Black carbon linked aerosol hygroscopic growth: Size and mixing state are crucial

Accepted Manuscript Black Carbon Linked Aerosol Hygroscopic Growth: Size and Mixing State are Crucial Bighnaraj Sarangi, S. Ramachandran, T.A. Rajesh, Vishnu Kumar Dhaker PII:

S1352-2310(18)30846-X

DOI:

https://doi.org/10.1016/j.atmosenv.2018.12.001

Reference:

AEA 16428

To appear in:

Atmospheric Environment

Received Date: 17 August 2018 Revised Date:

20 November 2018

Accepted Date: 5 December 2018

Please cite this article as: Sarangi, B., S., T.A., Dhaker, V.K., Black Carbon Linked Aerosol Hygroscopic Growth: Size and Mixing State are Crucial, Atmospheric Environment, https://doi.org/10.1016/ j.atmosenv.2018.12.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

1

MANUSCRIPT Black Carbon Linked ACCEPTED Aerosol Hygroscopic Growth: Size and Mixing

2

State are Crucial

3

Bighnaraj Sarangi, S. Ramachandran, T. A. Rajesh and Vishnu Kumar Dhaker

4 5

Space and Atmospheric Sciences Division, Physical Research Laboratory, Ahmedabad-380009, India

6

(*Corresponding author: [email protected]) ABSTRACT

RI PT

7

The objective of this study is to characterise urban refractory black carbon (rBC)

9

mixing state relative to hygroscopic growth factor (HGF) of size selective aerosols to better

10

constrain the aerosol indirect effect. The Aitken mode range (≤ 100 nm) is dominated by

11

particles that have relatively low hygroscopicity and comprised freshly emitted hydrophobic

12

rBC, however, our observations suggest that BC mixing states in Aitken range ( down to 70

13

nm) still govern the hygroscopic properties. Conversely, the accumulation mode range (> 100

14

nm) dominated by particles that have relatively high hygroscopicity consisted of oxidized

15

organic compounds and inorganic salts. Single particle soot photometer (SP2) measurement

16

further revealed that particles at lower size are mostly incandescent type dominated by

17

refractory component whereas higher size particles are mostly scattering type dominated by

18

nonrefractory component. The lower hygroscopicity parameter (κ) (0.26±0.08) obtained for

19

Aitken mode particles suggest that they may contain levoglucosan and levoglucosan-OH

20

oxidation products, and are possibly from biomass burning sources whereas accumulation

21

range particles with higher κ value (0.39±0.03) have ammonium sulfate, ammonium bisulfate

22

and malonic acid in their composition and their possible source would be secondary in origin.

23

These findings are important because for the first time, BC mixing state and the impact of

24

size selective rBC on HGF are determined directly over an urban region which have

25

implications to precipitation.

AC C

EP

TE D

M AN U

SC

8

26

ACCEPTED MANUSCRIPT

1. Introduction

Atmospheric aerosol uptakes water and grow in size with increasing relative humidity

28

(RH). This increment depends on the type of materials that constitute the aerosol. Evidently,

29

water soluble materials are highly responsible for the growth of the particles and thereby

30

changing the refractive index and hence aerosol optical properties (Charlson et al., 1992).

31

Aerosol particles under the influence of hygroscopic growth process get activated to cloud

32

condensation nuclei (CCN), thereby playing a crucial role in affecting the formation,

33

longevity, and albedo of clouds (Yuan et al., 2008; Wang et al., 2011), and give rise to aerosol

34

indirect effect. The hygroscopicity parameter depends on the chemical composition of the

35

aerosols (hydrophilic or hydrophobic) (Petters and Kreidenweis, 2007). To better constrain

36

the climate models, cloud resolving models and global climate simulation, accurate

37

quantification of aerosol hygroscopicity is needed so that aerosol-CCN activation process can

38

be parameterised (Chung and Seinfeld, 2002; Liu et al., 2005; Koch, 2011) better. Köhler

39

theory revealed that prediction of CCN formation depends upon the physico-chemical

40

properties i.e., composition, density, surface tension, activity coefficient of aerosols (Köhler,

41

1936).

M AN U

SC

RI PT

27

In general, aerosol particles are complex in nature because their size and composition

43

change with time and space. Earlier studies have inferred that inorganic compounds mostly

44

hydrophilic in nature contribute to hygroscopic growth of aerosol (Aggarwal et al., 2007).

45

Therefore, aerosol inorganic components are considered ubiquitous and effectively modelled

46

using Köhler theory. Nowadays, this theory has been extended to organics because

47

atmospheric aerosol is composed of both the components (Murphy et al., 1998). It is observed

48

that organic compounds constitute a major fraction of the aerosol particles in the atmosphere

49

(20-90%) (Zhang et al., 2007; Jimenez et al., 2009) and contribute to the hygroscopic growth

50

of the particles (Kiss et al., 2005). However, aerosol hygroscopic growth and CCN activation

51

are significantly perturbed by nonhygroscopic aerosol components such as black carbon (BC)

AC C

EP

TE D

42

2

ACCEPTED MANUSCRIPT

or elemental carbon (EC). BC is a strong radiation absorbing component of atmospheric

53

aerosols (Wang et al., 2013) and are primarily emitted from incomplete combustion of fossil

54

fuel and other sources e.g., biomass burning, vehicular emission, etc. Both ground based and

55

satellite observations revealed that the global solar absorption of BC is as large as 0.9 Wm-2

56

(Jacobson, 2001). Presence of BC can alter the aerosol characteristics e.g., size, mass, density,

57

optical and hygroscopic properties. Pure BC is hydrophobic in nature and its mixing state

58

with the hydrophilic components regulate the longevity of BC in the atmosphere (Peng et al.,

59

2017). It has been observed that BC coated with hydrophilic components (e.g., sodium

60

chloride, ammonium sulfate, ammonium nitrate, etc) increases the hygroscopic growth factor

61

whereas uncoated BC of externally mixed type may perturb the hygroscopicity and hence the

62

CCN activation (Moteki et al., 2004; Guo et al., 2016). This leads to uncertainties in

63

predicting CCN activation process because of insufficient knowledge on the mixing state of

64

BC. Atmospheric measurements have been performed to evaluate the aerosol in association

65

with climate relevant properties i.e., hygroscopicity, optical properties, CCN activities, etc,

66

with respect to aerosol mixing state (Zelenyuk et al., 2010; Hersey et al., 2013; Willis et al.,

67

2016). However, it is still challenging to study the influence of aerosol mixing state on

68

aerosol hygroscopic growth quantitatively because of the variability of aerosol mixing state

69

(i.e., from internal to external mixing state and vice versa) under ambient atmospheric

70

conditions. Further, it is difficult to input the aerosol hygroscopic growth in most global

71

climate model simulations. Therefore most of the global climate models assume single

72

mixing state for aerosols either externally mixed (Lohmann and Hoose, 2009; Jacobson,

73

2011) or internally mixed (Ghan and Zaveri, 2007), which are easy to incorporate from a

74

computational perspective but results in uncertainties while determining the aerosol effects on

75

climate. Till date, most of the studies were involved in quantification of nonrefractory (i.e.,

76

inorganics and organics, mostly hydrophilic components) bulk aerosol to predict particle

AC C

EP

TE D

M AN U

SC

RI PT

52

3

ACCEPTED MANUSCRIPT

77

hygroscopicity (Gysel et al., 2007; Hersey et al., 2009; Wu et al., 2013; Levin et al., 2014).

