-even event (summer), the approaching air mass at the receptor site is mainly from Rajasthan (Thar desert), Gujarat and IGP. Sharma et al. [18] had also observed the similar trajectories at Delhi during winter and summer 2010.

4.

Conclusions

Based on earlier reports that transport sector contributes 10-30 % to PM2.5 and PM10, the state Government adopted “Odd-Even Scheme” to improve the air quality of Delhi. Odd-even scheme in both the phases have shown mixed results in trace gases and particulate matter. The mixing ratios of trace gases during both phases have shown high-low-high pattern giving momentary effect of odd-even scheme, whereas, concentrations of PM2.5 and PM10 and their chemical constituents have shown completely different patterns during two phases. The marker elements and isotopic analysis of (C and N) of PM2.5 and PM10 samples indicated that vehicle exhaust are one of the major sources of PM2.5 and PM10 at the sampling site of Delhi. Previous studies reported the presence of other sources (soil dust, secondary aerosol, biomass burning and fossil fuel combustion etc) of PM 2.5 and PM10 which influence the ambient air quality of Delhi. Since meteorology plays a major role in distributing pollutants, role of sources in deriving the

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seasonal variation of pollutant over Delhi should be characterized. In the present two cases, duration of the scheme was too short to understand role of different sources applying established models.

Acknowledgments Authors are thankful to the Director, CSIR- NPL, New Delhi and Head, Environmental Sciences and Biomedical Metrology Division, CSIR-NPL, New Delhi, India for their constant encouragement and support. The present work has been carried out under the CSIR-NPL Mission Mode project (Project code: MP-3a). The authors are thankful to the anonymous reviewer and editor for their constructive suggestions to improve the manuscript.

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Table 1 Average mixing ratios of ambient trace gases before, during and after odd-even scheme. _____________________________________________________________________________ Parameters Before During After ______________________________________________________________________________ Phase I (1–15 January, 2016) NOx (ppb) 47.06 ± 6.61 41.36 ± 6.09 49.92 ± 5.92 CO (ppm) 1.78 ± 0.14 1.69 ± 0.27 1.77 ± 0.13 SO2 (ppb) 1.97 ± 0.37 1.74 ± 0.28 2.22 ± 0.19 NH3 (ppb) 25.90 ± 4.23 15.16 ± 2.98 22.45 ± 3.37 ________________________________________________________ Phase II (15–30 April, 2016) NOx (ppb) 38.46 ± 8.42 32.59 ± 9.12 39.18 ± 6.91 CO (ppm) 2.77 ± 0.53 2.10 ± 0.32 2.23 ± 0.45 SO2 (ppb) 2.22 ± 0.41 2.17 ± 0.29 2.42 ± 0.43 NH3 (ppb) 20.11 ± 5.12 12.07 ± 4.18 16.42 ± 4.21 ________________________________________________________________________________

