Contributions of China’s Wood-Based Panels to CO₂ Emission and Removal Implied by the Energy Consumption Standards

Abstract

Life cycle analysis on wood-based panels in terms of CO₂ flux can be used to quantitatively assess the climate change contributions of these materials. In this study, the annual CO₂ flux between 1990 and 2015 was calculated through gate-to-gate life cycle analysis of wood-based panels. As implied by the energy consumption standards, China’s wood-based panels used to be carbon sources during the period 1990–2007, with the average contribution to CO₂ emissions of 9.20 Mt/year. The implementation of new standards and the development of Cleaner production technologies in China, decreased the energy consumption per panel. China’s wood-based panels acted as a carbon sink between 2008 and 2015, with the average contribution to CO₂ removal of 31.71 Mt/year. Plywood produced the largest contributions to the emission and removal of CO₂, and was followed by fiberboard and particleboard. China’s wood-based panels, with good prospects and strong demands projected in the future, can potentially contribute to climate change mitigation.

1. Introduction

The ongoing international concern for climate change has obtained increased attention from developing countries due to their rapidly growing greenhouse gas (GHG) emissions [1]. China has committed to a 40%–45% reduction in GHG emissions per unit of gross domestic product (GDP) by 2020 compared with 2005 and has planned to peak in carbon emission reduction by around 2030 [2]. The growing concern over the impacts of climate change has emphasized the mitigation potential of forests and forest-derived products, specifically in terms of carbon sequestration [3]. The use of wood and wood-based products exerts positive effects on the environment, such as mitigating climate change or reducing waste and other emissions [4].

The wood-based panel industry is an important forest-based one in China. The country is the largest wood-based panel producer worldwide, with a total output of 286.80 million m³ in 2015 [5]. The main panels, namely, plywood, fiberboard, and particleboard account for 87.85% of China’s wood-based panel industry. Among wood-based panels, plywood dominates with 57.69% of production and is followed by fiberboard at 23.08% of the total output. The yield of particleboard accounts for 7.08% of the total output [5]. Due to the high economic importance of wood-based panels in China, the production has expanded considerably in recent years and is expected to increase with an average annual growth rate of 1.05% from 2015 to 2030 [6]. On the one hand, the carbon storage in wood-based panels has increased annually due to an increase in net primary production [7,8]. On the other hand, gate-to-gate product manufacturing consumes various energy sources, and almost all energy consumption results in GHG emissions [9].

The major GHG is CO₂ with less contribution from CH₄ and N₂O [10]. The contributions of wood-based panels include the contributions to annual CO₂ emissions and removals [11]. Direct emission occurs during production, whereas indirect emission is associated with purchased electricity and product end-of-life. Other emission types are associated with fiber and non-fiber productions, transportation, and product use [12]. In compensating for CO₂ emissions, the net removal contributions are obtained on the basis of the estimation of CO₂ stocks [13].

Several studies have focused on environmental impact assessments on wood-based panels. These studies compared the environmental influence of plywood, fiberboard, and particleboard to address issues of global warming, acidification, eutrophication, dust, wastes, and resource consumption [14]. Syahirah [15] compared the environmental impacts of panel preparation, shaping, and finishing on the wood-based industry in Malaysia. The growing focus on carbon as an indicator of environmental performance [16] has encouraged studies on carbon flux through the processing stages, carbon stored in products, and carbon footprint for on-site manufacture and cradle-to-product gate processes. Wilson [10,17] and Sakimoto [18] calculated the carbon footprints of production of American particleboard, medium-density fiberboard, and softwood plywood, using the Simapro 7.1 software (Pre’Consultants, Amersfoort, The Netherlands) and assessed the CO₂ fluxes of these materials through the carbon content in the products. Garcia and Freire [19] compared three different tools for assessing environmental impact of particleboard and showed that treating biogenic CO₂ causes the main difference in global warming and greatly benefits global warming. In 2012, Bergman et al. [20] quantified environmental impact using the life cycle assessment method on five wood-based panel products made in North America.

