International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
SUN Yangyang 1 , CHEN Linghong 1 , ZHU Jie 1 , ZUO Lei 1 , JIAO Li 2 , GAO Xiang 1 , CEN Kefa 1
1 State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China
2 Hangzhou Environmental Monitoring Center, Hangzhou 310007, China
ABSTRACT
The toxicity and damage to environment of secondary particles in atmospheric PM2.5 has been the focus for the public in China. Reaction mechanism of secondary PM2.5 was reviewed including atmospheric photochemical reactions of secondary organic carbon (SOA) between VOCs and oxidants such as OH, NOx, O
3
, transformation mechanism of benzene, phenol and diolefin, and heterogeneous reactions of SO
2
and NOx on mineral dust in urban areas. Three theoretical models were illustrated to determine the contribution of secondary particles from different types of emission sources. Chemical Mass Balance model (CMB) as source apportionment receptor models calculates the linear summation of each source concentration contribution to compute the secondary particles concentration of the receptor. For uncertain sources, statistical methods are adopted which can give birth to other receptors such as positive matrix factorization method (PMF). Organic tracer method is introduced in receptor models to study secondary organic particulates. In Community Multi-scale Air Quality (CMAQ) modeling system, photochemical reactions are coupled with meteorological data and gridded emission inventories.
The methods to measure miscellaneous secondary particles were also discussed. Inorganic compound such as sulphate, nitrate and chloride are analysed after water extraction with ion chromatography. Carbonaceous component is divided into organic carbon (OC) and elemental carbon (EC), the latter is considered inert and invariable in atmosphere. Thermal-Optical method is adopted for the OC/EC analysis. Other prevalent instrument such as GC/MS is also introduced to measure different SOA. In the end, control strategies of secondary PM2.5 were discussed.
KEYWORDS
Secondary PM2.5, VOCs, OC/EC, reaction mechanism, measurement method, control strategy
ACKNOWLEDGEMENT
This work is supported by the National Basic Research Program of China (grants 2009CB219802), the National
Science Foundation (51206144), the Natural Science Foundation of Zhejiang province (LY12E06003), and the
Program of Introducing Talents of Discipline to University (B08026).
1

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
1. INTRODUCTION
Among all the atmospheric particulate matters, PM2.5, also called respiratory particles, refer to solid and liquid particulate matters with aerodynamic diameters no more than 2.5 μm. PM2.5, especially the secondary particles of it, has a significant impact on air quality. China has already become one of the most heavily polluted areas in the word, occupying 16 out of 20 cities of the heaviest pollution according to a report of WHO for the year 2006.
Among the 522 air-monitored cities here in China, 40% of them cannot reach the second-level Air Quality
Standard, with 66.9% urban population exposed to the off-standard air. More and more combined pollutions such as chemical smog and haze are appearing in cities of China.
Secondary particles of PM2.5 mainly transform from Volatile Organic Compounds (VOCs), SO
2
and NOx.
According to a statistics of China 2010, the emission profile of SO
2
amounts to 21851 thousand tons, with 12067 thousand tons of industrially emitted SO2, occupying 78%. mainly result from the combustion of fossil fuels.
Based on the same statistics mentioned, the primary sources for industrial SO2 are electric and petroleum industries, with emission profiles of 8898 and 6222 thousand tons respectively, contributing 52.6% and 36.3% of the total industrial SO2 emission [1] . SO2 and NOx from urban vehicles are the major reasons for combined pollutions in city areas, but the statistical data are still unavailable for emission inventory of vehicle-emitted
VOCs countrywide. More and more attentions are drawn to the role that VOCs play in the formation of photochemical pollutions, which is also a major problem heckling cities abroad. VOCs are the major precursors for PM2.5 secondary particles, and they are usually emitted in large amounts with complicated emission sources widely distributed, including incomplete combustion, evaporation of oil solvent, industrial process and etc. Table
1 shows the emission profile of VOCs of several major countries, indicating that the production and usage of industrial solvent and vehicles are the contributing emission sources for VOCs. Figure 1 shows the emission amounts of SO2 NOx and VOCs in China.
Table 1 Anthropogenic emissions of several countries and their respective weightings
Countries or areas
Emission of VOCs
(in million tons)
First emission source
Weighting
Second emission source
China
USA
23.11
12.8
Usage of products containing VOCs
——
43.8%
——
Vehicles
——
20.9%
——
California,
USA
0.776 Stationary area source 40% Vehicles 26%
European
Union
7.412
Solvent, product usage, commercial organization, family emissions and vehicles account for 76%
Japan 0.79 Painting 37.3% fuels (evaporating) 18.9%
Notes: The emission data for USA are collected from statistics of 2012, while others 2010.
2