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Table 2a: Concentrations of chemical constituents (in µg m-3) of PM2.5 and PM10 befere, during and after 1st Phase odd-even strategy ____________________________________________________________________________________________________________________ PM2.5 PM10 _________________________________________ ____________________________________________ Parameters Before During After Before During After ____________________________________________________________________________________________________________________ Mass 254.5 ± 82.5 220.9 ± 77.8 208.5 ± 31.8 339.4 ± 70.7 324.8 ± 96.8 283.7 ± 43.3 OC 29.3 ± 9.2 27.8 ± 6.1 28.8 ± 2.6 50.0 ± 9.5 48.4 ± 7.3 41.9 ± 7.5 EC 12.4 ± 2.1 11.6 ± 1.1 15.4 ± 1.6 15.3 ± 6.6 14.7 ± 2.6 14.9 ± 3.6 TC 41.7 ± 6.3 39.4 ± 3.6 34.2 ± 3.1 65.3 ± 6.9 63.1 ± 5.2 56.8 ± 4.3 TN 31.5 ± 6.4 33.8 ± 4.2 26.4 ± 7.6 61.1 ± 8.4 63.8 ± 13.1 51.7 ± 8.1 13 δ CTC –24.9 ± 0.4 –25.0 ± 0.7 –25.1 ± 0.7 –24.4 ± 0.6 –24.4 ± 0.8 –24.6 ± 0.6 δ15NTN 7.7 ± 0.8 8.5 ± 0.4 9.7 ± 0.5 8.7 ± 0.6 8.3 ± 0.5 8.0 ± 0.4 Cl– 6.3 ± 3.6 5.9 ± 4.5 5.2 ± 2.2 8.9 ± 3.2 6.3 ± 5.4 7.4 ± 4.2 2– SO4 19.7 ± 3.0 24.3 ± 6.7 17.0 ± 4.6 27.4 ± 2.8 28.9 ± 8.2 19.1 ± 6.5 NO3– 23.7 ± 3.4 22.4 ± 5.9 21.6 ± 4.5 37.7 ± 4.9 35.0 ± 3.2 25.7 ± 4.3 NH4+ 8.3 ± 1.7 7.1 ± 1.8 8.6 ± 2.3 18.3 ± 4.2 15.9 ± 7.4 14.7 ± 3.7 + Na 4.6 ± 0.8 3.4 ± 1.6 4.2 ± 2.3 5.1 ± 0.9 4.3 ± 3.1 6.2 ± 2.4 K+ 5.8 ± 1.5 4.9 ± 2.1 4.9 ± 1.5 8.5 ± 2.3 7.9 ± 5.4 9.9 ± 5.8 Mg2+ 1.3 ± 0.8 1.2 ± 0.5 1.1 ± 0.7 1.6 ± 0.5 1.1 ± 0.8 1.2 ± 0.4 Ca2+ 7.1 ± 1.5 6.9 ± 2.8 6.5 ± 2.5 10.9 ± 1.9 7.0 ± 1.6 14.2 ± 2.5 Ba – – – 5.63 ± 0.67 4.63 ± 0.33 6.18 ± 0.57 Al – – – 3.44 ± 0.69 2.96 ± 2.10 2.50 ± 1.33 P – – – 0.19 ± 0.02 0.13 ± 0.11 0.10 ± 0.03 S – – – 4.81 ± 1.10 5.83 ± 1.73 5.61 ± 1.08 Ti – – – 0.06 ± 0.02 0.04 ± 0.03 0.03 ± 0.02 Fe – – – 0.27 ± 0.07 0.16 ± 0.11 0.12 ± 0.05 Zn – – – 0.21 ± 0.13 0.21 ± 0.06 0.18 ± 0.01 Cu – – – 0.08 ± 0.01 0.06 ± 0.01 0.07 ± 0.01 Mn – – – 0.03 ± 0.01 0.02 ± 0.01 0.01 ± 0.01 Cr – – – 0.04 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 Br – – – 0.02 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 Pb – – – 0.01 ± 0.002 0.01 ± 0.002 0.01 ± 0.003 ___________________________________________________________________________________________________________________ ± Standard deviation