The literature review shows that stored carbon per unit of wood-based panels can offset the carbon emissions from on-site manufacturing and is better than climate-neutral materials with a carbon store equal to their carbon emissions. Some studies have only estimated carbon storage of the national wood-based panel pool and its mitigation potential [21,22]. Few studies have comprehensively assessed the contributions of national wood-based panels to CO₂ emissions or removals. Less attention has been attached to GHG contributions to the atmosphere. Current research in China is restricted to carbon footprint or carbon stock calculations per volume of fiberboard and particleboard [23,24].

The climate change contributions should be assessed and the environmental profile of wood-based panels should be improved in China to meet its GHG emission reduction targets. This work focused on the environmental impact of CO₂ emission or removal. CO₂ flux can be used to comprehensively assess the actual effects of products on climate change within their entire life cycle [25]. This work derived the annual CO₂ fluxes through the life cycle of wood-based panels to determine their role in climate change between 1990 and 2015.

2. Methodology and Data

2.1. System Dynamic Structure and Functional Unit

The first step in calculating CO₂ flux is to determine the system boundary of wood-based carbon flow, which uses two major system boundaries [26]. One is the cradle-to-grave system boundary, which consists of five phases, namely, raw material extraction, product production, packaging and transportation, product use, and waste disposal [27]. As illustrated by the flow diagram in Figure 1, the cradle-to-grave analysis applied in the life cycle of harvested wood product (HWP) assesses various environmental impacts over the entire product life cycle, from raw material extraction (the cradle), via production, transportation and use, to waste management (the grave) [28]. Wood-based carbon stocks are divided into many sub-fluxes passing through various pools and processes before being released into the atmosphere [29]. The other is the gate-to-gate system boundary, which consists of two phases, namely, product manufacture and use [20,30].

For our analysis, the gate-to-gate system boundary was used (Figure 2). Forest trimmings and industrial waste wood from sawmills, such as shavings, sawdust, ply trim, veneer, and chips, are sources of raw wood materials. Plywood mostly uses large-diameter timbers as raw materials. Fiberboard and particleboard mostly use small-diameter timbers and wood residues (i.e., harvesting, building, and processing residues) from sawmills and other wood industries as major raw materials. Moreover, bark from logs and sawdust may be used to produce wood-based panels [31].

Plywood production involves raw material preparation; peeling, drying, and veneer finishing; gluing and hot processing; sawing and sanding; and packaging. Carbon emission primarily occurs during gluing [32]. Fiberboard production includes raw material preparation, pulping, forming, hot processing, and after-treatment. Pulping and forming consume much energy during production [33]. Particleboard production comprises raw material preparation, particle preparation, particle drying, particle sizing, slab paving, hot pressing, and after-treatment. The energy is primarily consumed through particle preparation, drying, slab paving, and hot pressing, which account for 87.46% of the total energy consumption [34]. The three panels are produced by coordinating various procedures, which also produce pollutants and GHGs.

Using the atmospheric carbon flow as the evaluation objective, IPCC [35] stipulates that direct and indirect CO₂ emissions are positive GHG contributors and that carbon stock and substitution emission reduction are negative GHG contributors. The equation for CO₂ flux is given by:

$$CF=CE-CS$$

(1)

where $CF$, $CE$ and $CS$represent the values of CO₂ flux, CO₂ emission, and CO₂ stock, respectively. If the value is above zero, then the product is a net emitter. Otherwise, the product is a net sink. CO₂ emission reduction is stipulated as a negative value [36]. The capability of carbon sinking depends on the absolute value. A high absolute value indicates increased contribution to CO₂ removal from the atmosphere [25].

The functional unit describes the quantitative measure of the functions that a product or service provides [37]. In this study, the investigated products were wood-based panels. The 2013 Revised Supplementary Methods and Good Practice Guidance Arising from the Kyoto Protocol (The 2013 IPCC Guidelines) [11] stipulates that wood-based panels are reported in cubic meters (m³) solid volume, a functional unit used in previous wood-based panel studies [10,38,39]. Therefore, the volumetric unit (m³) was adopted as the reference in the current work to compare the gate-to-gate life cycle CO₂ flux among different panels.