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
Figure 1 Annually emission amount of SO2 NOx and VOCs in China
2. Formation principles of secondary particles
Generally, after emitted into the atmosphere from emission sources, primary pollutants go through complicated chemical and photochemical reactions, and finally form secondary particles under the combined actions of horizontal and vertical transportation and diffusion, gaseous chemical transformations, cloud liquid processes, equilibrium and coagulation of aerosol production, dry and wet subsidence and many other factors.
2.1 Photochemical reactions of VOCs in atmosphere
According to statistics of 2005, alkane, unsaturated hydrocarbon, benzene series account for 20%, 21%, and 30% respectively in the VOCs emission of China. Usually, Reactive Organic Gases (ROGs) are those VOCs with transformation efficiency more than 10% under the current concentration of atmospheric oxidants. Anthropogenic
ROGs mostly come from off-gas of vehicles, such as benzene series, phenols, diolefines. Volatile aromatic compounds are the leading anthropogenic precursors for Secondary Organic Aerosols (SOA), 50%~70% SOA in the urban air come from benzene or its derivatives [2] . For gaseous organic compounds, transformations into SOA take places through two steps: the first is the gaseous reactions between ROGs and •OH, NOx, O3 and other atmospheric oxidants; the second is reversible distribution of semi-volatile secondary products between gas phases and solid phases. The formation of SOA is subjected to many factors such as other inorganic and organic components, temperature, light and humidity. Figure 2 shows the mutual transformation of free radicals in atmosphere [3] .
The transformations of aromatic compounds are started by reactions with •OH, where addition reactions play the major role and the dehydrogenation (replacing the substituent or the hydrogen atoms at C ⎯ H bonds of benzene) only makes up approximately 10% [4] . Take toluene as an example, the addition reactions between toluene and •OH are quite complex, for •OH can be added to ortho-position, meta-position, para-position and ipso–position, therefore form four different adducts. Two kinds of reactions including benzene conservation and benzene decomposition are followed as shown in Figure 3 [5] . With NO available, the major products of reactions between
OH-benzene adducts and O
2
are cresol, toluene oxide, butenedial, ethylglyoxal etc. For different position of the
O ⎯ O Bridge, the decomposition products can also be glyoxal and methylbutenedial. Jiang et al.
[6] and Kamens et al.
[7] discovered in the study of benzene reactions that the actual distribution modulus (K p
) of phenolic products is
3

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT) much higher than predicted, indicating that further reactions may continue in solid phase. The polymers formed by solid reactions of aldehydes (e.g., aldehyde reacts with alcohol and forms hemiacetal) will cause more parental aldehydes to enter solid phase, consequently increase SOA.
O
3 photolysis
O( 1 D)
NO
O
2
RO
2
RO
HO2
NO
O( 3 P) daytime
O
3
+HC
VOC+O
2
H
2
O
CO+O
2
O
3
·OH
O
3 photolysis photolysis
O
3
+peroxide or aldehydes
NO
2 heterogeneous reaction
O
2
NO
3
NO
2 photolysis
HONO
N
2
O
5 photolysis
VOCs aerosol
• OH
O
2
HNO
3 nighttime
O
3
Figure 2 Mutual transformations of free radicals in the atmosphere
Also photochemical oxidations, cyclic diene and aliphatic diene react into dicarboxylic acid, is the focus in
SOA studying [5,8] . For other ROGs such as alkane in the atmosphere, they mostly react with •OH during daytime, and with NO
3
radicals during nighttime at relatively slow reaction rate [9,10] . Above two kinds of reactions both undergo principal steps of dehydrogenation and transformation into alkyl radicals, which will be quickly oxidized into RO
2
. The major difference is that nitrate groups might decompose and form NO
2
in later reaction [11] . While reactions between alkene and OH radicals are firstly through addition reactions at C=C bonds and dehydrogenation at C-H bonds of alkyl substituent, and addition reactions play a major part in the small-molecule noncyclic alkene.
For ROGs reactions in the second step, it is generally assumed that organic compounds will condense only when the concentration exceeds its saturated vapour pressure, meaning that SOA will be formed by molecular homogeneous nucleation. However, follow-up studies found that ROGs would also enter the solid phase through adsorption, dissolution or absorption even when their gaseous concentration had not reached the saturated state Ошибка! Закладка не определена.
. Adsorption theory indicates that adsorptive capacity correlates with specific surface area; while absorption theory indicates that gaseous organism enters the solid phase by absorption and dissolution, and maintains the balance of absorption and desorption with its absorptive capacity proportional to the mass of aerosols. PAHs and other organic matter with low polarity is primarily guided by absorption principles.
Besides this, solid reactions of aerosols can never be omitted. When the reaction time is shorter than the life
4