78

However, extensive investigation is needed for hydrophobic component especially the BC

79

mixing state in size selective aerosol under atmospheric condition. Further, information of

80

size selective BC aerosol and its influence on size resolved aerosol hygroscopic growth is

81

very much necessary to constrain aerosol-climate indirect effect. In this study, for the first time, we measured hygroscopic growth of size selective

83

atmospheric aerosols, quantify the aerosol BC content, and its mixing state at a single particle

84

level in an urban location. Results obtained from detailed analysis of size resolved particle

85

BC mixing state and its influence over hygroscopic growth are presented.

86 87 88

2. Experimental Methods

89

2.1. Measurement site and experimental setup

SC

RI PT

82

The measurement site is located at Physical Research Laboratory, Ahmedabad and the

91

measurement was done for five days (13th to 17th February, 2018) consecutively (Fig 1).

92

Ahmedabad has a hot, semi-arid climate with less rainfall and the climate is extremely dry.

93

The meteorological parameters such as temperature (ᵒC), relative humidity (RH, %), wind

94

speed (m s-1) and wind direction (degree) were recorded for the period discussed. The month

95

of February corresponds to the end of winter season in Ahmedabad when the surface wind is

96

calm and north/northeasterly. The aerosol over the site is associated with the air mass from

97

land only during winter. This provides a unique opportunity to investigate the mixing

98

characteristics of BC because of significant anthropogenic aerosol loading at the site. The

99

detailed synoptic surface wind pattern and HYSPLIT air mass trajectory are shown in Fig.

100

2(a) and 2(b). The average temperature, RH and wind speed recorded for the study period are

101

23.9±1.5ᵒC, 40.7±7.1%, and 1±0.1 ms-1, respectively (The meteorological data were accessed

102

from

TE D

M AN U

90

AC C

EP

https://app.cpcbccr.com/ccr/#/caaqm-dashboard-all/caaqm-

4

ACCEPTED MANUSCRIPT

landing/data/%7B%22state%22:%22Gujarat%22,%22city%22:%22Ahmedabad%22,%22stati

104

on%22:%22site_308%22%7D). The sampling location (23ᵒ02’09”N, 72ᵒ32’34”E) is

105

surrounded by vegetation, roadway traffic, and residential accommodation (left panel in Fig.

106

1). It can therefore be considered as the representative site of mixed source influence, such as

107

biogenic, residential, vehicular emissions, etc. The sampling setup comprised humidified

108

tandem differential mobility analyzer (HTDMA, Model 1040XP, MSP®) and a single particle

109

soot photometer (SP2, Droplet Measurement Technologies) (right panel in Fig. 1).

110 111

2.2. Humidified Tandem Differential Mobility Analyzer (HTDMA)

RI PT

103

HTDMA consists of differential mobility analyzer (DMA1), a nonradioactive

113

neutralizer (i.e., electrical ionizer), a high accuracy humidification conditioner, and a

114

scanning mobility particle sizer (SMPS: DMA2 + CPC (condensation particle counter,

115

butanol based)). Polydisperse aerosols were dried (<5% RH), neutralised and then classified

116

by electrical mobility inside DMA1 (right panel in Fig. 1). DMA1 segregates the size

117

selective (e.g., 70, 100, 200 and 300 nm) monodisperse aerosol (Shimada et al., 2005; Sarangi

118

et al., 2017) from polydisperse aerosols assuming the particles are spherical. DMA1 was

119

operated with a flow rate of 0.33 L min-1 and the sheath flow rate at 3.3 L min-1. The ratio of

120

sheath flow rate to sample aerosol flow rate was kept at 10:1 to get better size resolution from

121

the DMA1 (Sarangi et al., 2017). The monodisperse aerosols are then introduced into

122

humidity conditioner, where humidity was controlled at three different RH of 40, 65 and

123

90%, respectively. The three RH values selected have atmospheric relevance (i.e.,

124

representative RH values observed in winter, summer and monsoon) to better quantify

125

hygroscopic properties of the atmospheric aerosols at the site (Deshpande et al., 2010;

126

Ramachandran et al., 2012). The RH below 40% was not considered because aerosol

127

undergoes restructuring and does not show significant growth under humidification (Boreddy

AC C

EP

TE D

M AN U

SC

112

5

ACCEPTED MANUSCRIPT

and Kawamura, 2016). The humidity conditioner contains two nafion membrane humidifier

129

tubes connected in series placed on a metal plate attached to DMA2. The aerosol flow

130

circulates in the interior of the membranes whereas DMA2 sheath air circulates outside of the

131

membrane. The connection between nafion tubes and the DMA2 casing, and the sheath flow

132

circulation enabled minimization of thermal gradients and ensured uniform temperature of

133

both the flow systems (i.e. aerosol and sheath air). Two RH sensors are used in the sheath

134

flow loop. A capacitive sensor is further used to control the RH accurately after a set point

135

has been entered. After humidification/dehumidification, the aerosol particle size distributions

136

are measured using SMPS operated at a flow rate 0.3 L min-1 (refer to F-T1 in Supplementary

137

information). DMAs within HTDMA were calibrated using polystyrene latex (PSL) spheres

138

of 101.8 nm (SRM 1963a) and 269 nm (SRM 1691) diameter traceable to national institute of

139

standards and technology (NIST). Once both the DMAs are calibrated with the reference

140

PSL, then dried (below 5% RH) particle of different size interest are selected at DMA1 and

141

the corresponding sizes were measured with DMA2 at RH below 5%. This gives the sizing

142

performance of both the DMAs. In this study, we have selected atmospheric particle of sizes

143

70, 100, 200 and 300 nm respectively using DMA1 and measured correctly the dried size at

144

DMA2.

145

2.3. Hygroscopic Growth Factor (HGF) Measurement

M AN U

SC

RI PT

128

Atmospheric aerosol particles are directly aspirated and dried using nafion dryer. To

147

measure the HGF of size selective atmospheric aerosols, we selected Aitken (70 and 100 nm)

148

and accumulation (200 and 300 nm) range particles using DMA1 as particles in these size

149

ranges are climatically relevant and highly susceptible to CCN formation (Laaksonen et al.,

150

2005). The particle sizes are further measured by DMA2 after humidification at different

151

humidity conditions (i.e., 40, 65 and 90% RH). The HGF (g(RH)) of an aerosol is defined as

AC C

EP

TE D

146

6

ACCEPTED MANUSCRIPT

152

the ratio of particle diameter at certain elevated RH to the initial dry diameter of the particle,

153

which can be expressed as =

154



=

(1)

155

where,

is the initial dry diameter of the particles at < 5% RH.

156

diameter measured at a set elevated RH.

is the humidified

For validation purposes, the g(RH) of pure NaCl particles were measured

158

(https://www.mspcorp.com/resources/msp-pi-1040xp-rev-a-model-1040xp-htdma.pdf) using

159

HTDMA and compared with the theoretical growth factor. The measured growth factor of

160

NaCl particles showed good agreement with the theoretical growth factor between 10 and

161

93% RH.

162

2.4. Hygroscopicity parameter (κ)

SC

RI PT

157

κ is defined to link the particle dry diameter to its cloud condensation nuclei (CCN)

164

activation process. κ measures the hygroscopicity of the particles based on Köhler theory

165

(Petters and Kreidenweis, 2007) and is a function of chemical species that constitute the

166

aerosol. In general, κ values are between 0 (nonhygroscopic species) and ~1.4 (hygroscopic

167

species) (Boreddy and Kawamura, 2016). Most of the studies revealed that atmospheric

168

aerosol is typically characterized by 0.1< κ <0.9 (Petters and Kreidenweis, 2007). The

169

hygroscopicity parameter (κ) can be calculated using following equation (Boreddy and

170

Kawamura, 2016),

174

TE D

173



(2)

where g(RH) is the calculated HGF and aw is the water activity = with

×

!