2.2. CO₂ Emission and Energy Consumption Standard

This work calculated the CO₂ emissions from the production process in accordance with energy consumption standards. The overall energy consumption standards of wood-based panel production are China’s forestry industry standards issued by State Forestry Administration of the People’s Republic of China. These standards are recommended standards and define the relevant terms of on-site manufacture of wood-based panels and the indexes of energy consumption for producing 1 m³ of panels. q₁ represents the specific value of the indexes and is given in kgce/m³. Through the investigation of typical wood-based panel enterprises in China, the energy consumption of different types of enterprises was obtained. Surveyed enterprises accounted for more than 20% of the entire industry, and more than 50% of the total output was investigated. The energy consumptions per unit production of enterprises with an annual production of 50,000 m³ of plywood and 0.2 million m³ of particleboard were taken as the basic values [40,41,42], on which the different levels of indexes were based. The index values of different grades can represent the actual energy consumption of Chinese wood-based panel enterprises. The amounts of energy consumption in the entire production system were summed up and converted into standard coal [32,33,34]. Energy consumptions are divided into three levels in accordance with the standards, and the specific meaning of each level is as follows.

The third and qualified grades represent the limit values of energy consumption per unit product and are mandatory indicators. The purpose of these grades is to eliminate the backward production capacity of 20%–30%. The second and good grades represent the threshold values of energy consumption per unit product and are mandatory indicators. They are admittance values for production of per unit value of energy consumption for new construction, reconstruction, and expansion of enterprises. The first and excellent grades represent the advanced values of energy consumption per unit product and are recommended indicators. The numerical values indicated by the indexes are in line with the international advanced levels or the leading domestic levels for production of wood-based panels and are the goals of enterprises for on-site manufacture. Energy consumption standards are the principles that enterprises should follow in producing wood-based panels. The enterprises should calculate the energy consumption of the actual production process and match them to the grade in the standards. The comprehensive energy consumption per unit output of an enterprise in actual production refers to the ratio of total energy consumption to qualified output in the same statistical period.

Table 1. Indexes of energy consumption for producing 1 m³ of panels in the first stage (kgce/m³).

Wood-Based Panels	Indexes	Areas
		Southern Provinces	Northern Provinces
Plywood	First grade	320 < q1 ≤ 450	420 < q1 ≤ 600
	Second grade	450 < q1 ≤ 600	600 < q1 ≤ 830
	Third grade	600 < q1 ≤ 900	830 < q1 ≤ 1100
Fiberboard	First grade	q1 ≤ 700	q1 ≤ 750
	Second grade	700 < q1 ≤ 750	751 < q1 ≤ 850
Particleboard	First grade	20 < q1 ≤ 410	260 < q1 ≤ 490
	Second grade	410 < q1 ≤ 590	490 < q1 ≤ 670
	Third grade	590 < q1 ≤ 830	670 < q1 ≤ 900

Note: the arrangement is based on three standards: LY/T 1529–1999, LY/T 1451–1999, and LY/T 1530–1999. q₁ represents the actual energy consumption for on-site manufacture of 1 m³ of wood-based panels.

and

Table 2. Indexes of energy consumption for producing 1 m³ of panels in the second stage (kgce/m³).

Wood-Based Panels	Indexes	Values
Plywood	Excellent	q1 ≤ 200
	Good	200 < q1 ≤ 240
	Qualified	240 < q1 ≤ 260
Fiberboard	Excellent	q1 ≤ 320
	Good	320 < q1 ≤ 380
	Qualified	380 < q1 ≤ 450
Particleboard	Excellent	q1 ≤ 120
	Good	120 < q1 ≤ 160
	Qualified	160 < q1 ≤ 200

Note: the arrangement is based on three standards: LY/T 1529–2012, LY/T 1451–2008, LY/T 1530–2011.

show the different indexes according to the energy consumption standards between 1990 and 2015. The different levels of indexes were used to judge the actual production level of wood-based panel industry and service as a reference for the government to supervise the consumption of energy for production. The quantitative management of resource consumption by the state may urge enterprises to examine the energy consumption in each production process in accordance with the energy consumption levels and to reduce waste of resources. The backward production capacity that fails to meet the third and qualified grades will be eliminated [43]. The implementation of the total energy consumption standards of the wood-based panel industry in China occurs in two stages. The first stage includes LY/T 1529–1999 Total Energy Consumption in Plywood Production (LY/T 1529–1999), LY/T 1451–1999 Comprehensive Energy Consumption for Hard Fiberboard Production on the Wet Process (LY/T 1451–1999), and LY/T 1530–1999 Total Energy Consumption in Particleboard Production (LY/T 1530–1999), which were released in 1989 and implemented in 1990 [32,33,34].