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT) cycle (4~7 days) of particles in the flow laver, solid-phase reactions including accretion reaction [12,13,14] and aerosol aging [15,16] must be paid attention.
CH
3
CH
3
CHO
CH
2
ONO
2
OH
+HO
2
O
O
2
CH
2
·
NO
2 *
CH
3
CH
3
OH
·OH
Abstraction
·OH
Addition
H
H
+O
2
CH
3
CH
3
CH
3
O
O OH OH
NO
2
O
O
H
+O
2
O
O
H
H H O
NO
OH
H
+O
2
H
H
O
H
+
O
O
H
O O
CH
3
O O
H
Figure 3 Reaction pathways for the reaction of ⋅ OH with toluene
2.2 Photolysis of Vehicle-emitted NOx
NOx mainly comes from emission of motors, and its concentration is higher in urban areas with heavy off-gas pollution. NOx in the convection layer can directly undergo photolysis by absorbing sunlight with wavelengths of
290~700nm [17] .
2
 
2
*
(excited phase) 400~700nm (1)
2
 
 
290~420nm (2)
 
2

3
(M=air) (3)
3

2 2
(4)
5

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
M in above formulas are energy absorption molecules (usually O
2
and N
2
). The rate of photolysis of NO
2
is rather high, and therefore NO
2 can be decomposed into NO and O( 3 P) atoms by sunlight in relatively short time; afterwards O( 3 P) reacts with atmospheric oxygen immediately and ultimately forms O
3
. If the convection layer is clean enough, the reactions mentioned above will only undergo one cycle; in the presence of VOCs, one of the pathways will be hampered by NOx reactions, resulting in the continual increase of NO
2
and O
3
, and decrease of
NO.
Nitrous acid HONO is formed by heterogeneous reactions of NOx during nocturnal time, and later in the next morning, photolysis of HONO happens under sunlight. Two possible photolysis reactions of HONO are as follows [18] :
  
2
(5)
HONO+ h
   (λ=300~390nm) (6)
If air is wet, HONO can be hydrolyzed into NO
3
, and finally be turned into nitrates such as NH
4
NO
3
.
Multi-phase reactions of NOx on mineral surface have become the focus of recent studies. Börensen et al.
[19] put forward the formation principles of NO
3
with active OH on surface of Al
2
O
3
particles.
2.3 Process of formation of secondary particles in industrial SO
2
SO
2
mainly comes from industrial combustion of fossil fuels, and the formation of sulfates includes: oxidation of clouds and liquids and heterogeneous reactions with other aerosols [20] , while the principles of heterogeneous reactions remain uncertain. Mineral dust is the major components of land aerosols, and accordingly the important pathway for sulfate formation in the inland is the heterogeneous reactions of SO
2
on mineral dust. Usher at al.
[21] took advantage of infrared transmission spectrum to study the reactions of SO
2
on the surface of oxidants and found that O
2
and OH were involved as follows:
（ ） （ ）
2

3
（ ）
(7)
-

3
-
(8) or
（ ） 
SO
3 a +H O (9)
SO
3
2 and HSO
3
on the surface of oxidants are partially oxidized into SO
4
2 under the interactions of oxygen and adsorbed water, realizing the transformation from gaseous SO2 to solid SO
4
2 particles.
3. Modelling methods of secondary particles
For the complexity of formation mechanism, reaction mechanism of VOCs and theories of secondary aerosol nucleation progress still need perfection. Receptor models compute respective contributions of emission sources to receptors without chemical mechanism, and have been widely used since it came out in the 1970s.
3.1 Chemical Mass Balance (CMB) model
6

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
Chemical Mass Balance model is one of the most typical receptor models, equation of mass conservation is as follows:
C i
 n  j

