1
Source Apportionment Using Radiocarbon and Organic
Tracers for PM
2.5
Carbonaceous Aerosols in Guangzhou, South
China: Contrasting Local- and Regional-Scale Haze Events
Junwen Liu
1,4
, Jun Li
1*
, Yanlin Zhang
2
, Di Liu
1
, Ping Ding
3
, Chengde Shen
3
,
Kaijun Shen
1,4
, Quanfu He
1,4
, Xiang Ding
1
, Xinming Wang
1
, Duohong Chen
1
,
Sönke Szidat
2
, Gan Zhang
1
1
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of
Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
2
Department of Chemistry and Biochemistry & Oeschger Centre for Climate
Change Research, University of Bern, Berne, 3012, Switzerland
3
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of
Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
4
University of Chinese Academy of Sciences, Beijing, 100049, China
*
Corresponding author
Acceptedversion
Publishedin
EnvironmentalScienceandTechnology48(2014)12002‐12011
http://dx.doi.org/10.1021/es503102w
2
Abstract 1
We conducted a source apportionment and investigated the atmospheric 2
behavior of carbonaceous aerosols during hazy and normal days using 3
radiocarbon (
14
C) and biomass burning/secondary organic aerosol (SOA) 4
tracers during winter in Guangzhou, China. Haze episodes were formed either 5
abruptly by local emissions or through the accumulation of particles transported 6
from other areas. The average contributions of fossil carbon to elemental 7
carbon (EC), water-insoluble organic carbon, and water-soluble organic carbon 8
were 71 ± 10%, 40 ± 6% and 33 ± 3%, respectively. High contributions of fossil 9
carbon to EC (80−90%) were observed for haze samples that were 10
substantially impacted by local emissions, as were the highest (lowest) ratios 11
for NO
3
−
/SO
4
2−
(OC/EC), which indicates that these particles mainly came from 12
local vehicle exhaust. Low contributions of fossil carbon to EC (60−70%) were 13
found for haze particles impacted by regional transport. Secondary organic 14
carbon (SOC) calculated using SOA tracers accounts for only ∼20% of the SOC 15
estimated by
14
C, which is probably because some important volatile organic 16
carbons are not taken into account in the SOA tracer calculation method and 17
because of the large discrepancy in ambient conditions between the 18
atmosphere and smog chambers. A total of 33 ± 11% of the SOC was of fossil 19
origin, a portion of which could be influenced by humidity. 20
Keywords: Haze,
14
C, organic tracer, secondary organic carbon, PM
2.5
21
3
22
TOC 23
4
1 Introduction
Haze episodes in China occur frequently, causing extensive public and
scientific concern.
1,2
Haze particles exert a severe influence on not only human
health and air quality,
2
but also the climatic system.
3
The main cause of this
haze is the rapid or persistent enhancement of fine particle (PM
2.5
, i.e., particles
with an aerodynamic diameter less than 2.5 μm) concentrations in the air,
accompanied by relatively stable synoptic conditions. These PM
2.5
particles can
either be emitted from local sources or transported from other regions through
atmospheric movement.
Carbonaceous aerosols account for a large fraction of PM
2.5
particles
(∼20−90%)
4
and are considered to be a vital constituent controlling the
formation and evolution of haze episodes. Extremely high concentrations of
carbonaceous aerosols (∼100 μg C/m
3
) have been recorded during typical
haze days in northern China,
5
as well as in southern
6
and central China.
7
Generally, carbonaceous aerosols can be categorized into organic carbon (OC)
and elemental carbon (EC) based on their thermal, chemical, and optical
properties. EC is emitted directly from incomplete combustion (e.g., wood fire,
traffic, and industry emissions) and is frequently used as a primary tracer due
to its inert physiochemical properties in the atmosphere. OC includes primary
sources of emission (e.g., biogenic sources, biomass burning, traffic, cooking,
industry, soil, etc.) and secondary organic carbon (SOC), which is formed by
the atmospheric oxidation of gaseous precursors.
4,8
Water-soluble organic
5
carbon (WSOC) mainly comprises compounds with polar functional groups,
such as polyols, and (poly-)carboxylic acids;
9
these chemicals are mainly
derived from primary biomass burning and SOC.
10,11
For episodes with limited
biomass burning activity, WSOC is frequently used as an SOC tracer.
10,12
Water-insoluble organic carbon (WIOC) includes alkanes, polycyclic aromatic
hydrocarbons, plant debris, and bacteria. Although carbonaceous aerosols play
an important role in air pollution and haze formation, knowledge of their
emission sources and atmospheric behavior (including the characteristics of
biomass vs fossil fuel emissions and the differences between primary and
secondary sources) are still poorly understood.
Radiocarbon (
14
C) measurements allow unambiguous differentiation between
fossil and nonfossil sources. The underlying principle of
14
C measurements is
that this radioisotope has become extinct in fossil fuel carbon, while its
contemporary level is relatively constant.
13,14
With a combination of organic
tracers, detailed source apportionments of carbonaceous aerosols can be
achieved via
14
C analysis. These data are very helpful to understand the
evolution mechanisms of haze and SOC in the real atmosphere, with an aim of
controlling pollutant emissions. So far, such studies are still scarce and have
mainly been conducted in developed countries in Europe
15−18
or the United
States.
19,20
Only a few studies have been performed in Chinese cities
21,22
or
rural sites.
23,24
Guangzhou (23.1°N, 113.3°E) is the largest city in the subtropical zone of