In the first stage, the four major producers of Chinese wood-based panels are Linyi, Shandong Province; Pizhou, Jiangsu Province; Jiashan, Zhejian Province; and Wen’an, Hebei Province. Among these producers, three are located in the northern provinces (The Technical Requirements of Cleaner Production for the Wood-based Panel Industry in China defines the southern and northern provinces as the area with heating facilities and the area without heating facilities, respectively.) (i.e., Linyi, Pizhou, and Wen’an), and the total output and market share of wood-based panels of Shandong, Jiangsu, and Hebei provinces account for more than 80% of the national share. This work selected the northern provinces as regional indicators.

In terms of first-level indexes, the average energy consumptions of plywood, fiberboard, and particleboard were 510, 750, and 375 kgce/m³, respectively (Table 1)

The second stage (2008–2015) includes three current national standards: LY/T 1529–2012 Comprehensive Energy Consumption of Plywood Production (LY/T 1529–2012), LY/T 1451–2008 Overall Energy Consumption for Fiberboard Production (LY/T 1451–2008), and LY/T 1530–2011 Comprehensive Energy Consumption of Particleboard Production (LY/T 1530–2011) [40,41,42]. Replacing the previous energy consumption standards with the current ones includes the implementation of Excellent, Good, and Qualified index levels. The north and south areas are also unified in the same index. The reduction in energy consumptions for wood-based panel production is attributed to the application of cleaner production technologies. China’s enterprises have been urged to adopt cleaner production technologies through the improvement of technologies and utilization of clean materials [44]. Thus, the calculations based on the “first grade” (Table 1) and “excellent grade” (Table 2) met the requirements for cleaner production in China’s wood-based panel industry. According to the statistics, the energy consumption of China’s advanced enterprises is 163–182 kgce/m³, and that of most small- and medium-scale enterprises is 250 kgce/m³ [45]. In addition, in the research of 20 representative enterprises, the energy consumption per unit of particleboard is 113.03 kgce/m³ [46]. The values of actual practice conform to the first-level indexes. The results of related foreign literature showed that the energy consumptions for plywood production in the United States and Canada are 158.46 and 80.15 kgce/m³ [47] and that the domestic practical conditions of China are close to advanced levels. Therefore, the index selection conforms to the current situation of the industry and the actual situation.

In the second stage, the average energy consumptions for on-site manufacturing of plywood, fiberboard, and particleboard in terms of excellent-grade indexes were 200, 320, and 120 kgce/m³, respectively.

2.3. CO₂ Stock and Calculation Model

2.3.1. IPCC Methodology

The 2006 IPCC Guidelines for National Greenhouse Gas Inventories (The 2006 IPCC Guidelines) identifies three feasible approaches to estimate and report national carbon stock changes of HWPs, namely, the stock change approach, the atmospheric flow approach, and the production approach. Following the 17th session of the Conference of the Parties, carbon accounting of HWP is confined to products in use, where the wood was derived from domestic harvest [48]. The principle is the same as the production approache (PA), a universal approach during the second commitment period of the Kyoto Protocol [49]. The current study calculated the gate-to-gate CO₂ flux in which the system boundary disregarded trade and excluded carbon in imported wood-based panels [11]. The PA was used to calculate only the carbon stock changes.

