3.1 Model building
According to the relevant research, environmental regulation policies can be divided into three types: command-control type, market incentive type, and information disclosure type (Li and Shen 2008). In this study, we mainly focus on the control of total carbon emissions (\(T\)) under the carbon emission trading mechanism, which is a command-control type and market incentive type. Usually, the government’s choice of \(T\) is not the result of considering social welfare, but the result of weighing economic growth and environmental protection. Under the goal of green development, government departments are formulating the total carbon emission control target \(T\). But whether the choice of \(T\) improves social welfare is still unknown. In other words, it is difficult to consider multiple regulatory objectives by only adjusting one exogenous regulatory variable \(T\). To solve this problem, carbon tax is levied on the enterprises’ actual emission under the condition of total carbon emission control. The tax rate is \(\tau ,\tau \ge 0.\)
Assume that the trading price of emission rights is\(\theta , \theta \ge 0\). \(r\) is affected by the total amount of carbon emissions \(T\), the carbon tax rate \(\tau\), and the supply and demand relationship in the carbon emissions trading market. Let the initial emission quota of enterprise \(i\) be \({t}_{i}\). The enterprise \(i\) can use emission rights for production or sell them with a quantity of \({q}_{i}({q}_{i}\le {t}_{i})\) in the emission rights trading market
$$\underset{{y}_{i},{r}_{i},{q}_{i}}{\text{max}}{\pi }_{i}\left({y}_{i},{r}_{i},{q}_{i}|{Y}_{-i},\theta \right)={y}_{i}{p}_{i}\left({y}_{i};{Y}_{-i}\right)+\theta {q}_{i}-{c}_{i}k{q}_{i}{r}_{i}^{2}-\tau k{y}_{i}\left(1-{r}_{i}\right)$$
1
s.t. \(k{y}_{i}\left(1-{r}_{i}\right)\le {t}_{i}-{q}_{i}\)
where the decision variables include the output \({y}_{i}\), the emission reduction ratio \({r}_{i}\) and the emission trading volume \({q}_{i}\). \({p}_{i}\left({y}_{i};{Y}_{-i}\right)\) is the product price of the enterprise \(i\). \(Y\) represents the total output of the industry, and \({Y}_{-i}\) represents other enterprises’ output except the enterprise \(i\). \(k\) is the industry pollution coefficient, and satisfies \(k>0\), which represents the emission by producing per unit of output without emission reduction. The total emission of producing \({y}_{i}\) output is \(k{y}_{i}\). At the same time, the emissions’ share \({r}_{i}\) of the enterprise \(i\) can be reduced by improving equipment, upgrading technology, etc, \(0\le {r}_{i}\le 1\). The enterprise \(i\) chooses the optimal \({r}_{i}\) according to its own profit maximization problem. The actual emission is \(k{y}_{i}\left(1-{r}_{i}\right)\), and the carbon tax paid is \(\tau k{y}_{i}\left(1-{r}_{i}\right)\). Emission reduction needs to pay a certain cost. For the same enterprise, it is difficult to achieve high emission reduction. High emission reduction would result in higher unit emission reduction costs (Levi and Nault, 2004; Subramanian et al., 2007). Therefore, we set the total emission reduction cost as \({c}_{i}k{y}_{i}{r}_{i}^{2}\), \({c}_{i}>0\).
According to the total emission reduction cost setting, the unit emission reduction cost of an enterprise is mainly related to the proportion of enterprise’s emission reduction. Here the unit emission reduction cost is \({c}_{i}{y}_{i}\).
To reflect the mutual competition between enterprises in the same market, the mutual impact of enterprise decision-making behavior must be considered. According to the conventional thinking of industrial organization research, we set the following price function:
$${p}_{i}\left({y}_{i};{Y}_{-i}\right)=\alpha -\beta {y}_{i}-\delta \beta {Y}_{-i}$$
2
where \(0<\delta <1\) indicates the degree of product differentiation. \(\delta\) represents the degree of homogeneity and differentiation. Both \(\alpha\) and \(\beta\) are known parameters greater than zero.