EP

172

=

AC C

171

M AN U

163

7

(3)

ACCEPTED MANUSCRIPT (4)

#$/& ×'

175

" =

176

where *+/ is the surface tension (71.99 mN m-1 at 25 ᵒC) at solution-air interface, , is the

177

molecular weight (18 g mol-1) of water, -

178

universal gas constant, T is the temperature in Kelvin, and D0 is the particle diameter.

(

)

is the density (1 g cm-3) of water, R is the

179 180

2.5. Single Particle Soot Photometer (SP2) SP2 was placed downstream of DMA1 and part of the monodisperse flow received by

182

SP2 operated at flow rate 0.03 L min-1. It should be noted that both the DMA2 and SP2 were

183

placed at the downstream of the DMA1 and run at two different flow rates. Both DMA2 and

184

SP2 are equipped with mass flow controllers. In our observation, we found negligible

185

deviation in sample flow rate when both DMA2 and SP2 were run at two different flow rates

186

simultaneously. The detailed principle and working methodology of SP2 have been discussed

187

elsewhere (Stephens et al., 2003; Baumgardner et al., 2004). In brief, SP2 consists of an air

188

jet inlet for monodisperse flow of particles which intersects an intense (~1 MW cm-2)

189

continuous laser (Nd: YAG) beam (Gaussian distribution, ~ 1 mm width) having wavelength

190

1064 nm pumped by a diode laser. Four detectors (avalanche photo-detector (APD)) are

191

positioned to capture light scattered by particles at a solid angle (~90˚sr) of the laser beam.

192

All the APDs are optically filtered to detect the scattered radiation from the particles at

193

different wavelength bands. Two of the detectors sense the Gaussian response scattered

194

radiation at a wavelength band of ~ 1064 nm at two different gain settings that are used to

195

optically size nonrefractory aerosols which are of scattering type. The two other detectors

196

sense the incandescence radiation (nonGaussian) which is either a broadband (490-700 nm)

197

or narrowband (630-700 nm) from the particles at its sublimation point (mostly refractory

198

components, essentially black carbon (BC)). It should be noted that all particles scatter light

199

and only black carbon (BC) containing particles absorb and incandesce. Therefore, SP2 is

AC C

EP

TE D

M AN U

SC

RI PT

181

8

ACCEPTED MANUSCRIPT

capable of measuring both scattering and incandescence mass and size distributions of

201

aerosol, and accurately quantifies the mixing state of BC at a single particle level. A proper

202

optical alignment of SP2 laser and particle beam with respect to an optimal position of each

203

detector is essential to ensure all the particles pass through the beam maxima, so that accurate

204

determination of scattering and incandescence signals can be done (Schwarz et al., 2006).

205

Calibration of scattering channel of SP2 was done using PSL-200 nm sphere traceable to

206

NIST and calibration of incandescence channel was done using DMA sized aquadag particles

207

of known density of 1.80 g cm-3. The detailed BC mass and size calibration procedure

208

followed for SP2 is given in Baumgardner et al.(2012). It is important to note that SP2

209

measures black carbon that is referred to as refractory BC (rBC) where the term ‘refractory’ is

210

used based on the measurement technique only. Hence, rBC concentrations measured in this

211

study can be compared with the BC concentrations reported elsewhere using other techniques.

SC

RI PT

200

212 213

3. Results and discussion

215

M AN U

214

3.1. Hygroscopic Growth Factor (HGF)

Humidified particle size distributions measured using SMPS for atmospheric aerosols

217

(i.e., selected dry (<5% RH) size at 70, 100, 200 and 300 nm). The apparent shifting of mode

218

size distributions for 100 nm particles observed under different relative humidity (40, 65 and

219

90% RH) condition is shown in the left panel of Fig. 3. The size mode shifted a little towards

220

higher size (i.e., size increment range between 0.33 and 7.3%) when RH increases from 40 to

221

65%, whereas the mode diameter shifted to higher size (i.e., size increment range between

222

13.3 and 63.8%) significantly when RH increases from 65 to 90%. This is because

223

hygroscopic chemical constituents readily get activated at 90% RH. Apart from this, our

224

observation revealed that most of the humidified size distributions especially for higher (e.g.,

AC C

EP

TE D

216

9

ACCEPTED MANUSCRIPT

200 and 300 nm) size particles at 90% RH are bimodal in nature as shown in the right side

226

upper panel of Fig. 3. The bimodal distributions for higher size particles at 90% RH arise

227

possibly due to mixing state of the particles. HGF is calculated using eq.1 for all particle

228

sizes at different RH conditions. The measured HGF at 90% RH is lower (1.39±0.13) for

229

Aitken mode size (≤ 100 nm) particles whereas it is higher (1.6±0.02) for accumulation mode

230

size (> 100 nm) particles. This difference in HGF with respect to particle size is attributed to

231

particle mixing state (Laskina et al., 2015). This occurs because when mixing states differ it

232

will result in varied humidified sizes and different hygroscopic properties. In general,

233

atmospheric aerosols are multicomponent (homogeneously mixed or phase separated)

234

particles leading to different water uptake properties. In this study, we observed water uptake

235

properties of aerosol is size dependent as accumulation size range particles show high HGF

236

than the Aitken size range particles. However, our observations suggest that BC mixing states

237

in Aitken range (down to 70 nm) still govern the hygroscopic properties. The observed mean

238

hygroscopic growth factors (HGFs) for the period February 13 - 17, 2018 calculated within

239

the size range 70 to 300 nm are 1.08±2, 1.09±2, and 1.54±1 for relative humidity of 40%,

240

65%, and 90% respectively. The measured HGF at subsaturated (i.e., 90% RH) is close to the

241

HGF (1.58) reported over Indian Ocean (Sheridan et al., 2002). The measured mean HGF

242

increases with the increase in RH and agreed well with the HGF obtained earlier using

243

Optical Properties of Aerosols and Clouds (OPAC) model (Ramachandran et al., 2012) over

244

an urban region.

246

SC

M AN U

TE D

245

RI PT

225

3.2. Refractory black carbon and mixing state

The mean rBC mass concentration from SP2 is found to be 11.39±6.37µg m-3 in the

248

size range of 70-300 nm. The observed rBC mass concentration is much higher compared to

249

rBC concentrations reported from Ahmedabad (3.86±2.82 µg m-3 in 2004 and 10.02±5.69 µg

AC C

EP

247

10

ACCEPTED MANUSCRIPT

250

m-3 in 2005), and is higher than that measured over western, and central India

251

(Ramachandran, and Rajesh, 2007).

252

concentration increases as particle size increases (Fig. 4(a)). The average rBC mass

253

concentrations obtained for particles of size 70, 100, 200 and 300 nm are respectively

254

0.02±0.01, 0.24±0.2, 5.17±3.5, and 5.96±3 µg m-3. The measurement is done in ascending

255

order with respect to size from smaller to higher size i.e., 70, 100, 200 and 300 nm (refer to S-

256

T1 in Supplementary information). In our observation, most of rBC mass concentrations

257

show similar trend with respect to their size (i.e., 70 to 200 nm) on consecutive measurement

258

dates (Fig. 4(b)) except for particles of size 300 nm. Particles of size 300 nm have different

259

rBC mass concentration trend because most of the measurements performed in this size are in

260

the afternoon (17:00 local time (LT)) when anthropogenic activities, especially, vehicular

261

emissions increase over the measurement location with respect to afternoon (Rajesh and

262

Ramachandran, 2017).