The first step is to estimate the share of domestically produced wood-based panels. Following the 2013 IPCC Guidelines, the domestic consumption of industrial roundwood was assumed equal to the feedstock used for manufacturing the wood-based panels. The fraction of industrial roundwood from domestic forests was computed on the basis of the production, import, and export of industrial roundwood in accordance with Equation (2):

$$f_{IRW}\left(i\right)=\frac{IR{W}_P\left(i\right)-IR{W}_{EX}\left(i\right)}{IR{W}_P\left(i\right)+IR{W}_{IM}\left(i\right)-IR{W}_{EX}\left(i\right)}$$

(2)

where $f_{IRW}\left(i\right)$ is the share of industrial roundwood used in the domestic wood-based panel production with respect to the total consumption of industrial roundwood in year$i$; $IR{W}_P\left(i\right)$,$IR{W}_{IM}\left(i\right)$ and $IR{W}_{EX}\left(i\right)$ represent the carbon content in the produced, imported, and exported industrial roundwood in year$i$, respectively.

The present work assumed that all domestic wood harvests were from sustainably managed forests; therefore, the calculation of carbon stocks did not differ among different afforestation activities. Equation (3) was used to calculate the annual fraction of wood-based panels entering the accounting framework from domestic harvest as follows:

$$\mathrm{HWP}\left(i\right)=\mathrm{P}\times f_{IRW}\left(i\right)$$

(3)

where$\mathrm{HWP}\left(i\right)$ is the number of wood-based panels produced from domestic harvest in year $\left(i\right)$, $\mathrm{P}$ is the total number of wood-based panels produced in year$i$.

The annual inflow and outflow for wood-based panels were estimated by applying default conversion factors and a first-order decay function, with the constant annual default decay factors proposed by the 2013 IPCC Guidelines. Changes in carbon stocks in year$i$ were estimated in accordance with the following equations:

$$C\left(i+1\right)=e^{-k}\times C\left(i\right)+\left[\frac{\left(1-e^{-k}\right)}{k}\right]\times inflow\left(i\right)$$

(4)

$$\mathsf{\Delta }C\left(i\right)=C\left(i+1\right)-C\left(i\right)$$

(5)

where $C\left(i\right)$ is the carbon stock of wood-based panels at the beginning of year$i$;$C\left(1900\right)=0$; $k$ is the first-order decay rate equal to$\frac{\ln \left(2\right)}{HL}$, where $HL$ is the half-life of the wood-based panels; $inflow\left(i\right)$ is the inflow of wood-based panels to the carbon pool in year$i$;$\mathsf{\Delta }C\left(i\right)$ is the carbon stock change of each wood-based panel during year$i$.

2.3.2. Selection of Parameters and Data Sources

The basic density of the wood-based panels in this work was adopted from the national standard GB/T 1933–2009, the Method for Determination of the Density of Wood. The moisture content was adopted from the national standard GB/T 1931–2009, the Method for Determination of the Moisture Content of Wood. The carbon fraction was adopted from the published literature data in China [50]. The half-life values and first-order decay rate were based on the default data provided by the 2013 IPCC Guidelines.

Table 3. Various carbon conversion factors of wood-based panels.

Wood-Based Panels	Density (t/m3)	Carbon Fraction (%)	Carbon Factor (tc/m3)	Moisture Content (%)	Half-Life (years)	Decay Rate (K)
Plywood	0.520	0.443	0.230	6	25	0.028
Fiberboard	0.760	0.465	0.353	4	25	0.028
Particleboard	0.620	0.470	0.291	5	25	0.028

Note: various carbon conversion factors of wood-based panels in China are adopted from published studies [11,50].

shows the conversion parameters used in the calculation of carbon stocks in wood-based panels. The carbon stock changes were converted to CO₂ by 3.67 [10].

The data of the total production, import, and export of industrial roundwood and total production of wood-based panels between 1990 and 2015 were from the China Forestry Statistical Yearbook. The stock of wood-based panel carbon pool was cumulative. Calculating the carbon stock required values from the previous year. The 2006 IPCC Guidelines recommends that calculation of the carbon stock of HWP starts from 1900 and assumes that the value prior to 1900 is zero [35]. The current production of industrial roundwood and wood-based panels, as well as the trade data recorded in the China Forestry Statistical Yearbook can be traced back to 1949. Data prior to 1949 can be reverse-calculated using 1949 data as a benchmark in Equation (6) [51].

$$V_i=V_i^{\prime }\times e^{\left(u\times \left(i-i^{\prime }\right)\right)}$$

(6)

where $u$ is the continuous rate of change in industrial roundwood consumption for China at default data of 0.0217; $V_i$is the annual production, import, or export of industrial roundwood and various wood-based panels in year$i$ tracing back to 1900;$V_i^{\prime }$ is the annual production, import, or export of industrial roundwood and various wood-based panels in the benchmark year; $i$is the year;$i^{\prime }$ is the benchmark year.