1 f S ij j
 e i
(10)
Where j =1, 2, 3, …… , n, C i
refers to the concentration of component i in the atmospheric particulate matter. f ij
is the measured value of component i in the source j , S j
is the concentration contribution of source j , j is the number of sources, i is the number of elements, while e i
stands for the correction term. In the above formulas, S j
is the ultimate variable that needs to be calculated.
The total concentration at the receptor site is the linear sum of contribution from each source. CMB is widely applied in modelling contribution factors of key emission sources in municipal and rural places, such as motor emissions, industrial coal combustion, and biomass combustion. The chemical mechanism of organic particles is relatively simple: SO
2
and NOx from combustion of fossil fuel and municipal solid waste and NH
3
from fertilizer and agriculture react in the atmosphere and produce sulfates and nitrates. Chen at al.
[22] integrated data from
Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciation Trends Network (STN), applied CMB into source apportionment in typical municipal and rural places in USA, and introduced the concept of Effective Variance. The result showed that the percentage of sulfates and nitrates in PM2.5 is approximately
49~71%. With regard to organic particles, receptor models with organic tracers are usually chosen to identify the diffusion process of organic matter with several designated tracers, and CMB are employed in subsequent steps.
Perrone et al.
[23] modelled with CMB for northern Italian city of Milan and found a good agreement between modelling and measured results, using levoglucosan as the tracer for wood burning to study the contribution of wood burning in winter to organic pollutants. Contribution rates from secondary particles can also be identified with receptor models, but constituent spectrum has to be established first to identify tracer matter. Atoms that can be used as tracers in source apportionment are still limited, and therefore the method is still in the embryonic stage.
3.2 Positive Matrix Factorization (PMF) model
Positive Matrix Factorization (PMF) employs weighting factors first to identify the errors in the chemical components of particulate matters, and then nails down primary sources and their contribution rates using the method of Least Squares. Compared with CMB, it does not require the detailed information of source components, and therefore avoids the deviation resulting from the uncertainty of identified sources and the lack of unknown sources. However, large quantities of data are needed for this method, for they are the determinants of solution.
Acquisition of highly synthetic data requires a monitoring network that operates continuously and analytical ability to monitor different components of atmospheric particles with high quality. In the report of PM2.5 distribution characteristics in St Louis, Kim et al.
[24] introduced PMF analytical method in detail, using algebraic standard error to demonstrate time distribution patterns and Coefficients of Divergence (COD) to demonstrate the difference in distribution behaviours of particles in different areas. In the modelling process of PMF, strengthening the chemical analysis of secondary aerosols is the effective way to improve the modelling accuracy and extend the receptor analysis of SOC in PM2.5.
3.3 CMAQ model
Receptor models calculate with statistics or coupled algorithms, which lack mechanism modelling of photochemical processes in the atmosphere. Models-3 air quality system, which is put forward by US EPA, is
7

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT) based on the “one atmosphere” principle and takes many factors in one single coordinate system. It realizes the highly accurate modelling of a certain region by virtue of drawing small grids, and is typically composed of MM5 model which models physical aerodynamics, SMOKE model which pre-processes emission inventories, and
CMAQ model which simulates chemical transportation. CMAQ model is the central part of air quality systems, and its conservation equation is as follows [25,26] :
.
 c i
 t
    
D i
 c
 i
 i

1 2
,
, c T t n
  i
( , ) (11)
Where i =1, 2, 3, …… , n, c i
is the concentration of component i , U is the velocity vector of wind, D i
is the molecular dispersion coefficient of component i , R i
is the rate of concentration variation in the chemical reaction,
S i
(x,t) is the magnitude of source of component i at coordinate x and at time t , ρ stands for air density, n stands for number of assumed components in the model. The equation describes the formation, transportation and evolution of components, with processing of constituents, meteorological conditions and atmospheric chemistry all included.
In CMAQ 4.7, Carbon Bond mechanism (CB05), updated in 2005, is employed to calculate input inventory such as VOCs and PM2.5, and moreover isoprene, sesquiterpenes, benzene, glyoxal and methylglyoxal are added to the precursors of secondary aerosols in the model. In previous versions of CMAQ, all SOA was treated as semi-volatile. In CMAQv4.7, four types of nonvolatile SOA are simulated.
Pay et al.
[27] simulated time and spatial distribution of particles in Spain. It set 4km×4km grids, and got
397×397 grids in total. The paper evaluated total emission of PM2.5 and carried out source apportionment of salt aerosols, inorganic ions and other emitted particulate matter. Observation revealed that modelling results were in good agreement with studies of other researchers. The biggest advantage of CMAQ is that it introduces the latest atmospheric chemistry and photochemical mechanism, and significantly improves the accuracy by modelling all factors under one atmosphere in the unified coordinate system. Marmur et al.
[28] applied both CMAQ and CMB models to study the health effect of PM2.5 in southern USA, and found that CMAQ was superior in the modelling regional distribution by comparing the two results. We have to pay attention to the fact that as the most crucial precursor of SOA, VOCs have extremely complicated components and reaction mechanisms still to be studied, and therefore suitable chemical principles have to be chosen according to specific emission characteristics in applying CMAQ, meanwhile it is necessary to compare the result with CMB model.
4. Measuring principles and methods of secondary particles
PM2.5 secondary particles include various sulfates, nitrates and SOA. Measurements include quantitative analysis of particle components and inspection of tracers in secondary reactions. Secondary organic matters are usually measured with Organic Carbon (OC) method. It assumes that element carbon (EC) originates from combustion, and stays inactive in the atmosphere as primary particles. OC/EC in primary particles of a specific region is fixed, and therefore if measurement shows that the actual ratio exceeds the value, it means that there are extra OC emerged, and we treat this part of OC as SOA. SOC can be approximated using the following formula [29] :
sec

tot

pri
(12)
Where OC sec is secondary organic particles, OC tot
is the total carbon measured, EC is element carbon, and
(OC/EC) pri
stands for the ratio of primary organic carbon to element carbon.
4.1 Thermal-optical method
8

