There has been controversy regarding the air pollutants emitted from sources
closely related to the activities of daily life in China, such as cooking, setting off fireworks,
sacrificial incense and joss paper burning, and barbecue (which have been named the five
missing sources – FMSs), and the extent to which they impact the outdoor air quality. To date, due to the
lack of both an activity dataset and emission factors, there have been no estimations of the emission of air pollutants from FMSs. In this work, we have attempted to
combine questionnaire data, various statistical data, and data on points
of interest to obtain a relatively complete set of activity data. The
emission factors (EFs) of carbonaceous aerosols were tested in our lab.
Emission inventories of carbonaceous aerosols with a high
spatial–temporal resolution for FMSs were then established, and the
spatial variation trend and driving forces were discussed. From 2000 to
2018, organic carbon (OC) emissions were in the range of 4268–4919 t.
OC emissions from FMSs were between 1.5 ‰ and 2.2 ‰ of the total
emissions in China. Black carbon (BC), elemental carbon (EC), and
brown carbon (BrC) absorption cross-section (ACS
China has experienced a period of serious air pollution, which has had serious health impacts on residents (Zheng et al., 2018; Q. Zhang et al., 2019; L. Zhang et al., 2020a; Tong et al., 2020). Carbonaceous aerosols (CAs), emitted from incomplete burning, include organic carbon (OC) and black carbon (BC) or elemental carbon (EC), and these species have attracted wide attention due to their adverse impacts on air quality, human health, and climate (Venkataraman et al., 2005; Ramanathan and Carmichael, 2008; Bond et al., 2013). The optical properties of CAs (especially brown carbon, BrC) are complex and mutative, which is also one of the important factors affecting the global radiation balance (Feng et al., 2013; Laskin et al., 2015).
Several sources closely related to traditional human activity are
potential emission sources of CAs, such as the burning of sacrificial incense
and joss paper, traditional Chinese barbecue, Chinese-style cooking, and
fireworks. The estimation of air pollutant emissions from these sources has been
omitted from existing emission inventories; thus, they have been defined as the “five
missing sources” (FMSs) in this study. The FMSs can lead to a dramatic impact on the
ambient air quality and human health over a short period or in a specific region
(Chiang
and Liao, 2006; Wu et al., 2015; Kong et al., 2015; Ho et al., 2016; Wang et
al., 2017; Lai and Brimblecombe, 2020). For example, fireworks have been shown to
contribute 60.1 % of PM
In China, the differences in population and economy between urban and rural areas are increasing (Meng et al., 2019), and the efficiency of and necessity for air quality control policies for the FMSs in urban and rural areas need to be assessed. For instance, fireworks are generally banned in central urban regions, whereas the suburbs and rural regions are less affected by such policies. Moreover, cooking smoke needs to be purified in city centers, whereas this policy may not be strictly executed or even necessary in suburban and rural areas. Such deviation in the establishment and implementation of policies could ultimately drive the differences in air pollutant emission distributions; however, these differences have not yet been addressed.
Emission inventories are the foundation of a quantitative description of anthropogenic pollutant emissions (Li et al., 2017). The combination of chemical transport models and high-resolution emission inventories has been paramount for understanding the impact of anthropogenic perturbations on the atmosphere and for assessing corresponding air pollution control strategies (Janssens-Maenhout et al., 2019; McDuffie et al., 2020). The lack of emission inventories has limited large-scale model simulations, the optimization of corresponding control measures, and the settlement of related disputes. In our previous work (Wu et al. 2021), we established an emission inventory of levoglucosan that included emissions from the FMSs (Wu et al., 2021). However, to the best of our knowledge, no other emission inventories of the FMSs have been reported.