14

Table 2b: Concentrations of chemical constituents (in µg m-3) of PM2.5 and PM10 befere, during and after 2nd Phase odd-even strategy ___________________________________________________________________________________________________________________ PM2.5 PM10 ___________________________________________ ___________________________________________ Parameters Before During After Before During After ___________________________________________________________________________________________________________________ Mass 138.0 ± 14.2 163.7 ± 20.7 135.8 ± 23.6 187.2 ± 33.6 218.2 ± 44.6 183.9 ± 60.3 OC 10.6 ± 2.9 13.1 ± 6.0 9.6 ± 1.2 20.3 ± 3.2 26.7 ± 7.2 25.1 ± 5.3 EC 4.6 ± 1.5 5.3 ± 1.9 3.9 ± 1.4 6.2 ± 1.6 7.3 ± 2.7 3.9 ± 1.2 TC 15.2 ± 2.3 18.4 ± 3.2 13.5 ± 1.3 26.5 ± 2.7 34.0 ± 5.1 29.0 ± 3.2 TN 12.1 ± 1.2 11.2 ± 2.1 15.5 ± 1.2 28.1 ± 1.5 23.8 ± 3.4 35.9 ± 3.8 δ13CTC –26.1 ± 0.2 –26.6 ± 0.3 –26.5 ± 0.4 –26.2 ± 0.5 –26.2 ± 0.8 –25.7 ± 0.5 15 δ NTN 6.1 ± 0.4 5.9 ± 1.8 4.4 ± 0.7 11.3 ± 2.5 13.7 ± 2.3 11.7 ± 3.6 Cl– 4.5 ± 2.9 4.7 ± 2.0 4.8 ± 2.6 5.5 ± 6.2 5.1 ± 5.2 7.3 ± 5.8 SO42– 9.5 ± 3.3 7.3 ± 3.0 10.8 ± 4.8 13.7 ± 5.5 12.5 ± 6.2 14.5 ± 7.3 – NO3 7.8 ± 2.6 4.2 ± 2.9 6.2 ± 1.2 17.5 ± 7.2 18.5 ± 8.6 18.3 ± 3.6 NH4+ 5.6 ± 2.2 2.8 ± 1.6 3.5 ± 1.3 6.4 ± 4.7 4.2 ± 2.9 5.8 ± 4.1 Na+ 3.8 ± 1.0 3.5 ± 2.8 3.7 ± 1.9 5.5 ± 2.4 3.1 ± 1.8 4.4 ± 2.0 K+ 2.8 ± 1.4 2.9 ± 1.8 4.3 ± 2.5 7.2 ± 5.5 5.3 ± 3.1 6.0 ± 3.0 2+ Mg 0.5 ± 0.2 1.4 ± 1.0 0.7 ± 0.5 1.1 ± 0.6 2.0 ± 1.4 1.5 ± 0.7 Ca2+ 5.8 ± 1.4 6.4 ± 1.3 5.6 ± 1.6 7.2 ± 3.4 6.5 ± 4.4 5.1 ± 3.4 Ba – – – 4.09 ± 1.02 2.95 ± 0.67 4.35 ± 0.20 Al – – – 3.02 ± 0.90 4.56 ± 0.64 2.86 ± 0.36 P – – – 0.15 ± 0.03 0.17 ± 0.04 0.16 ± 0.01 S – – – 1.96 ± 0.85 1.82 ± 0.24 2.06 ± 0.91 Ti – – – 0.06 ± 0.01 0.06 ± 0.02 0.08 ± 0.05 Fe – – – 0.21 ± 0.06 0.22 ± 0.06 0.12 ± 0.05 Zn – – – 0.13 ± 0.09 0.09 ± 0.05 0.07 ± 0.02 Cu – – – 0.03 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 Mn – – – 0.01 ± 0.01 0.01 ± 0.01 0.01 ± 0.01 Cr – – – 0.02 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 Br – – – 0.01 ± 0.01 0.01 ± 0.01 0.02 ± 0.01 Pb – – – 0.01 ± 0.004 0.01 ± 0.004 0.01 ± 0.002 ___________________________________________________________________________________________________________________ ± Standard deviation

15

`

, 77.171969)

Fig.1. Map of sampling location.

16

Before

During

After

Fig. 2. Mixing ratios of ambient NOx, CO, SO2 and NH3 before, during and after odd-even scheme (Phase-I).

17

Fig. 3. Concentration of PM2.5 and PM10 before, during and after odd-even scheme

18

Before

During

After

Before

During

After

Fig. 4. Concentration of PM2.5 and PM10 before, during and after odd-even scheme

19

Before

During

After

Fig. 5. Mixing ratios of ambient NOx, CO, SO2 and NH3 before, during and after odd-even scheme (Phase-II)

20

(a)

(b)

Fig. 6a. Air parcel back trajectories a) before, b) during and c) after the odd-even event (Phase-I)

21

(c)

(a)

(b)

Fig. 6b. Air parcel back trajectories a) before, b) during and c) after the odd-even event (Phase-II)

22

(c)