SC

RI PT

Further, it has been observed that rBC mass

rBC mixing state can be determined from the observed scattering (mostly resulted

264

from nonrefractory aerosol) and incandescence (only resulted from refractory black carbon)

265

signals that are obtained from SP2 as a result of interaction of Nd: YAG laser beam with the

266

DMA sized particles. SP2 measurement provides single particle information such as

267

scattering, incandescence at different bands (high and narrowband), and gain mode (high and

268

low gain) (refer F-T2 of Supplementary information). In this study, we differentiate four

269

different types of arrangement of scattering and incandescence signal (i.e., amplitude vs time)

270

for size selective particles obtained from SP2, which help us to quantify the mixing state of

271

rBC (Fig. 5). Here refractory component coated with nonrefractory is referred as internal

272

mixing ( Schwarz et al., 2006 and Huang et al., 2012). If the refractory BC is not coated with

273

nonrefractory component then it is referred to as externally mixed (Huang et al., 2012). The

274

four different types are (a) mostly scattering signal dominant, (b) incandescence signal

AC C

EP

TE D

M AN U

263

11

ACCEPTED MANUSCRIPT

superimpose the scattering signal i.e. externally mixed, (c) scattering signal obtained ahead of

276

incandescence signal i.e., internally mixed, and (d) no distinct arrangement of incandescence

277

and scattering signal observed, and is therefore removed. It should be noted that the particles

278

throughout the year may have these four types of mixing states because the sources are nearly

279

constant and are of mixed type i.e., biogenic, residential, vehicular emissions, etc, at the site.

280

To better quantify the rBC mixing state in aerosol at subsaturated condition (90% RH), we

281

analyzed particles’ signal information of SP2 (Table 1). In our observations particles of size

282

below and equal to 100 nm (mostly Aitken mode) are dominated by BC (refractory and

283

absorbing) type particles (37-77%) whereas higher size particles (200 and 300 nm) are

284

dominated by mostly scattering (nonrefractory) type (63-71%) (i.e. less incandescence

285

signal). We observed that particles below 100 nm are mostly refractory BC type coming from

286

the local sources (e.g., bus, car, motor bike and auto rickshaw, etc). These are mostly primary

287

and hydrophobic in nature. Apart from this, we observed coated type BC whose number is

288

higher below and equal to 100 nm particles. This shows the transformation (uncoated to

289

coated) of BC particle due to coagulation and condensation process during transport from the

290

source to receptor site. Particles of size above 100 nm are mostly nonrefractory in nature and

291

aged aerosol which originated from both primary and secondary sources.

M AN U

SC

RI PT

275

The measured type (a), (b) and (c) account for 44, 38 and 10% within the size range

293

70 to 300 nm. Our measurement reveals that most of the aerosols are nonrefractory (44%) in

294

nature. BC obtained at this site is either externally mixed or freshly emitted soot particles

295

(38%) converse to the BC measured in other urban polluted cities and mountain sites of China

296

which were about 49% internally mixed or coated type during winter (Wang et al., 2014;

297

Zhang et al., 2017).

298

EP

3.3. Influence of rBC on HGF

AC C

299

TE D

292

12

ACCEPTED MANUSCRIPT

The HGF and BC measurement at the site is done during daytime because

301

photochemistry and microphysical properties precede the particle aging process rapidly

302

(Rieme et al., 2010). The HGF increases with increasing RH. However, presence of BC

303

suppresses the HGF effectively as illustrated in Fig. 6. The abrupt changes in HGF at 40 and

304

65% RH are better seen in Figs. 6(a) and 6(b), and HGF shows opposite behavior to BC

305

concentrations. Figure 6(c) illustrates the enhanced HGF at 90% RH (near to supersaturation),

306

which shows different relation to rBC mass concentrations especially in higher size particles

307

(>200 nm). This is because of the mixing state of BC i.e., particles of higher size are found to

308

have both nonrefractory species and BC in externally mixed state than the lower size. Most

309

BC particles are hydrophobic upon emission and get internally or externally mixed upon

310

mixing with nonrefractory species through coagulation and condensation process (Moteki et

311

al., 2004; Moffet et al., 2009). Our observation reveals that presence of BC and its mixing

312

state has significant impact on HGF and hence regulates the particle to be CCN active.

313

Aerosol characteristics depend on the time of measurement. Here aerosol characteristics refer

314

to the amount of aerosols i.e., number and mass concentrations of the particles. This will

315

result in diurnal variability of rBC concentrations. The BC mass concentration during winter

316

starts to increase about an hour before sunrise, peaks in an hour’s time and starts decreasing

317

from 08:30 hours. Further, the BC mass concentrations increase just after sunset, reach a peak

318

at around 20:00 hours and then decrease (Ramachandran and Rajesh, 2007). It should be

319

noted that BC exhibits a similar diurnal pattern throughout the year over the measurement

320

location (Rajesh and Ramachandran, 2018). However, the absolute magnitude of BC mass

321

concentrations is high during winter than in summer. Whereas the variability of HGF is

322

attributed to mixing state of rBC in an aerosol composite. Our observation shows that

323

particles at lower size contain mostly refractory and undergo core shell mixing, whereas

324

higher size is dominated by nonrefractory and undergo less core shell mixing. The

AC C

EP

TE D

M AN U

SC

RI PT

300

13

ACCEPTED MANUSCRIPT

325

observations are similar in all the sampling dates and significant changes are observed in rBC

326

mixing with respect to size rather than the time of measurement. Therefore, the time of

327

measurement will affect more the behavior of rBC rather than HGF.

328

3.4. Hygroscopicity

330

We calculated the hygroscopicity parameter from particle HGF at 90% RH. We did not

331

observe significant changes in HGF at 40% and 65% RH as shown in Figures 6(a) and 6(b).

332

However, we got significant changes in HGF at 90% RH. Therefore, aerosol hygroscopicity

333

observed at 90% RH is discussed in detail. Moreover, hygroscopic growth of aerosols will

334

become much faster near 90% RH (Engelhart et al., 2011). Water uptake by aerosol near to

335

90% RH exert an influence on aerosol optical properties, changes the planetary albedo,

336

aerosol optical depth (AOD), etc. Further, aerosol near to 90% RH plays an important role in

337

tropospheric chemistry (Gelencsér and Varga, 2005). κ is calculated at water activity,

338

typically aw~0.9 and computed for σs/a (0.072Jm−2) and T (298.15K). The average κ value

339

calculated for the period February 13 to 17 is 0.36±0.07. The measured κ value (current

340

study) is comparatively higher than that observed over northern and southern Bay of Bengal

341

(BOB) (Boreddy et al., 2016). The κ (0.27±0.15) at 90% RH obtained for 100 nm particle

342

over northern BOB constitute high hygroscopic salts such as (NH4)2SO4 associated air mass

343

from the Indo-Gangetic plains and κ (0.14±0.12) value obtained over southern

344

influenced with sea air mass constitute less hygroscopic salts such as K2SO4, MgSO4 and

345

organics associated biomass burning and sea air mass. It should be noted that the κ value over

346

northern and southern BOB have been calculated from HGF values reported by Boreddy et al.