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
Thermal-optical method is widely recognized as a method for analysing SOC. Let a laser beam transmit a filter membrane which adsorbs organic particles, and the absorption rate of element carbon and transmission rate of the laser can be used to infer the variation of carbonaceous component qualitatively. This method is often termed
Thermal-Optical Transmission (TOT). Yin & Harrison [30] applied this method to analyze OC in urban and rural atmospheric particles and their experimental procedures are as follows:
Heat quartz-fiber membrane with organic matters from ambient temperature to 700 ℃ under non-oxidant atmosphere (helium atmosphere, during which process partial decomposition of OC and carbonization take place), and let the decomposition products pass through MnO
2
oxidation furnace blown by the carrier gas helium, and then mix up the oxidant products CO
2
and H
2
with catalysts for the formation of CH
4
. CH
4
can be finally identified quantitatively with Flame Ionization Detector (FID). The next step is to heat filter membrane under the mixed atmosphere of helium and O2 from 550 ℃ to 850 ℃ , during which process the remaining carbon will be oxidized to CO
2
and then be transformed into CH4 with H
2
for FID detection. Throughout the whole process, a laser beam is projected onto the filter membrane. The laser intensity changes during this progress, and when transmission intensity comes back to the original value, the point it reaches is the breakpoint of OC and EC.
If we correct the breakpoint of OC and EC with optical reflection, it is Thermal-Optical Reflection (TOR). The breakpoint is the key to differentiate between these two methods. Figure 4 illustrates the principle of TOT and
TOR. Cheng et al.
[31] analysed 333 samples in southern USA with TOT and TOR respectively, and results indicated that the two methods were comparable in terms of total carbon measurement, but the TOT obtained a slightly higher value of 10-20% than TOC. It is reported that the breakpoint of TOR comes before that of TOT, and the reason lies in the fact that oxidation takes place from outside to inside for particulate matters on the surface of quartz filter membrane. Due to the adsorption of membrane, when OC evaporates in the non-oxygen environment with high temperature, it will be first absorbed into the depth of membrane and then start to split. The decomposed carbon in the depth will only result in the decrease of transmitted light, with no effect on the reflection intensity. Thus, the reflected intensity will restore its original value ahead of transmitted intensity, leading to the earlier arrival of the breakpoint for TOR, consequently causing the value of EC greater and the value of OC smaller. Chow et al.
[32] pointed out that difference in the pyrolysis temperature will also bring about different results.
9

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
Laser reflectance detector
Laser(632nm)
Quartz light pipe
Deposit side of 0.5cm
2 quartz filter
Sample oven with heater Pushrod
CH
4
← CO
2
Reducer
(Methanator)
CO
2
← C
Oxidizer
(Oxidation Oven)
Quartz light pipe
Gas flow direction
Combustion at 100% He
Flame
Ionization
Detector
(FID)
Laser transmittance detector
Thermocouple
Figure 4 Experimental configuration for thermal/optical reflectance (TOR ) and thermal/optical transmission carbon analysis
4.2 Ion Chromatography (IC) and GC-MS
Inorganic matters are the major constituent of PM2.5, among which NO
3
- and SO
4
2 need to be measured in particular using Ion Chromatography [33] . The components of VOCs are extremely complicated, with aromatic alkane, other alkane and alkene playing the major role in anthropogenic VOCs. GC-MS with high resolution has good application in separating and testing SOA. Duan Fengkui and He Kebin [34] of Tsinghua University measured
PM2.5 SOA in Beijing with GC-MS, fulfilling the entire separation among normal alkane, polycyclic aromatics and organic acid ester.
Table 2 Comparison between IC and GC-MS
Measurement methods
Measurement objects
Ion Chromatography
Cl , NO
3
, SO
4
2, Na + , NH
4
+ , K + ,
Mg
2
+ , Ca
2
+
Sampling, Pre-processing and anion
GC-MS
VOCs such as: normal alkane, polycyclic aromatics and organic acid ester
Instrument and equipment, Processing of samples, instrument analysis
Main steps
Concentration range
Characteristic measurement, Analysis and checkout
1 ～ 10μg/L
Off-line
5 Control technologies of secondary particles
10
10 -10 g
Off-line