In summary, this study aimed to develop a methodological framework for
establishing an emission inventory of the FMSs, including methods for the acquisition of various
activity data, emission factor monitoring, uncertainty
assessment, and spatial–temporal allocation. The activity data were obtained
based on household investigation, statistical data, and points of interest (POI),
among other sources. The emission factors were monitored using a unique emission
monitoring test platform, especially for fireworks, in our lab. A high spatial (
The combustion tests for the FMSs were performed using two custom-made combustion chambers: one of them had an explosion-proof function and was used in firework burning experiments, and the other was used in the sacrificial incense, joss paper, barbecue, and cooking emission experiments. A dilution sampling system (FPS-4000, Dekati, Finland) was employed to dilute the smoke. The smoke samples were diluted about 16–30 times and aged for about 30 s in a residence chamber. This sampling system has previously been utilized in residential fuel combustion experiments (Cheng et al., 2019; Yan et al., 2020; Y. Zhang et al., 2021; Wu et al., 2021). A total of 38 events were tested in this experiment: 6 trials of sacrificial incense combustion (including red incense – RI, environmental incense – EI, and high incense – HI), 6 trials of joss paper burning (including red-printed paper – RP, small sacrificial paper – SP, and large sacrificial paper – LP), 10 trials of fireworks (including firecrackers – FC, fountain fireworks – FF, handheld fireworks – HF, handheld fountain – HT, and spin fireworks – SF), 8 trials of barbecue (including chicken – CK, beef – BF, lamb – LB, and pork – PK), and 8 trials of cooking (including cooking of meat – MT1, cooking of meat and pepper – MT2, cooking of meat and garlic – MT3, and cooking of meat, pepper, and garlic – MT4). The materials used in the experiments are shown in Fig. S1.
After dilution, the OC and EC in the smoke samples were detected with an online CA analyzer developed by the Key Laboratory of Environmental Optics and Technology (Anhui Institute of Optics and Fine Mechanics, CAS) and based on the thermal–optical method (Ding et al., 2014). The analyzer showed reliable stability and repeatability. More details on the online CA analyzer can be found in Sect. S1. A dual-spot Aethalometer (Model AE33, Magee Scientific, USA) was employed to measure the BC concentration and particulate optical properties (Drinovec et al., 2015). The system used in the experiments is shown in Fig. S2.
The emission factors (EF, mg kg
All filter-based optical measurements suffer from an
underestimation caused by the loading effect
(Drinovec et al., 2015); however, loading
compensation can be calculated based on dual-spot measurements. The reader is referred to Drinovec et al. (2015) for the detailed calculation process. Inferior dependence
of BC particles on light absorption at different light wavelengths has been found. The
absorption Ångström exponent (AAE) is an exceptional parameter to
describe this dependence, as shown in Eqs. (2) and (3):
As shown in Eq. (5), the
Data on the activity of sources directly affect the uncertainties in the emission inventory, and an accurate estimate of the FMSs' consumption was a crucial prerequisite. Statistics on the direct consumption of the FMSs are scarce. Thus, multiple activity data and proxy variables have been adopted in this work, including the statistical yearbooks of each province in China, datasets of POI (Sect. S2, Fig. S3), and rural household investigation data (Sect. S3).