347

(2016). The calculated κ is observed to be less compared to hygroscopicity (0.52±0.04) at

348

marine coast measured in 2003 during winter at Chichijima Island, Japan (Boreddy and

349

Kawamura, 2016). We report (the present study) hygroscopicity from an urban site where the

BOB

AC C

EP

TE D

M AN U

SC

RI PT

329

14

ACCEPTED MANUSCRIPT

atmosphere is mostly influenced with hydrophobic BC aerosol compared to marine

351

environment that has high hydrophilic species content. Therefore, the value of κ is lower

352

compared to hygroscopicity of marine aerosol. κ value is lower (0.26±0.08) for Aitken range

353

particles and higher (0.39±0.03) for accumulation range particles. κ is also a representative

354

for chemical species that constitute the aerosol particles (Petters and Kreidenweis, 2007). The

355

calculated size resolved hygroscopicity with respect to various atmospheric relevant chemical

356

species is plotted in Fig. 7. In our observations, particles in Aitken mode are dominated by

357

particles that have relatively low hygroscopicity and consisted of possibly freshly emitted BC

358

and organic compounds. Conversely, the accumulation mode range is dominated by particles

359

that have relatively high hygroscopicity and consisted of oxidized organic compounds and

360

inorganic salts. Measured ‘κ’ value predicted Aitken mode particles possibly composed of

361

glutamic acid, glutaric acid and levoglucosan. Levoglucosan is a tracer for biomass buring

362

aerosol, and glutamic and glutaric acids are the levoglucosan-OH oxidation product, therefore

363

we believe this component possibly originated from the biomass burning sources (Petters and

364

Kreidenweis, 2007; Slade et al., 2015). Likewise, ‘κ’ value predicted accumulation range

365

particles have ammonium sulfate, ammonium bisulfate and malonic acid in their composition.

366

There are no direct sources of ammonium sulfate and bisulfate at the sampling site and these

367

mainly form in the atmosphere through secondary process (Sarangi et al., 2018). Similarly,

368

malonic acid is mainly formed through SOA formation via photochemical reactions in

369

aqueous phase (Kawamura and Bikkina, 2016). It should be noted that the predicted

370

compounds are based on the calculated hygroscopicity parameter (κ) value from HGF at 90%

371

RH. κ value represent different chemical signature obtained from both laboratory and ambient

372

aerosol measurements discussed elsewhere (Petters and Kreidenweis, 2007). As explained

373

earlier, only real-time measurement by aspirating atmospheric aerosol and flow into HTDMA

374

connected to SP2 were performed in the current study. No offline sampling was made during

AC C

EP

TE D

M AN U

SC

RI PT

350

15

ACCEPTED MANUSCRIPT

375

the measurement period and hence, the study is limited to chemical analysis of particulate

376

samples.

377 378

4. Conclusions

379

In this study, black carbon mixing state and hygroscopic properties of size selective

381

urban aerosols are quantified at different relative humidity condition to better constrain the

382

aerosol indirect effect. We measured the hygroscopic growth factor and calculated the

383

hygroscopicity of size selective aerosol particles using humidified tandem differential

384

mobility analyzer (HTDMA). Further, size selective refractory black carbon mass

385

concentrations and their mixing state is determined quantitatively using single particle soot

386

photometer (SP2). For this, a measurement setup is designed by assembling HTDMA and

387

SP2 to measure size selective aerosol hygroscopic growth, rBC mass concentrations, and

388

mixing state, simultaneously. The measurement site Ahmedabad is an urban representative

389

location of mix source influence. The study is performed during winter for five consecutive

390

days from 13th to 17th February 2018. The observed mean hygroscopic growth factors (HGFs)

391

for the entire period calculated within the size range 70 to 300 nm are 1.08±2, 1.09±2, and

392

1.54±1 at 40%, 65%, and 90% RH respectively. HGF is lower (1.39±0.13) for Aitken mode

393

(≤ 100 nm) particles whereas it is higher (1.6±0.02) for accumulation mode (≥ 100 nm)

394

particles. The Aitken mode range (≤ 100 nm) is dominated by particles that have relatively

395

low hygroscopicity (0.26±0.08) and consisted of freshly emitted hydrophobic rBC and

396

organic compounds. Conversely, the accumulation mode range is dominated by particles that

397

have relatively high hygroscopicity (0.39 ±0.03) and consisted of oxidized organic

398

compounds and inorganic salts. This observation is also supported from the rBC mixing type

399

determined using SP2. SP2 data revealed that particles at lower size are mostly BC type or

400

externally mixed whereas higher size particles are mostly nonrefractory type. The mixing

AC C

EP

TE D

M AN U

SC

RI PT

380

16

ACCEPTED MANUSCRIPT

state of particles account for 44% nonrefractory and 38% externally mixed and 10%

402

internally mixed or coated type within the size range 70 to 300 nm. κ value further suggests

403

that Aitken mode particles possibly composed of glutamic acid, glutaric acid and

404

levoglucosan from biomass burning sources, whereas accumulation range particles have

405

ammonium sulfate, ammonium bisulfate and malonic acid in their composition and the

406

possible source would be secondary in origin. This study provides the first direct evidence on

407

size selective BC mixing state determined quantitatively and its influence over size selective

408

HGF from India. Our study revealed that particles at different size ranges have different

409

mixing state (i.e., lower size are mostly refractory (37-77%) and higher size are nonrefractory

410

(63-71%)) and compositions and can perturb the hygroscopic growth and hence the CCN

411

activation at different sizes. The data reported here are also useful for constraining different

412

aerosol linked air quality and climate models used for predicting CCN activities and hence

413

the aerosol indirect effect.

SC

RI PT

401

414

Acknowledgments:

M AN U

415

We are thankful to the Gujarat pollution control board (GPCB) and central pollution

417

control board for providing meteorological data. The authors gratefully acknowledge the

418

NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and

419

dispersion model (http://www.ready.noaa.gov). The synoptic surface winds for February 2018

420

are obtained from European Centre for Medium-Range Weather Forecasts (ECMWF)

421

(https://www.ecmwf.int). We thank Piyushkumar N. Patel for his help in drawing Figure 2.

422 423

EP

Supplementary data

AC C

424

TE D

416

17

ACCEPTED MANUSCRIPT

425

Description of size selective humidified particle number concentrations and

426

hygroscopic growth factor in a table (SI-T1). Figures presenting the schematic of HTDMA

427

(SI-F1) and Signal information of SP2 illustrating different mixing states of aerosol typically

428

observed in Ahmedabad (SI-T2) during the study period.

429 430

References

431

Aggarwal, S.G., Mochida, M., Kitamori, Y., and Kawamura, K., 2007 Chemical Closure

433

Study on Hygroscopic Properties of Urban Aerosol Particles in Sapporo, Japan,

434

Environ. Sci. Technol., 41, 6920–6925.

Baumgardner, D., Kok, G., Raga, G., 2004. Warming of the Arctic lower stratosphere by light

436

absorbing

particles.

Geophys.

437

dx.doi.org/10.1029/2003GL018883.

Res.

Lett.

31(6),

1–4,

http://

SC

435

RI PT

432

Baumgardner, D., Popovicheva, O., Allan, J., Bernardoni, V., Cao, J., Cavalli, F., Cozic, J.,

439

Diapouli, E., Eleftheriadis, K., Genberg, P.J., Gonzalez, C., Gysel, M., John, A.,

440

Kirchstetter, T.W., Kuhlbusch, T.A.J., Laborde, M., Lack, D., Müller, T., Niessner, R.,

441

Petzold, A., Piazzalunga, A., Putaud, J.P., Schwarz, J., Sheridan, P., Subramanian, R.,

442

Swietlicki, E., Valli, G., Vecchi, R., Viana, M., 2012. Soot reference materials for

443

instrument

444

recommendations. Atmos. Meas. Tech. 5, 1869-1887, http:// dx.doi.org/10.5194/amt-5-

445

1869-2012.

and

intercomparisons:

TE D

calibration

M AN U

438

a

workshop

summary

with

446

Boreddy, S.K.R., Kawamura, K., 2016. Hygroscopic growth of water-soluble matter extracted

447

from remote marine aerosols over the western North Pacific: Influence of pollutants

448

transported

449

dx.doi.org/10.1016/j.scitotenv.2016.03.096.

East

Asia.

Sci.

AC C

EP

from

Total.