3. Results

3.1. CO₂ Emissions

The annual CO₂ emissions in the production of the wood-based panel industry were derived and are shown in Figure 3.

The numbers of standard coal were converted to CO₂ with a conversion coefficient of 2.54 t CO₂/tce [52]. On-site CO₂ emissions for manufacturing plywood, fiberboard, and particleboard were 1.30, 1.91, and 0.95 t CO₂/m³, respectively, during the period 1990–2007. From the production and trade data in the China Forestry Statistical Yearbook, the average annual CO₂ emitted to the atmosphere was found to be 7.80 Mt in the first stage.

In the second stage, China’s wood-based panel industry experienced a new round of rapid growth, with an average annual yield of 171.96 million m³. On-site manufacturing of 1 m³ of plywood, fiberboard, and particleboard produced 0.51, 0.81, and 0.30 t CO₂, respectively. The average annual CO₂ emitted to the atmosphere was 21.84 Mt CO₂, which is 1.8 times of the first stage, due to the rapid growth of yields and low energy consumptions.

Total CO₂ emission was found to grow in each stage. The annual CO₂ emissions of plywood manufacturing were the highest at approximately 17.58 Mt/year and were followed by those of fiberboard (15.78 Mt/year). Particleboard had the lowest annual CO₂ emission contributions due to the low yields and CO₂ emission per unit.

3.2. CO₂ Stock Changes

Forests sequester atmospheric CO₂ to produce wood, and carbon stored in wood products is emitted as CO₂ and CH₄ when burned [53]. As shown in Figure 4, China’s annual CO₂ stock changes of wood-based panels continuously increased from 1990 to 2015. Using established national data and the PA to carbon storage, the net increase in CO₂ stored in 1990 was calculated to be 1.88 Mt whereas it was calculated to be 125.49 Mt in 2015. The annual average increments of plywood, fiberboard, and particleboard were 19.06, 15.70, and 4.98 Mt CO₂, respectively. Plywood had the highest annual output and thus had the most significant changes in CO₂ pool.

The carbon stock of China’s HWP products rapidly increased after 2003 mainly due to the rapid development of China’s forestry that gained an important position in the sustainable development of China’s national economy. After 2001, the production of China’s wood-based panels increased at a rapid speed, thereby increasing the annual stock.

3.3. Annual CO₂ Fluxes and Contributions

Figure 5 exhibits the gate-to-product gate CO₂ fluxes of wood-based panels between 1990 and 2015.

Wood-based panel contributions varied from approximately 1.54 Mt CO₂ to 27.74 Mt CO₂/year between 1990 and 2007. The largest emitter was plywood (i.e., 4.61 Mt CO₂/year), followed by fiberboard (i.e., 4.37 Mt CO₂/year) and particleboard (i.e., 0.22 Mt CO₂ CO₂/year). In this stage, wood-based panels were carbon sources and CO₂ emissions of on-site manufacture exceeded the CO₂ stored in the products. The annual CO₂ emission contributions to the atmosphere were 9.20 Mt. With the increase in outputs, China’s wood-based panels produced large amounts of CO₂ to the atmosphere.

The implementation of new standards led to the decrease in energy consumption per panel in the second stage. On the contrary, an increasing trend of the production of wood-based panels with an annual growth rate of approximately 25% was observed. In 2008–2015, wood-based panels acted as a carbon sink. CO₂ storage in wood products offset the manufactured CO₂ released to the atmosphere [20]. The average annual CO₂ removal contributions were 31.71 Mt/year, with the contributions of plywood, fiberboard, and particleboard at 15.17, 9.59, and 6.95 Mt CO₂/year, respectively. Considering the same trend with the first stage, plywood played the most important role in removing CO₂. The greater the output, the greater the contributions to CO₂ removal.