The original information on the consumption of sacrificial incense, joss paper, and fireworks
was obtained from household investigation; therefore, the information used was the per capita consumption of
sacrificial incense, joss paper, and fireworks in each province. The data
were adjusted to overcome the problem of insufficient sample size. In China,
“sacrificial activity” refers to honoring ancestors, and it mainly takes place
in temples or graveyards. China is a mountainous country with rolling
terrain. Most of the inhabitants of non-plain areas chose hills that might
be covered in vegetation as the site of graveyards. The data on the consumption of
sacrificial incense and joss paper were revised based on the number of
temples (from POI data) and the frequency of forest fires caused by sacrifices
compared with the total frequency of forest fires (from China Forestry Statistical Yearbook data),
as shown in Eq. (9):
The firework consumption amounts were revised based on the number of
retail shops selling fireworks (from POI data) and the provincial fireworks export
volume (statistical data), as shown in Eq. (10):
The original meat consumption information per capita was obtained from the statistical yearbook
of each province. However, the methods and radii of the various provincial
statistical yearbooks showed differences, and part of the municipal-level
statistics was missing. To complement the missing data, the municipal per capita
consumption expenditure was introduced. The logarithmic relationship between
the per capita consumption expenditure and the provincial per capita meat
consumption was adopted to complement municipal per capita meat consumption,
as shown in Eq. (12):
Some cities have established policies to forbid sacrificial incense,
joss paper, and firework burning in the main urban area; however, such policies
have been inoperative in nonurban regions. According to our survey, the policies
forbidding sacrificial incense and joss paper burning have been relatively vague. We also
assumed that if a city forbade fireworks, the burning of
sacrificial incense and joss paper would also be banned. The total emissions (
Emissions from barbecue were calculated as follows:
Emissions from cooking were calculated as the sum of the emissions from residential cooking
and emissions from the catering industry. They were calculated using Eqs. (15) and
(16), respectively:
A Monte Carlo simulation was employed to analyze the uncertainties in the emission inventory (Wu et al., 2018). The simulation was executed 10 000 times. The uncertainties in the activity data were set as 0.2 or 0.5 (Table S1), and the uncertainties in the EFs were obtained from actual measurements. The resulting uncertainties are shown in Table S2.
As mentioned above, rural and urban activity resulting in emissions of the FMSs might
differ greatly. During the process of spatial allocation, this difference
must be emphasized. We used geographic information system (GIS) data for the classification
of land use in order to divide regions into urban and nonurban areas
(Gong et al., 2019,
2020). Based on this method, we obtained the data on the population distribution
(data from
The temporal allocation methods for the FMSs were also specific. To calculate
the annual emission trends, statistical data including annual firework
sales (from Ministry of Emergency Management of
the PRC data) and annual restaurant sales (from
Methodological framework for establishing a high-resolution emission inventory for the five missing sources (FMSs).
The EFs obtained from the 38 tests are shown in Table 1. The mean EF
Black carbon (BC), organic carbon (OC), and elemental carbon (EC) emission factors for the five missing sources (FMSs) (in mg kg
The abbreviations used for fuels are as follows: RI – red incense; EI – environmental incense; HI – high incense; RP – red-printed paper; SP – small sacrificial paper; LP – large sacrificial paper; FC – firecrackers; FF – fountain fireworks; HF – handheld fireworks; HT – handheld fountain; SF – spin fireworks; CK – chicken; BF – beef; LB – lamb; PK – pork; MT1 – cooking of meat; MT2 – cooking of meat and pepper; MT3 – cooking of meat and garlic; and MT4 – cooking of meat, pepper, and garlic.
To quantify the light absorption properties of emissions from the FMSs, AAEs
(370–880 nm) were calculated (Fig. 2). The average AAEs of the FMSs were in the
range of 1.26–3.15. The mean AAE of sacrificial incense (2.69
The absorption Ångström exponents (AAEs; 370–880 nm) of the FMSs.
We have calculated the
Furthermore, the AEFs of BrC and BC have been calculated, as shown in Fig. S5. As the wavelength increased, the AEFs showed a decreasing trend. When
The total consumption of the FMSs is shown in Fig. 3. In 2018, 16.5, 919, and 5139 kt of sacrificial incense, joss paper, and fireworks were burned in China, and 30 996, 2872, 1920, and 12 057 kt of pork, beef, lamb, and chicken were consumed. The total consumption of the abovementioned FMSs amounted to about 26.4 % of the residential coal consumption in China (Peng et al., 2019). The burning of sacrificial incense, joss paper, and fireworks was highest in Shandong (394 kt) and Sichuan (470 kt). Except for lamb, Guangdong Province has the highest consumption of three kinds of meats (6197 kt); the province with the highest consumption of lamb is Xinjiang (361 kt). The consumption of the FMSs can be a reflection of the local customs. For example, lamb consumption in Xinjiang is the highest in China. The reason for this may be that Xinjiang is the main lamb-producing area and one of the five main pastoral areas in China, and the region's ethnic structure makes mutton a dominant part of the daily diet (Xu et al., 2018).