18

Environ.,

557,

285–295;

http://

ACCEPTED MANUSCRIPT

450

Boreddy, S.K.R., Kawamura, K., Bikkina, S., and Sarin, M.M., 2016. Hygroscopic growth of

451

particles nebulized from water-soluble extracts of PM2.5 aerosols over the Bay of

452

Bengal: Influence of heterogeneity in air masses and formation pathways, Sci. Total

453

Environ., 544, 661–669.

454

Charlson, R.J., Schwartz, S.E., Hales, J.M., Cess, R.D., Coakley, J.A., Hansen, J.E.,

455

Hofmann, D.J., 1992. Climate forcing by anthropogenic aerosols. Science. 255, 423–

456

430. http:// dx.doi.org/10.1126/science.255.5043.423.

458

Chung, S.H., Seinfeld, J.H., 2002. Global distribution and climate forcing of carbonaceous

RI PT

457

aerosols. J Geophys Res. 107(D19), D4407. http:// dx.doi.org/10.1029/2001JD001397.

Deshpande, R. D., Maurya, A. S., Kumar, B., Sarkar, A., and Gupta, S. K., 2010 Rain-vapor

460

interaction and vapor source identification using stable isotopes from semiarid western

461

India. J. Geophys. Res., 115, D23311, doi:10.1029/2010JD014458.

SC

459

Engelhart, G. J., Hildebrandt, L., Kostenidou, E., Mihalopoulos, N., Donahue, N. M., and

463

Pandis, S. N., 2011 Water content of aged aerosol. Atmos. Chem. Phys., 11, 911–920,

464

doi:10.5194/acp-11- 911-2011.

M AN U

462

465

Gelencsér and Varga, 2005. Evaluation of the atmospheric significance of multiphase

466

reactions in atmospheric secondary organic aerosol formation. Atmos. Chem. Phys., 5,

467

2823–2831, doi:10.5194/acp5-2823-2005.

468

Ghan, S.J., Zaveri, R.A., 2007. Parameterization of optical properties for hydrated internallymixed

aerosol.

J.

Geophys.

470

dx.doi.org/10.1029/2006JD007927.

Res.

TE D

469

112,

D10201,

http://

Guo, S., Hu, M., Lin, Y., Gomez-Hernandez, M., Zamora, M.L., Peng, J.F., Collins, D.R.,

472

Zhang, R.Y., 2016. OH-Initiated Oxidation of m-Xylene on Black Carbon Aging.

473

Environ. Sci. Technol. 50, 8605–8612. http:// dx.doi.org/10.1021/acs.est.6b01272.

AC C

EP

471

19

ACCEPTED MANUSCRIPT

474

Gysel, M., Crosier, J., Topping, D.O., Whitehead, J.D., Bower, K.N., Cubison, M.J.,

475

Williams, P., Flynn, M., McFiggans, G., Coe, H., 2007. Closure between chemical

476

composition and hygroscopic growth of aerosol particles during TORCH2, in

477

Nucleation and Atmospheric Aerosols, edited by C. O’Dowd and P. Wagner., pp. 731–

478

735, Springer, Netherlands. http:// dx.doi.org/10.1007/978-1-4020-6475-3_144. Hersey, S.P., Craven, J.S., Metcalf, A.R., Lin, J., Lathem, T., Suski, K.J., Cahill, J.F., Duong,

480

H.T., Sorooshian, A., Jonsson, H.H., Hersey, S.P., Craven, J.S., Metcalf, A.R., Lin, J.,

481

Lathem, T., Suski, K.J., Cahill, J.F., Duong, H.T., Sorooshian, A., Jonsson, H. H.,

482

Shiraiwa, M., Zuend, A., Nenes, A., Prather, K.A., Flagan, R. C., Seinfeld, J.H., 2013,

483

Composition and hygroscopicity of the Los Angeles Aerosol: CalNex. J. Geophys.

484

Res.-Atmos. 118, 3016–3036, http:// dx.doi.org/10.1002/jgrd.50307.

RI PT

479

Hersey, S.P., Sorooshian, A., Murphy, S.M., Flagan, R.C., Seinfeld, J.H., 2009. Aerosol

486

hygroscopicity in the marine atmosphere: a closure study using high-time-resolution,

487

multiple-RH DASHSP and size-resolved C-ToF-AMS data. Atmos. Chem. Phys. 9,

488

2543–2554, http:// dx.doi.org/10.5194/acp-9-2543-2009.

M AN U

SC

485

489

Huang, X. F., Sun, T. L., Zeng, L. W., Yu, G. H., and Luan, S. J., 2012 Black carbon aerosol

490

characterization in a coastal city in South China using a single particle soot photometer.

491

Atmos. Environ., 51, 21–28, doi:10.1016/j.atmosenv.2012.01.056.

Jacobson, M.Z. 2001. Strong radiative heating due to the mixing state of black carbon in

493

atmospheric aerosols. Nature. 409, 695–697. http:// dx.doi.org/10.1038/35055518.

494

Jimenez, J.L., Canagaratna, M. R., Donahue, N.M., Prevot, A.S.H., Zhang, Q., Kroll, J.H.,

495

DeCarlo, P. F., Allan, J.D., Coe, H., Ng, N.L., 2009. Evolution of organic aerosols in

496

the atmosphere. Science. 326, 1525−1529, http:// dx.doi.org/10.1126/science.1180353.

AC C

EP

TE D

492

20

ACCEPTED MANUSCRIPT

497

Kawamura, K., Bikkina, S. 2016. A review of dicarboxylic acids and related compounds in

498

atmospheric aerosols: Molecular distributions, sources and transformation. Atmos. Res.,

499

170, 140–160, https://doi.org/10.1016/j.atmosres.2015.11.018.

500

Kiss, G., Tombacz, E., Hansson, H.C., 2005. Surface tension effects of humic like substances

501

in the aqueous extract of tropospheric fine aerosol. J. Atmos. Chem., 50, 279–294.

502

http:// dx.doi.org/10.1007/s10874-005-5079-5. Koch, D., 2001. Transport and direct radiative forcing of carbonaceous and sulfate aerosols in

504

the GISS GCM. J. Geophys. Res. 106(D17), 20311–20332; 1971. http://

505

dx.doi.org/10.1029/2001JD900038.

506 507

RI PT

503

Köhler, H., 1936.The nucleus in and the growth of hygroscopic droplets. Trans Farad Soc. 32, 1152–1161. http:// dx.doi.org/10.1039/TF9363201152.

Laaksonen, A., Hamde, A., Joutsensaari, J., Hiltunen, L., Cavalli, F., Junkermann, W., Asmi,

509

A., Fuzzi, S., Faccini, M.C., 2005. Cloud condensation nucleus production from

510

nucleation events at a highly polluted region. Geophys. Res. Lett. 32, L06812. http://

511

dx.doi.org/10.1029/2004GL022092.

M AN U

SC

508

512

Laskina, O., Morris, H.S., Grandquist, J.R., Qin, Z., Stone, E.A., Tivanski, A.V., Grassian,

513

V.H., 2015. Size matters in the water uptake and hygroscopic growth of

514

atmospherically relevant multicomponent aerosol particles. J. Phys. Chem. A. 119,

515

4489–4497, http:// dx.doi.org/10.1021/jp510268p.

Levin, E.J.T., Prenni, A.J., Palm, B.B., Day, D.A., Campuzano-Jost, P., Winkler, P. M.,

517

Kreidenweis, S.M., DeMott, P.J., Jimenez, J.L., Smith, J.N., 2014. Size-resolved

518

aerosol composition and its link to hygroscopicity at a forested site in Colorado. Atmos.

519

Chem. Phys. 14, 2657-2667, http:// dx.doi.org/10.5194/acp-14-2657-2014.