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
The crux of secondary particles removal lies in reducing the emission of precursors. In China air quality control has always centred on dealing with dusts, SO
2
and NOx, with insufficient attention to controlling VOCs.
Therefore most industrial emission sources of VOCs haven’t been regulated up to now. The following passages mainly focus on introducing control technologies of VOCs.
5.1 VOCs control technologies
Basic ideas of source-tracing are used in our country [35] . The method studies emission of VOCs according to its flow in social production activities. Emissions of VOCS happen through the whole process of production, transportation and storage, technical process of manufacture from VOCs, usage and disposal of products containing VOCs. The mainstream control techniques at home include: adsorption, catalytic combustion, thermal incineration and biological technologies, among which adsorption technique makes up for over 50%, and catalytic combustion technique accounts for about 30%. Compared to other treatment, adsorption has the characteristics of high purification efficiency, simple equipment and low investment, and is the most widely applied [36] .
5.2 Control measures of reducing emission of secondary particles [37]
5.2.1 Establishing emission factors of SO
2
, NOx and VOCs for domestic sources and complementing pollution inventories
Emission factor, which requires nearly comprehensive data, is one principal method used in European and
American countries to estimate total pollution emission, and is recently popularly used here in China. Due to the late establishment of inventory in China, data concerning emission factors of all types of sources are still lacking, and therefore data abroad is commonly applied with correction to different situations. However, different production conditions and social-economic development levels will lead to huge discrepancy between emission factors and actual emission, thereby necessitating the establishment of emission factors based on domestic fuel consumption and treatment level is currently the main task.
5.2.2 Framing emission standards and control policy for all sectors, identifying key targets for emission reduction and inciting innovation of pollutant control
The monitor and study on pollutants start late in China, in addition, emission levels varies significantly in different places, so it is hard to build an effective way to restrict emission. The key is to establish industrial emission standards corresponding to the national conditions and eliminate outdated production and emission reduction techniques. Seminars have been launched to set new standards for SO2 and NOx, but there is still a long way to go for VOCs. We have always been the leading emitter in the world, and the total emission of VOCs is far greater than that of SO
2
and NOx, hence the control policy of VOCs should include: setting up emission standard of VOCs for related industries, assessment system of clean production and technical regulation of treatment; speeding up the establishment of standard measurement, technical regulation of monitor and standard of monitoring instruments for air quality and VOCs from fixed sources; establishing admission regulations for sale and usage of organic products, enforcing control on threshold of VOCs content in products, and building declaration system of organic solvent usage for major industries.
5.2.3 Strengthening monitoring of pollutants by virtue of complementing regulating list of SO
2
, NOx and VOCs
11

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
Anthropogenic emission of SO
2
, NOx and VOCs is concerned with all aspects regarding industrial and agricultural production. SO
2
and NOx mainly come from industrial and traffic combustion of fossil fuels; the sources for VOCs are rather complex and disperse widely. So it is of great importance to regulate key emission sources, set up regulating list for areas and companies with heavy pollution and launch integrated pilot program of pollution control for reducing pollutant emissions.
6 SUMMARIES
The study on atmospheric secondary particles is closely related with our life. Due to the intricate content of atmospheric particles, approach is still unavailable for complete differentiation between primary and secondary aerosols. Recently, there has been a trend to carry out source apportionment from precursors which include VOCs,
NOx and SO
2
. The attention has been paid to NOx and SO
2
owing to issues of acid rain. Strict limitation has been enforced since Chinese 11th five-year plan, and the policies need to be carried on strictly to alleviate pressure that industrial production exposes on the environment, especially in light of the enormous base value of our emission.
The study on VOCs emission is still in the early stage, and basic data are still unavailable, necessitating the establishment of studying measures of VOCs based on our national conditions. The summary is concluded on three aspects as follows:
6.1 Enhancing the mechanism studies on photochemical reactions with VOCs in the atmosphere
With the deepening of studies on atmospheric reactions, our understanding on characteristics and formation mechanism of SOA has been greatly improved. However, studies till now have only been concentrated on reaction mechanism of specific gas precursors without taking the influence of secondary products into consideration, and moreover there are still many limitations on particulate-phase aerosol reactions. Some substance is highly active and therefore can only exist for a short time in the atmosphere, causing difficulty in identifying its content and reaction mechanism. Due to the damage caused by analytical techniques, problems arise for the identification of some trace-amount SOA. Smoke chamber is one important way to study secondary reactions. It can simulate photochemical reactions by controlling parameters such as temperature, pressure, sunlight, humidity and wind speed. Online monitoring technology makes it possible to monitor the real-time variation of content and concentration in the reaction chamber, and therefore the method should be greatly promoted. Molecular tracer method is an important way to establish organic content of pollution sources. We should build up data pool of organic content for typical sources, enlarge the lists of organic tracers and develop and complement its application in source apportionment.
6.2 Localizing Model-3 and employing CMAQ to domestic environmental decision-making
Model-3 simulates all factors including meteorology, geography and chemical principles under one single system, and is highly credible with accurate distribution in three dimensions. In Model-3 system, emission sources are simulated according to the resolution of American inventory. The very first step is to localize Models-3 due to its strict requirements of gridded inventory. The job of localization includes new classification of inventory, establishment of accurate emission factors, real-time monitor of key emission sources, establishment of
3-dimensinal data set for domestic atmosphere and etc. Pearl River Delta is one of areas covered by perfect air monitoring network, and localization of Modes-3 has been initiated there. It is therefore crucial to take Pearl River
Delta as a reference to set up modelling and monitoring network to cover major regions, or even the whole nation.
12

