DATA ANALYSIS

The infrared fingerprint of the soluble fraction of atmospheric aerosol: towards the identification of functional

groups influencing oxidative potential

OUTLOOK

The Fourier transform infrared (FTIR) spectroscopy allows the measurement of

absorption peaks, due to vibrational transitions of chemical bonds, leading to the

identification and quantification of main functional groups in a complex system.

In this work, we have employed the ATR-FTIR technique for analyzing thin solid films

of particulate matter (PM) components, extracted from filter-deposited aerosol

material, by solubilization in deionized water. The goal was the identification of

functional groups, soluble in aqueous biological fluids, able to influence the

toxicological potential of airborne particles, in order to elucidate the relationships

between PM chemical characteristics and human health effects.

THE TECHNIQUE

In the attenuated total reflectance (ATR) mode, the sample is placed

directly on a transparent crystal with a high refractive index, through which

the IR beam is passed. The spectrum is then measured detecting the

attenuation of the light reflected within the crystal and delivered to the

detector. The path length depends solely on the penetration depth of the

evanescent wave beyond the interface; therefore, the technique is suitable

for analyzing thin solid films with high sensitivity and repeatability.

CONCLUSIONS• The ATR-FTIR technique represents a useful tool, able to identify

and quantify simultaneously different chemical groups of PM samples.

• This method offers the advantage of no requirement of complex sample treatment, making the analysis simple and fast.

• It proves to be complementary to different characterization techniques and is expected to give valuable contribution in order to highlight useful correlations between air quality and effects on

human health.

SAMPLE COLLECTION

PM2.5 and PM10 samples on quartz substrates were

collected at the Environmental-Climate

Observatory of Lecce, located at the ISAC-CNR

premises in Lecce (40°20’8’’N-18°07’28’’E, 37 m asl).

Samples were collected using a dual channel

sampler (SWAM, Fai Instruments))

The pH of the solutions, resulting from the

extraction of water-soluble particulatematter, was found strictly dependent on the

PM origin. Lower pH is associated to highOC content, whilst higher pH was found for

Saharan dust-rich samples

Acquisition of standard

compounds spectra allowed toidentify IR signatures for nitrate,

ammonium, sulfate andcarbonate/bicarbonate.

The analysis of different amounts

of sodium sulfate demonstratedthat quantitative measurements

are feasible.

ATR apparatus

horizontal sampling system

SOLUBILIZATION AND DEPOSITION PROTOCOL

Filter (0.80 cm2)

ultrasonic bath at 40 °C

centrifugationunsolubilized material

sonication for 10 min at 40°C

1 mL deionized water

Prism

Prism

Dry down

Application of 4 mL solution

onto the ATR crystal

solvent evaporation

and spectrum

acquisition

PM 10 sample pH PM 2.5 sample pH

A505 6.6 B505 6.8

A480 5.2 B480 6.0

A479 6.1 B479 5.7

A451 6.5 B451 6.1

A893 7.4 B893 7.1

A520 7.7 B520 7.1

A457 7.1 B457 7.0

STANDARD COMPOUNDS SPECTRA

Na2SO4

SPECTRA OF PM10 AND PM2.5 SOLUBLE FRACTIONS

Based on their known

properties, analyzedsamples can be grouped in

three classes:

• Blue: samples collectedduring Saharan dustevents

• Red: samples with high OC content

• Black: sample with standard characteristics

The comparison with

standard compound spectra and with literature data led to the identification

of marker bands for nitrate, sulfate and carbonyl

compounds.

PM2.5

sample

Mass

(µg/m3)

OC

(µg/m3)

DTT oxidation

rate (min-1)

Carbonyls

absorption

(A.U.)

Sulfate

absorption

(A.U.)

Nitrate

absorption

(A.U.)

B505 10.40 2.64 0.238219 0.0013 0.0154 0.135

B480 47.10 21.16 0.585956 0.0067 0.0162 0.021

B479 82.50 36.25 0.691174 0.0143 0.0305 0.0482

B451 48.30 21.21 0.486134 0.0067 0.0208 0.0267

B893 30.10 2.57 0.235401 0.0018 0.0137 0.0147

B520 28.10 1.26 0.196056 0.0018 0.0130 0.0142

B457 25.70 3.38 0.283017 0.0017 0.0097 0.0311

PM10

sample

Mass

(µg/m3)

OC

(µg/m3)

DTT oxidation

rate (min-1)

Carbonyls

absorption

(A.U.)

Sulfate

absorption

(A.U.)

Nitrate

absorption

(A.U.)

A505 19.00 3.05 0.346848131 0.0041 0.0161 0.0158

A480 51.50 21.31 0.6324967 0.0069 0.0163 0.0184

A479 89.40 36.14 0.767564263 0.0143 0.0367 0.0589

A451 59.30 24.18 0.602082197 0.0063 0.02052 0.0261

A893 130.30 6.83 0.299105827 - 0.0212 0.0253

A520 107.20 3.86 0.22857746 - 0.0192 0.0137

A457 99.70 5.34 0.330941843 0.0012 0.018 0.0119

The relative intensity of absorption

bands revealed that PM10 and PM2.5

samples present a similar content of

sulfates, in agreement with the

association of this component, of

secondary origin, manly to fine particles.

Infrared spectra of PM10 and PM2.5 samples revealed that organic compounds bearing carbonyl groups are mainly associated to fine

particles.

The intensity of carbonyl group absorption bands is directly correlated to the OC content and to the oxidative potential of the sample,

thus suggesting that the presence of C=O groups is linked to the aerosol ability to promote the generation of reactive oxygen species

(ROS).

L. Giotta1, M.R. Guascito1, 2, M. Zollino1, D. Chirizzi2, L. Valli1, D. Cesari2, A. Dinoi2, D. Contini2

1Department of Biological and Environmental Sciences and Technologies, University of Salento, Lecce, 73100, Italy2Institute of Atmospheric Sciences and Climate, ISAC-CNR, Lecce, 73100, Italy