The CO₂ contributions between the two stages were the exact opposite. The difference between CO₂ storage and emissions varied from positive to negative; therefore, the wood-based panel pool in China changed from a carbon source to a carbon sink. This finding was mainly due to the fact that energy consumption per panel for on-site manufacture decreased and panel production significantly increased.

4. Discussion

4.1. Methodological and Data Constraints

The underlying assumptions presented in this work can be improved through in-depth analyses such as (1) considering the substitution of emission reduction to decrease the life cycle of GHG emissions, (2) studying the climate change mitigation potential of wood-based panels through the cradle-to-grave system boundary, and (3) achieving acute and specific data and methods. Some methodological and data constraints are discussed below.

Analysis based on default data and methods presents a methodological weakness, because of the absence of available data. The accuracy and quality of results in this work depended on the data and method quality. Using the default data and methods provided by IPCC and previous publications introduced uncertainties. This work calculated the CO₂ stock changes based on the default half-lives that were distinguished among main wood-based panels. A total of 25 years were used as half-lives in the current work whereas some studies estimated them to be shorter than 25 years [50,51]. This work might have overestimated the CO₂ stock changes.

The 2013 IPCC Guidelines describes three methods based on the level of detail and accuracy of the available data: (1) instantaneous oxidation (Tier 1), (2) first-order decay (Tier 2), and (3) country-specific methods (Tier 3). The country-specific method can be used if a large number of detailed data and methodologies are available. Under the Tier 3 method, accurate country-specific information is applied to improve the accuracy of the estimates. If consistent, transparent, and verifiable parameters (i.e., service life information and conversation factors of products) are applied to country-specific methods, then the estimates of carbon removal contributions can increase in accuracy and reliability.

The current national environmental standard for the wood-based panel industry stipulates that imported wooden raw materials should come from sustainable forests and that national wooden raw materials should comply with the forestry laws and regulations in China [54]. The carbon in wood-based panels is allocated to particular forest activities because different estimates of contributions depend on the wood origin. The harvest from deforestation is regarded as instantaneous oxidation. This work disregarded deforestation activities because of the lack of data. Thus, the CO₂ contributions were overestimated. Forest activities should be differentiated in the future.

4.2. Potential of China’s Wood-Based Panels in Reducing CO₂ Emissions of On-Site Manufacture

The wood-processing industry standard in China has a low requirement in energy consumption indexes [55]. The energy consumption per unit output of China’s wood-based panel is 4.8 times that of the world [56]. As presented in

Table 4. CO₂ fluxes through the gate-to-gate life cycle of wood-based panels in China and the United States (t/m³).

Countries		Wood-Based Panels		CO2 Emissions	CO2 Stocks	CO2 Fluxes
China	First stage	Plywood		1.30	0.85	0.45
		Fiberboard		1.91	1.30	0.61
		Particleboard		0.95	1.07	−0.12
	Second stage	Plywood		0.51	0.85	−0.34
		Fiberboard		0.81	1.30	−0.49
		Particleboard		0.30	1.07	−0.77
USA		Plywood	PNW	0.13	0.84	−0.71
			SE	0.20	0.98	−0.78
		Fiberboard		0.08	1.27	−1.19
		Particleboard		0.18	1.05	−0.87

Note: CO₂ emissions and stocks of wood-based panels in the United States are adopted from Consortium for Research on Renewable Industrial Materials Report [57]. The carbon calculation of plywood is divided into two types on the basis of region: PNW (Pacific Northwest) and SE (Southeast).

, CO₂ emissions during the wood-based panel production were higher in China than those in the United States. The gate-to-gate life cycle CO₂ fluxes of China’s wood-based panels were lower than those of the United States. China’s wood-based panel industry has a high CO₂ emission reduction potential in on-site manufacture.

However, the decrease in energy consumption indexes for wood-based panel production indicates that China’s wood-based panels can potentially reduce CO₂ emissions of on-site manufacture. China is committed to reducing or avoiding pollutant emissions during production, service, and use. The implementation of cleaner production technologies reduces or eliminates pollution from the environment by improving the technologies and using clean materials. For more than 10 years, the index values of total energy consumption standards have declined. The reduction in energy consumption during production shows that China’s wood-based panels present strong GHG reduction capacity and energy-saving potential.