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
6.3 Expediting establishment of domestic emission inventory of VOCs
The emission of VOCs of our country has far exceeded that of SO
2
and NOx and has become one contributing factor affecting urban environment. European and American countries have many experience and advances in studying VOCs emission, and we are still borrowing their method of emission factor. However, considerable errors arise due to the discrepancy of technical levels and national conditions between our country and western countries. The suggestion is that we expedite the complement of emission factors of VOCs, employ source-tracing method for analysing emission data, restrict avoidable errors in the estimation, and provide inventory support for
Models-3 application.
REFERENCES
[1] 盛来运 . 中国统计年鉴 : 2011[J]. 2011.
[2] Odum J R, Jungkamp T P W, Griffin R J, et al. Aromatics, reformulated gasoline, and atmospheric organic aerosol formation[J]. Environmental science & technology, 1997, 31(7): 1890-1897.
[3] Sadanaga Y, Matsumoto J, Kajii Y. Photochemical reactions in the urban air: Recent understandings of radical chemistry[J]. Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2003, 4: 85-104.
[4] Yao L, Ge M F, Qiao Z M, et al. Progresses of tropospheric chemistry of volatile organic compounds[J].
Chemistry Bulletin, 2006, 69(W049): 1-7.
[5] Bai Z, Li W. Characteristics and Formation Mechanism of Secondary Organic Aerosol[J]. Chinese Journal of
Process Engineering, 2008, 8(1): 202.
[6] Jang M, Kamens R M. Characterization of secondary aerosol from the photooxidation of toluene in the presence of NO x and 1-propene[J]. Environmental Science & Technology, 2001, 35(18): 3626-3639.
[7] Kamens R M, Jaoui M. Modeling aerosol formation from α-pinene+ NO x in the presence of natural sunlight using gas-phase kinetics and gas-particle partitioning theory[J]. Environmental science & technology, 2001, 35(7):
1394-1405.
[8] Jacobson M C, Hansson H C, Noone K J, et al. Organic atmospheric aerosols: Review and state of the science[J]. Reviews of Geophysics, 2000, 38(2): 267-294.
[9] Atkinson R, Arey J. Atmospheric degradation of volatile organic compounds[J]. Chemical Reviews, 2003,103:
4605-4638.
[10] Penkett S A, Burgess R A, Coe H. Evidence for large average concentrations of the nitrate radical (NO3) in
Western Europe from the HANSA hydrocarbon database[J]. Atmospheric Environment, 2007,41: 3465-3478.
[11] Zhou Y, Xu J, Chen H, et al. Research progresses in the chemistry of secondary organic aerosols[J]. Sichuan
Environment, 2013 (1): 110-117.
[12] Kroll J H, Seinfeld J H. Chemistry of secondary organic aerosol: Formation and evolution of low-volatility organics in the atmosphere[J]. Atmospheric Environment, 2008, 42(16): 3593-3624.
[13] Garland R M, Elrod M J, Kincaid K, et al. Acid-catalyzed reactions of hexanal on sulfuric acid particles:
Identification of reaction products[J]. Atmospheric Environment, 2006, 40(35): 6863-6878.
[14] Zhao J, Levitt N P, Zhang R, et al. Heterogeneous reactions of methylglyoxal in acidic media: Implications for secondary organic aerosol formation[J]. Environmental science & technology, 2006, 40(24): 7682-7687
[15] Kroll J H, Ng N L, Murphy S M, et al. Secondary organic aerosol formation from isoprene photooxidation[J].
Environmental science & technology, 2006, 40(6): 1869-1877.
[16] Walser M L, Park J, Gomez A L, et al. Photochemical aging of secondary organic aerosol particles generated from the oxidation of d-limonene[J]. The Journal of Physical Chemistry A, 2007, 111(10): 1907-1913.
[17] Zhenya W, Liqing H, Weijun Z. Chemical Processes on the Formation of Secondary Organic Aerosols[J].
PROGRESS IN CHEMISTRY-BEIJING-, 2005, 17(4): 732.
[18] Jianmin Y X C. Advances in the Mechanism of Secondary Fine Particulate Matters Formation[J]. Progress in
Chemistry, 2009: Z1.
13