The total consumption of the FMSs in China during 2000–2018. The abbreviations used in the figure are as follows: SI – sacrificial incense, JP – joss paper, FW – fireworks, PK – pork, BF – beef, LB – lamb, and CK – chicken.
The consumption of the FMSs in most cities was found to be low. The top 30 cities
(about 8 % of the total number of cities) with the largest firework
consumption contributed 41.8 % of the national consumption (Fig. S6).
These cities have higher population densities, and control measures for
fireworks were not in place at the time of study. Per capita firework consumption in 52 %
of the cities was less than 5 kg yr
In 2000–2018, the OC, EC, BC, and BrC absorption cross-section (ACS
Total CA emissions from the FMSs in China from 2000 to 2018. The abbreviations used in the figure are as follows: SI – sacrificial incense, JP – joss paper, FW – fireworks, BBQ – barbecue, RC – residential cooking, and CI – catering industry.
There are seven geographical regions in China (Fig. S9); of these areas, East
China is the largest CA emission region, contributing
24.2 %–27.7 %, 23.9 %–29.6 %, 24.2 %–29.0 %, and 23.5 %–29.9 % of the
OC, EC, BC, and ACS
The emission distributions from different sources showed great differences,
which stemmed from the regional cultural and economic diversity (Figs. S10,
S11). High-emission regions with respect to sacrificial incense and joss paper burning
overlapped with areas with large numbers of temples and cradles of
Chinese Buddhism (Fig. S3, Sect. S7); people in these areas may be
more devout about sacrifice. The distributions of cooking emissions (both
residential cooking emissions and catering industry emissions) and barbecue
emissions were highly similar to the population distribution, especially in
urban regions. This is consistent with previous studies which reported that
cooking-related organic aerosol (COA) concentrations at urban sites
(6.46–6.97 in Beijing and 14.2
Spatial distribution of CA emissions from the FMSs in China in 2018. The color bar shows the emissions in each grid (where grid is denoted as Gd).
As shown in Figs. S12 and S13, CA emissions from residential sources
in winter were much higher than those in summer due to the heating
demand during the former season
(Wang
et al., 2012; Huang et al., 2015; Li et al., 2017), while emissions from the FMSs
showed a similar seasonal trend due to fireworks. During the
Chinese Spring Festival, fireworks result in massive pollutant
emissions and severe air pollution
(Kong
et al., 2015; Yao et al., 2019; Ding et al., 2019; Lai and Brimblecombe,
2020). We have investigated the CA emissions from the FMSs in each month and during
several related Chinese festivals (CNE, CSF, LF, QF, and ZF). As shown in
Fig. 6, emissions were mostly concentrated in January and February
(CNE and CSF are in the same month in 2000–2018); after the calculation
of multiyear data, the results for January and February in Fig. 6 seemed
to be lower than those in Fig. S13. A total of 75.8 % of fireworks were set off during
CNE and CSF, and 20.4 % were set off during LF (Fig. 7). Thus, the
ACS
Averaged monthly CA emissions from the FMSs in China for the period from 2000 to 2018.
Average CA emissions during Chinese New Year's Eve (CNE), the Chinese Spring Festival (CSF), the Spring Lantern Festival (LF), the Qingming Festival (QF), and the Zhongyuan Festival (ZF) for the period from 2000 to 2018. AVE shows the average daily emissions for periods outside of the festivals mentioned above.
For a short-term period, emissions from the FMSs also showed an obvious spatial
distribution. A total of 83.2 %–93.1 % of OC emissions came from barbecue and cooking.