AC C

EP

TE D

516

21

ACCEPTED MANUSCRIPT

520

Liu, X. H., Penner, J. E., Herzog, M., 2005. Global modeling of aerosol dynamics: Model

521

description, evaluation, and interactions between sulfate and nonsulfate aerosols. J.

522

Geophys. Res. 110(D18), D18206. http:// dx.doi.org/10.1029/2004JD005674.

523

Lohmann, U., Hoose, C., 2009. Sensitivity studies of different aerosol indirect effects in

524

mixed-phase clouds. Atmos. Chem. Phys. 9, 8917–8934, http:// dx.doi.org/10.5194/acp-

525

9-8917-2009. Moffet, R.C., Prather, K.A., 2009. In-situ measurements of the mixing state and optical

527

properties of soot with implications for radiative forcing estimates. P. Natl. Acad. Sci.

528

USA. 106, 11872–11877. http:// dx.doi.org/10.1073/pnas.0900040106.

RI PT

526

Moteki, N., Kondo, Y., Miyazaki, Y., Takegawa, N., Komazaki, Y., Kurata, G., Shirai, T.,

530

Blake, D.R., Miyakawa, T., Koike, M., 2004. Evolution of mixing state of black carbon

531

particles: aircraft measurements over the western Pacific in March. Geophys. Res. Lett.

532

34, L11803. http:// dx.doi.org/10.1029/2006GL028943.

SC

529

Murphy, D.M., Thomson, D.S., Mahoney, T.M.J., 1998. In situ measurements of organics,

534

meteoritic material, mercury, and other elements in aerosols at 5 to 19km. Science.

535

282(5394), 1664–1669. http:// dx.doi.org/10.1126/science.282.5394.1664.

M AN U

533

536

Peng, J.F., Hu, M., Guo, S., Du, Z.F., Shang, D.J., Zheng, J., Zeng, L.M., Shao, M., Wu, Y.S.,

537

Collins, D.; Zhang, R.Y., 2017. Ageing and hygroscopicity variation of black carbon

538

particles in Beijing measured by a quasi-atmospheric aerosol evolution study

539

(QUALITY)

540

dx.doi.org/10.5194/acp-17-10333-2017.

Atmos.

Chem.

Phys.

TE D

chamber.

17,

10333-10348.

http://

Petters, M.D., Kreidenweis, S.M.A., 2007. Single parameter representation of hygroscopic

542

growth and cloud condensation nucleus activity. Atmos. Chem. Phys. 7, 1961–1971.

543

http:// dx.doi.org/10.5194/acp-7-1961-2007.

AC C

EP

541

22

ACCEPTED MANUSCRIPT

544

Rajesh, T.A., Ramachandran, S., 2017. Characteristics and source apportionment of black

545

carbon aerosols over an urban site. Environ. Sci. Pollut. Res. 24(9), 8411-8424; http://

546

dx.doi.org/10.1007/s11356-017-8453-3.

547

Rajesh, T.A., Ramachandran, S., 2018. Black carbon aerosols over urban and high altitude

548

remote regions: Characteristics and radiative implications. Atmospheric Environment,

549

194, 110-122, https://doi.org/10.1016/j.atmosenv.2018.09.023. Ramachandran, S., Rajesh, T.A., 2007. Black carbon aerosol mass concentration over

551

Ahmedabad, an urban location in western India: Comparison with urban sites in Asia,

552

Europe, Canada, and the United States. J. Geophys. Res. 112, D06211, http://

553

dx.doi.org/10.1029/2006JD007488.

RI PT

550

Ramachandran, S., Srivastava, R., Kedia, S., Rajesh, T.A., 2012. Contribution of natural and

555

anthropogenic aerosols to optical properties and radiative effects over an urban location.

556

Environ. Res. Lett. 7, D034028. http:// dx.doi.org/10.1088/1748-9326/7/3/034028.

557

Sarangi, B., Aggarwal, S.G., Kunwar B., Kumar, S., Kaur, R., Sinha, D., Tiwari, S.,

558

Kawamura, K., 2012. Nighttime particle growth observed during spring in New Delhi:

559

Evidence for the aqueous phase oxidation of SO2, Atmospheric Environment, 188, 82-

560

96, https://doi.org/10.1016/j.atmosenv.2018.06.018.

M AN U

SC

554

561

Sarangi, B., Aggarwal S.G., Gupta, P.K., 2017. Performance check of particle size standards

562

within and after shelf life using differential mobility analyzer. J. Aerosol Sci. 103, 24-

563

27. http:// dx.doi.org/10.1016/j.jaerosci.2016.10.002.

Schwarz, J., Gao, R., Fahey, D., Thomson, D., Watts, L., Wilson, J., Reeves, J., Darbeheshti,

565

M., Baumgardner, D., Kok, G., Chung, S. H., Schulz, M., Hendricks, J., Lauer, A.,

566

Kärcher, B., Slowik, J.G., Rosenlof, K.H., Thompson, T.L., Langford, A.O.,

567

Loewenstein, M.; and Aikin, K.C., 2006. Single-particle measurements of midlatitude

568

black carbon and light-scattering aerosols from the boundary layer to the lower

AC C

EP

TE D

564

23

J.

ACCEPTED MANUSCRIPT Res. Atmos. 111, D16207.

569

stratosphere.

Geophys.

570

dx.doi.org/10.1029/2006JD007076.

http://

571

Sheridan, P., Jefferson, A., Ogren, J., 2002. Spatial variability of submicrometer aerosol

572

radiative properties over the Indian Ocean during INDOEX. J. Geophys. Res.

573

107(D19), 8011, http:// dx.doi.org/10.1029/2000JD000166. Shimada, M., Lee, H.M., Kim, C.S., Koyama, H., Myojo, T., Okuyama, K., 2005.

575

Development of an LDMA-FCE system for the measurement of submicron aerosol

576

particles. J. Chem. Eng. Jpn. 38, 34–44, http:// dx.doi.org/10.1252/jcej.38.34.

RI PT

574

Slade, J.H., Thalman, R., Wang, J., and Knopf, D.A., 2015. Chemical aging of single and

578

multicomponent biomass burning aerosol surrogate particles by OH: implications for

579

cloud condensation nucleus activity. Atmos. Chem. Phys., 15, 10183-10201,

580

https://doi.org/10.5194/acp-15-10183-2015.

SC

577

Stephens, M., Turner, N., Sandberg, J., 2003. Particle identification by laser-induced

582

incandescencence in a solid-state laser cavity. Appl. Opt. 42, 3726–3736. http://

583

dx.doi.org/10.1364/ao.42.003726.

M AN U

581

584

Wang, Q., Huang, R.-J., Cao, J., Han, Y., Wang, G., Li, G., Wang, Y., Dai, W., Zhang, R.,

585

Zhou, Y., 2014. Mixing State of Black Carbon Aerosol in a Heavily Polluted Urban

586

Area of China: Implications for Light Absorption Enhancement. Aerosol Sci. Technol.

587

48, 689–697. http:// dx.doi.org/10.1080/02786826.2014.917758.

588

Wang, Y., Khalizov, A., Levy, M., Zhang, R., 2013. Light absorbing aerosols and their atmospheric

impacts.

Atmos.

Environ.

590

dx.doi.org/10.1016/j.atmosenv.2013.09.034.

TE D

589

81,

713–715.

http://

Wang, Y., Wan, Q., Meng, W., Liao, F., Tan, H., Zhang, R., 2011. Long-term impacts of

592

aerosols on precipitation and lightning over the Pearl River Delta megacity area in

AC C

EP

591

24

ACCEPTED MANUSCRIPT

593

China. Atmos. Chem. Phys. 11, 12421–12436. http:// dx.doi.org/10.5194/acp-11-12421-

594

2011.