International Conference on Air Pollution Control Benefit and Cost Assessment ICAPC2013 (ABSTRACT)
[19] Börensen C, Kirchner U, Scheer V, et al. Mechanism and kinetics of the reactions of NO2 or HNO3 with alumina as a mineral dust model compound[J]. The Journal of Physical Chemistry A, 2000, 104(21): 5036-5045.
[20] Wu H, Chen J, Xue H, et al.Heterogeneous reaction of sulfur dioxide with atmospheric particles[J]. The
Chinese Journal of Process Engineering, 2004, 8.
[21] Usher C R, Al ‐ Hosney H, Carlos ‐ Cuellar S, et al. A laboratory study of the heterogeneous uptake and oxidation of sulfur dioxide on mineral dust particles[J]. Journal of Geophysical Research: Atmospheres (1984 –
2012), 2002, 107(D23): ACH 16-1-ACH 16-9.
[22] Chen L W A, Watson J G, Chow J C, et al. PM2. 5 Source Apportionment: Reconciling Receptor Models for
US Nonurban and Urban Long-Term Networks[J]. Journal of the Air & Waste Management Association, 2011,
61(11): 1204-1217.
[23] Perrone M G, Larsen B R, Ferrero L, et al. Sources of high PM2. 5 concentrations in Milan, Northern Italy: molecular marker data and CMB modelling[J]. Science of the total environment, 2012, 414: 343-355.
[24] Kim E, Hopke P K, Pinto J P, et al. Spatial variability of fine particle mass, components, and source contributions during the regional air pollution study in St. Louis[J]. Environmental science & technology, 2005,
39(11): 4172-4179.
[25] Byun D, Schere K L. Review of the governing equations, computational algorithms, and other components of the Models-3 Community Multiscale Air Quality (CMAQ) modeling system[J]. Applied Mechanics Reviews,
2006, 59(1/6): 51.
[26] Binkowski F S, Roselle S J. Models ‐ 3 Community Multiscale Air Quality (CMAQ) model aerosol component 1. Model description[J]. Journal of Geophysical Research: Atmospheres (1984 – 2012), 2003, 108(D6)
[27] Pay M T, Jiménez-Guerrero P, Jorba O, et al. Spatio-temporal variability of concentrations and speciation of particulate matter across Spain in the CALIOPE modeling system[J]. Atmospheric Environment, 2012, 46:
376-396.
[28] Marmur A, Park S K, Mulholland J A, et al. Source apportionment of PM2.5 in the southeastern United States using receptor and emissions-based models: Conceptual differences and implications for time-series health studies[J]. Atmospheric Environment, 2006, 40(14): 2533-2551.
[29] Ye W, Wu L, Feng Y, et al. Advances in the estimation methods of secondary organic aerosol in atmospheric environment[J]. Journal of Safety and Environment, 2011, 11(1): 127-131.
[30] Yin J, Harrison R M. Pragmatic mass closure study for PM1.0, PM 2.5 and PM10 at roadside, urban background and rural sites[J]. Atmospheric Environment, 2008, 42(5): 980-988.
[31] Cheng Y, Zheng M, He K, et al. Comparison of two thermal-optical methods for the determination of organic carbon and elemental carbon: Results from the southeastern United States[J]. Atmospheric Environment, 2011, 45:
1913-1918.
[32] Chow J C, Watson J G, Chen L W A, et al. Equivalence of elemental carbon by thermal/optical reflectance and transmittance with different temperature protocols[J]. Environmental Science & Technology, 2004, 38(16):
4414-4422.
[33] Park S S, Kim Y J. Source contributions to fine particulate matter in an urban atmosphere[J]. Chemosphere,
2005, 59(2): 217-226.
[34] Duan F, He K. Extraction ， Separation and Purification of Three Kind of Organic Species in Atmospheric
Particulate Matter and the Measurements by GC/MS[J]. Journal of Chinese Mass Spectrometry Society, 2010,
31(3): 165-171.
[35] Ye D Q. Studies on Anthropogenic Emission Characteristics and Trends of Volatile Organic Compounds in
China [R]. PRC, South China University of Technology, 2011.
[36] 栾志强 . 中国工业 VOCs 治理现状、 [R]. PRC, 中国环境保护产业协会废气净化委
员会 , 2011.
[37] Ning M, Xue W B. Thoughs & Policy Recommendations on Prevention & Treatment of VOCs Emission during the 12th FYP. [R]. PRC, Chinese Academy for Environmental Planning, 2011.
14