The higher population density and living quality led to higher OC emissions
in urban regions. As shown in Fig. 8, the OC emission intensities (average
emission per grid) in the urban regions of Chengdu, Xi'an, Beijing, and
Tianjin were 62.6, 63.1, 27.0, and 14.6 times those in rural regions in
2018. This situation was common in China. Hence, China set up 13 prevention and
control regions (3 key regions and 10 city clusters, referred to as 3-10R) in 2013 to
improve air quality, and these areas were relatively developed regions
(
Differences in OC (top two rows) and ACS
Barbecue and cooking contributed a significant portion of OC emissions from the
FMSs, which led to a distinctive feature of emissions from the FMSs: there was a
certain correlation between OC emissions and local economic development. We
gathered disposable income per capita data from 2000 to 2018 for each
city, and the relationship between the disposable income and OC emissions per
capita has been assessed. As shown in Fig. 9, like other emission sources,
OC emissions from the FMSs and disposable income showed an inverted U-shaped
relationship (
The relationship between the per capita disposable income and OC
emissions from FMSs in China for the years from 2000 to 2018. Panel
In contrast to the relatively developed 3-10R, there are some contiguous
poor regions (CPRs) in China, located in the borderland or mountains
(
To combat air pollution, China introduced its toughest air pollution control
plan (APPCP) ever in 2013
(Q. Zhang
et al., 2019). The implementation of the APPCP has led to significant
improvements in China's air quality. Measures to control the FMSs have also
begun to be widely promoted (Fig. S14). A total of 76.3 % and 66.5 %
of cities had introduced policies to restrict emissions from the
catering industry and fireworks, respectively, before 2018. The pollutant removal
efficiencies of small, medium, and large catering businesses
are higher than 60 %, 75 %, and 85 %, respectively (national standard GB 18483-2001). Local
governments have the right to designate areas in which fireworks are
forbidden: these are usually urban areas as well as hospitals, factories, power
plants, schools, and transportation hubs
(
The impact of policies on the reduction of CA emissions. The
solid lines (left
If we assume that there is also a quadratic fitting relationship between the rural per capita OC emissions and income, the rural per capita OC emissions would start to decline when the rural per capita income reaches CNY 16 800. The control of CA emissions from the FMSs, such as cooking, should start from the perspective of increasing the income of rural residents. With sufficient income, residents will tend toward a more environmentally friendly and green lifestyle. In this case, a green lifestyle is embodied by the installation of a range hood. In 2017, the impervious surfaces of urban regions only accounted for 1.52 % of the national area (Gong et al., 2019), and rural regions were vast by contrast. Thus, the cost of controlling firework, sacrificial incense, and joss paper burning activity in rural regions will be much higher than in urban regions. For these sources, policies and standards should be set to limit their emissions. In addition, it is questionable whether the environmentally friendly fireworks currently on the market have a lower impact on the environment (Fan et al., 2021). Thus, manufacturers should be guided toward the development of environmentally friendly fireworks, joss paper, and sacrificial incense in order to reduce emissions.