4.3. Ways to Enhance CO₂ Removal Contributions of China’s Wood-Based Panels

Climate change can be mitigated through the use of wood products that reduce carbon emissions and remove carbon [58,59]. Global carbon emissions can be mitigated using two methods: (1) directly reducing carbon emissions and (2) indirectly increasing carbon storage [60].

Cleaner production technologies must be carried out to reduce energy and resource consumption in production and thus reduce CO₂ emissions [14]. Energy consumption occupies a large proportion in the cost of wood-based panel products; the energy costs of plywood, fiberboard, and particleboard are 25%, 30%, and 30%, respectively [46,61,62].

Carbon mitigation or slowing carbon emissions over time can also be achieved using various CO₂ stock approaches, such as extending the life span of HWP, recycling and reusing disposed HWPs, and improving the production efficiency of HWPs. These approaches cannot directly mitigate carbon emissions or indirectly increase carbon storage. However, they can provide a significant time lag between carbon sequestration from the atmosphere and carbon emissions back into the atmosphere [60].

4.4. Nature of Cleaner Production Technologies in China’s Wood-Based Panel Industry

Cleaner production is based on holistic and preventative approaches; if this technology is implemented society-wide, then societies can be sustainable [63]. Cleaner production has been adopted by China as a primary tool to fight against industrial pollution [64]. During the 12th Five-Year Plan (2011–2015), the energy consumption per unit of GDP fell by approximately 16% compared with the 1.03 tce in 2010 [65]. To achieve national emission reduction targets, cleaner production technologies have been applied in China’s wood-based panel industry. The values in

Table 5. Indexes of cleaner production technologies for wood-based panel production in China (kgce/m³).

Wood-Based Panels	Indexes	Values
Fiberboard	First grade	q1 ≤ 200
	Second grade	q1 ≤ 390
	Third grade	q1 ≤ 440
Particleboard	First grade	q1 ≤ 120
	Second grade	q1 ≤ 150
	Third grade	q1 ≤ 200

Note: the arrangement is based on two standards: Cleaner Production Standard-Wood-Based panel Industry (Medium-density Fiberboard) and Cleaner Production Standard-Wood-Based panel Industry (Particleboard).

show the grades for cleaner production technologies in wood-based panel production.

The first grade represents the advanced level of international cleaner production, the second grade represents the advanced level of cleaner production in China, and the third grade represents the basic level of cleaner production in China.

China’s energy consumption standards for wood-based panels have been revised in recent years (Table 1 and Table 2) and energy consumptions for production of 1 m³ of wood-based panels have decreased. These amendments conform to the requirements of cleaner production t in China.

Another reason for the decrease in energy consumption for production of 1 m³ of wood-based panels was the large increase in output. The comprehensive energy consumption per unit output of an enterprise in actual production refers to the ratio of total energy consumption to qualified output in the same statistical period. Clean production technologies reduce the total energy consumptions for on-site manufacture. An increase in output means low energy consumption per unit of product.

5. Conclusions

China is one of the major countries that aim to reduce GHG emissions. As a pillar of the forestry industry, the production and use of wood-based panels in China have a significant impact on the contribution of GHGs. Assessing the life cycle of CO₂ fluxes revealed the role of China’s wood-based panel industry in mitigating climate change and quantifying CO₂ emission and removal contributions in different panels. For our analysis, we estimated CO₂ emissions through product production and CO₂ stored during their useful lives. The results showed that China’s wood-based panels were carbon sources between 1990 and 2007. As implied by the energy consumption standards for wood-based panel production, energy consumption per panel for on-site manufacture decreased. Panel production in China also increased considerably. The two factors had made China’s wood-based panels a carbon sink in 2008–2015. Between the two stages, plywood produced the largest contributions whereas particleboard provided the smallest contributions. The changes in annual CO₂ fluxes showed that the use of wood-based panels met the GHG emission targets in China. Therefore, cleaner production technologies must be carried out to reduce energy consumption and GHG emissions in panel production. China’s wood-based panels, with good prospects and strong demands projected in the future, can potentially contribute to climate change mitigation.