595

Willis, M.D., Healy, R.M., Riemer, N., West, M., Wang, J.M., Jeong, C.-H., Wenger, J.C.,

596

Evans, G.J., Abbatt, J.P.D., and Lee, A.K.Y., 2016 Quantification of black carbon

597

mixing state from traffic: implications for aerosol optical properties, Atmos. Chem.

598

Phys., 16, 4693-4706, https://doi.org/10.5194/acp-16-4693-2016. Wu, Z.J., Poulain, L., Henning, S., Dieckmann, K., Birmili, W., Merkel, M., van Pinxteren,

600

D., Spindler, G., Müller, K., Stratmann, F., Herrmann, H., Wiedensohler, A., 2013.

601

Relating particle hygroscopicity and CCN activity to chemical composition during the

602

HCCT-2010 field campaign. Atmos. Chem. Phys. 13, 7983– 7996, http://

603

dx.doi.org/10.5194/acp-13-7983-2013.

RI PT

599

Yuan, T., Li, Z., Zhang, R., Fan, J., 2008. Increase of cloud droplet size with aerosol optical

605

depth: An observation and modeling study. J. Geophys. Res. 113, D04201. http://

606

dx.doi.org/10.1029/2007JD008632.

SC

604

Zelenyuk, A., Imre, D., Earle, M., Easter, R., Korolev, A., Leaitch, R., Liu, P., Macdonald,

608

A.M., Ovchinnikov, M., Strapp, W., 2010. In situ characterization of cloud

609

condensation nuclei, interstitial, and background particles using the single particle mass

610

spectrometer,

611

dx.doi.org/10.1021/ac1013892.

SPLAT

II†.

Anal.

M AN U

607

Chem.

82,

7943–7951.

http://

Zhang, G., Lin, Q., Peng, L., Bi, X., Chen, D., Li, M., Li, L., Brechtel, F.J., Chen, J., Yan,

613

W., Wang, X., Peng, P., Sheng, G., Zhou, Z., 2017. The single-particle mixing state and

614

cloud scavenging of black carbon: a case study at a high-altitude mountain site in

615

southern China. Atmos. Chem. Phys. 17, 14975-14985, http:// dx.doi.org/10.5194/acp-

616

17-14975-2017, 2017.

AC C

EP

TE D

612

25

ACCEPTED MANUSCRIPT

Zhang, Q., Jimenez, J. L., Canagaratna, M. R., Allan, J. D., Coe, H., Ulbrich, I., Alfarra, M.

618

R., Takami, A., Middlebrook, A. M., Sun, Y. L., Dzepina, K., Dunlea, E., Docherty, K.,

619

DeCarlo, P. F., Salcedo, D., Onasch, T., Jayne, J. T., Miyoshi, T., Shimono, A.,

620

Hatakeyama, S., Takegawa, N., Kondo, Y., Schneider, J., Drewnick, F., Borrmann, S.,

621

Weimer, S., Demerjian, K., Williams, P., Bower, K., Bahreini, R., Cottrell, L., Griffin,

622

R.J., Rautiainen, J., Sun, J.Y., Zhang, Y.M., Worsnop, D.R., 2007. Ubiquity and

623

dominance of oxygenated species in organic aerosols in anthropogenically-influenced

624

Northern Hemisphere midlatitudes. Geophys. Res. Lett. 34, L13801. http://

625

dx.doi.org/10.1029/2007GL029979.

RI PT

617

626 627 628

SC

629 630 631

M AN U

632 633 634 635 636 637 638 639

643 644 645 646 647

EP

642

AC C

641

TE D

640

26

ACCEPTED MANUSCRIPT

648 649 650 651

Table

652 653 654

Table 1. DMA sized particle counts measured using SP2 and quantifying different rBC mixing types in aerosol obtained during the study period. Mixing Type

a

DMA particle size (nm) 70 100 200 300 Mean (%) over the period (February 13-17) 4 41 71 63

b

77

37

918 8724 13019 4588

c

8

13

895 2944 9907

d

11

9

Date 70

200

300

SP2 particle counts 128 1671 7502 2615 136 1391 4361

1616

294 1783 5527

2599

3613

657 658 659 660 661 662

667 668 669 670

EP

666

AC C

665

TE D

663 664

12

24

10

10

7

3

M AN U

February 13th February 14th February 15th February 16th February 17th

100

RI PT

DMA particle size (nm)

SC

655 656

27

ACCEPTED MANUSCRIPT

671 672 673

Figure Legends

674 675

Fig. 1. Left panel illustrates sampling site and the right panel describe the experimental setup.

676

-1 Fig. 2(a). Surface level synoptic wind pattern (ms ) during the study period. (b) Five day

677

mean air back trajectory corresponding to 500 m over Ahmedabad. The color scale represents

678

the altitude (m) from where the air mass reaches the measurement location.

679

Fig. 3. Left plot shows the humidified particle size distributions for 100 nm particles at 40, 65

681

and 90% RH, and the plots on right side show the mode type (uni-modal at lower size i.e.,

682

100 nm and bi-modal at higher size i.e., 300 nm) size distributions of aerosol particles at

683

90% RH.

RI PT

680

684

Fig. 4. (a) rBC mass concentration distributions within particle size range 70-300 nm, (b) rBC

686

mass concentrations measured on consecutive dates during February 13 - 17, 2018. Vertical

687

bars indicate ±1σ deviation from the mean.

SC

685

688

Fig. 5. Scattering and incandescence signals representing the different mixing types of rBC as obtained from the SP2 measurement made in Ahmedabad.

692 693 694

Fig. 6. Size selective hygroscopic growth factor (HGF) at (a) 40%, (b) 65%, and (c) 90% RH with corresponding size selective rBC mass concentrations measured during February, 2018.

695 696

Fig. 7. Size resolved hygroscopicity and the corresponding predicted atmospheric relevant chemical species

M AN U

689 690 691

697

701 702 703 704 705

EP

700

AC C

699

TE D

698

28

ACCEPTED MANUSCRIPT

706 707 708

Figure 1.

709

RI PT

710

SC

711 712 713 714 715

M AN U

716 717 718

EP AC C

720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735

TE D

719

29

736 737 738

ACCEPTED MANUSCRIPT Figure 2.

739

EP AC C

742 743 744

TE D

M AN U

SC

RI PT

740 741

30

ACCEPTED MANUSCRIPT

745 746 747

Figure 3.

SC

RI PT

748 749 750

M AN U

751 752 753 754 755 756 757 758 759

763 764 765 766

EP

762

AC C

761

TE D

760

31

ACCEPTED MANUSCRIPT

767 768 769

Figure 4.

M AN U

SC

RI PT

770

EP AC C

772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788

TE D

771

32

789 790 791

ACCEPTED MANUSCRIPT Figure 5.

M AN U

SC

RI PT

792

793 794 795 796 797 798

802 803 804 805 806

EP

801

AC C

800

TE D

799

33

ACCEPTED MANUSCRIPT

807 808 809

Figure 6.

RI PT

810

M AN U TE D EP AC C

812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837

SC

811

34

ACCEPTED MANUSCRIPT Figure 7.

SC

RI PT

838 839 840

M AN U

841

AC C

EP

TE D

842 843

35

ACCEPTED MANUSCRIPT Highlights Size selective rBC mixing state quantified down to 70 nm.

•

rBC mixing characteristics are different for different size particles.

•

rBC mixing state has strong implication over aerosol hygroscopic growth.

•

Hygroscopicity is determined to predict size resolved aerosol chemical compositions.

AC C

EP

TE D

M AN U

SC

RI PT

•