Most of the relevant existing studies on emissions have
focused on the EFs of PM
(Jetter
et al., 2002; Lee and Wang, 2004; G. Wang et al., 2015; Kuo et al., 2016;
Jilla and Kura, 2017; Amouei Torkmahalleh et al., 2018; L. Wang et al., 2018;
Zhao et al., 2018; Lin et al., 2019), PAHs
(Yang
et al., 2005, 2013; Zhao et al., 2019), and volatile organic compounds (VOCs)
(Cheng
et al., 2016; L. Wang et al., 2018). Several metallic elements
(Croteau
et al., 2010; Shen et al., 2017) and organic matter components
(Xiang
et al., 2017; Que et al., 2019) have also been tested. However, few studies have
tested the OC and EC EFs of the FMSs
(See
and Balasubramanian, 2011; S. Zhang et al., 2019; Lin et al., 2021). Fireworks are the least-studied emission source, although they can emit
large amounts of particles. EFs of PM
Several studies have calculated the emission amount of the catering industry
(Table S5). For example, H. Wang et al. (2018)
calculated the VOC emissions (66 245 t) from restaurants in China based on
samples taken from nine types of restaurants. Jin et al. (2021)
calculated the OC emissions from the catering industry in China by undertaking investigations
in two cities in the Shandong and Shanxi provinces. The results showed that OC
emissions from the catering industry were 26.8 Gg, which was 66.0 times
the values obtained in this work. The EFs used in Jin et al. (2021) were the
generation rates of pollutants, which were 0.48 mg m
Previous research has calculated the total OC and BC emissions in China, such as the widely used the Multi-resolution Emission Inventory for China (MEIC) (OC: 2080–3190 Gg; BC: 1253–1728 Gg) and the Peking University (PKU) (OC: 2345–3587 Gg; BC: 1455–1624 Gg) emission inventories (R. Wang et al., 2014; Huang et al., 2015; Li et al., 2017). Residential sources or residential and commercial sources contributed most of the OC (80.3 % in MEIC and 71.4 % in PKU) and BC (51.5 % in MEIC and 51.0 % in PKU) emissions (Peng et al., 2019). The OC and BC emissions from the FMSs accounted for only 1.5 ‰–2.2 ‰ and 0.16 ‰–0.20 ‰ of their national total emissions. Thus, the OC and BC emissions from the FMSs were generally meager. During key periods, like the CNE, the contributions of the FMSs to the total OC and BC emissions can rise to 2.3 %–3.5 % and 1.1 %–1.6 %, respectively. In key areas, the contribution rates would be relatively higher. For instance, during the 2014 CNE, the FMSs contributed 6.3 % of the OC emissions in the Sichuan Basin and 2.9 % of the BC emissions in the Jiangxi–Hunan area. However, it should be noted that the fireworks were always set off from about 20:00 to 00:00 LT (local time) during the CNE; thus, intense emission amounts could be expected during this period. Therefore, the contribution of fireworks to CAs in the atmosphere during the CNE and CSF is still a topic of debate.
Widespread controversy has also stemmed from the fact that the government chooses not to control emissions from industry and vehicles during CNE but emphasizes controls on the emissions from fireworks. The public can not accept or believe that the emissions from fireworks can lead to serious air pollution, which could be a key reason why they can not be completely eradicated in cities. From this study, it can be seen that CA emissions are limited compared with those from residential sources. An interesting question that atmospheric scientists needed answer in the future is “If fireworks were not controlled, how many air pollutants from other major urban sources should be alternatively controlled in cities?”.
The dataset generated in this work is available at
The absence of anthropogenic sources in the existing inventories prevents
people from drawing accurate conclusions about the control of short-term
pollution. To calculate the emissions from these sources, which are difficult
to estimate, we construct an emission inventory establishment framework,
including a series of equations and methods. We use multiple proxy data,
such as questionnaire data, various statistical data, and points of interest data, to
build a dataset of the activity of the five missing sources (FMSs, including
cooking, fireworks, sacrificial incense and joss paper burning,
and barbecue). The carbonaceous aerosol (CA) emission factors were tested
in our lab using a custom-made sampling platform. The OC, EC, and BC EFs
were 5.86–203, 0.003–12.4m and 1.07–191 mg kg
The supplement related to this article is available online at:
YC was responsible for carrying out the experiments, processing the data, and writing the manuscript. SK conceptualized the study, developed the methodology, supervised the study, and reviewed and edited the manuscript. LY and HZ participated in the experiments, and LY, HZ, and JW undertook the formal analysis. QY, SZ, and ZN participated in experiments. YH was responsible for validation of the results. YY, ZS, GS, DL, SW, and SQ supervised the study.
The contact author has declared that none of the authors has any competing interests.
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This study was supported by the National Natural Science Foundation of China (grant nos. 42077202 and 41830965) and the Key Program of the Ministry of Science and Technology of the People's Republic of China (grant nos. 2016YFA0602002 and 2017YFC0212602).
This paper was edited by Bo Zheng and reviewed by two anonymous referees.