Based on the complementary relaxation properties, the constraint condition needs to be a tight constraint to obtain the maximum value of the formula (1). So, we have \(e{q}_{i}\left(1-{x}_{i}\right)={s}_{i}-{t}_{i}\). Combining the formula (2) and the tight constraint, the formula (1) can be simplified as follows:
$$\underset{{y}_{i},{r}_{i}}{\text{max}}{\pi }_{i}\left({y}_{i},{r}_{i}|{Y}_{-i},\theta \right)={y}_{i}\left(\alpha -\beta {y}_{i}-\delta \beta {Y}_{-i}\right)+\theta {t}_{i}+k{y}_{i}\left[-{c}_{i}{r}_{i}^{2}+\left(\theta +\tau \right){r}_{i}-\left(\theta +\tau \right)\right]$$
3
s.t. \(0\le {r}_{i}\le 1\)
3.2 Market equilibrium
In the formula (3), \({y}_{i}\) and \({r}_{i}\) are decision variables, where \({r}_{i}\) is only related to the part “\(-{c}_{i}{r}_{i}^{2}+\left(\theta +\tau \right){r}_{i}-\left(\theta +\tau \right)\)”. To obtain the maximum value of the formula (3), \({r}_{i}=\frac{\theta +\tau }{2{c}_{i}}\) is required. When \(0\le \theta +\tau \le 2{c}_{i}\), we have \(0\le {r}_{i}\le 1\), \({r}_{i}\) corresponds to the internal solution. When \(\theta +\tau >2{c}_{i}\), \({r}_{i}=1\), the formula (3) has a corner solution. Therefore, the following two situations are discussed:
①When \(0\le \theta +\tau \le 2{c}_{i}\), the solution of the formula (3) satisfies \({r}_{i}=\frac{\theta +\tau }{2{c}_{i}}\). Substituting \({r}_{i}\) back to the formula (3), then the maximization problem corresponds to the Lagrange equation is:
$${\mathcal{L}}_{i}={y}_{i}\left(\alpha -\beta {y}_{i}-\delta \beta {Y}_{-i}\right)+\theta {t}_{i}-k{y}_{i}\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{i}}\right)$$
4
First-order condition:
$$\frac{\partial {\mathcal{L}}_{i}}{\partial {y}_{i}}=\alpha -2\beta {y}_{i}-\delta \beta {Y}_{-i}-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{i}}\right)=0$$
5
From the formula (5):
$${y}_{i}=\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{i}}\right)}{\left(2-\delta \right)\beta }$$
6
②When \(\theta +\tau >2{c}_{i}\), \({r}_{i}=1\). From \({q}_{i}={t}_{i}-k{y}_{i}\left(1-{r}_{i}\right)\), \({q}_{i}={t}_{i}\). Substituting it back into the formula (3), the Lagrange equation corresponding to the maximization problem is:
$${\mathcal{L}}_{i}={y}_{i}\left(\alpha -\beta {y}_{i}-\delta \beta {Y}_{-i}\right)+\theta {t}_{i}-k{c}_{i}{y}_{i}$$
7
First-order condition:
$$\frac{\partial {\mathcal{L}}_{i}}{\partial {y}_{i}}=\alpha -2\beta {y}_{i}-\delta \beta {Y}_{-i}-k{c}_{i}=0$$
8
From the formula (8):
$${y}_{i}=\frac{\alpha -\delta \beta Y-{kc}_{i}}{\left(2-\delta \right)\beta }$$
9
Notice that the second-order condition \(\frac{{\partial }^{2}{\mathcal{L}}_{i}}{\partial {y}_{i}^{2}}=-2\beta <0(\beta >0)\) always satisfy for the internal solution (\(0\le \theta +\tau \le 2{c}_{i}\)) and the corner solution (\(\theta +\tau >2{c}_{i}\)). So, the second-order condition of the formula (3) always holds. Therefore, according to the above analysis, we can know that there are two solutions to the profit maximization problem of the enterprise \(i\), which are:
①When \(0\le \theta +\tau \le 2{c}_{i}\), there is an internal solution.
$${y}_{i}=\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{i}}\right)}{\left(2-\delta \right)\beta }, {r}_{i}=\frac{\theta +\tau }{2{c}_{i}}, {q}_{i}={t}_{i}-k{y}_{i}\left(1-{r}_{i}\right)$$
10
②When \(\theta +\tau >2{c}_{i}\), there is a corner solution.
$${y}_{i}=\frac{\alpha -\delta \beta Y-{kc}_{i}}{\left(2-\delta \right)\beta }, {r}_{i}=1, {q}_{i}={t}_{i}$$
11
Noted that the solution obtained above is not the final solution to the enterprise profit maximization problem.
On the one hand, the \(Y\) on the right side is the summation item of \({y}_{i}\) in the formulas (10) and (11). In other words, \({y}_{i}\) needs to satisfy the condition \(Y={\sum }_{i=1}^{n}{y}_{i}\). On the other hand, \(\theta\) is regarded as an exogenous variable in the above solution process. But in fact,\(\theta\) is determined by the supply and demand of the carbon emission trading market under the given conditions of \(T\) and \(\tau\).
Generally speaking, environmental regulation becomes stricter with the decrease of total emission quota \(T\). Because the supply of emission rights is in short supply, which may drive up the emission trading price \(\theta\). From an industry perspective, emissions trading must meet cap constraints and transaction constraints:
$$\sum _{i=1}^{n}{t}_{i}=T\ge 0, \sum _{i=1}^{n}{q}_{i}=0$$
12
where \(\sum _{i=1}^{n}{t}_{i}=T\) represents the total amount constraint of emission allowances. \(\sum _{i=1}^{n}{q}_{i}=0\) represents the transaction constraint that the quantity of buying and selling is equal.
From the formulas (10) and (11), whether this optimal solution belongs to the internal solution or the corner solution depends on the relationship between \(\theta +\tau\) and \(2{c}_{i}\). When \({c}_{i}={c}_{j}\), the two enterprises belong to the same solution. Whether the solution belongs to the internal solution or the corner solution. From the formulas (10) and (11), we can deduce that as long as \({c}_{i}={c}_{j}\), then \({y}_{i}={y}_{j}\), \({r}_{i}={r}_{j}\) and \({t}_{i}-{q}_{i}={t}_{j}-q\).
Based on the above analysis, the main work is to analyze different types of enterprises, and it is not necessary to conduct separate investigations for all enterprises. From the setting of emission reduction costs, the unit emission reduction cost of the same proportion is only related to the parameter \(c\) for different enterprises. The smaller \(c\) reflects the more advanced pollution control technology of enterprises and vice versa. To simplify the model, we assume that there are only two values of \(c\). According to the difference of \(c\), we divide enterprises into two types: clean enterprises (\(c\) is relatively small, denoted as \({c}_{l}\)) and polluting enterprises (\(c\) is relatively large, denoted as \({c}_{h}\)). Assume that there are \(n\ge 2\) enterprises in total, among which, there are \(m\ge 1\) clean enterprises and \(n-m\ge 1\) polluting enterprises. Here we do not consider the entry and exit of enterprises caused by environmental regulation, so we regard \(n\) and \(m\) as exogenous variables. All enterprises make decisions about production and emission reduction under the given environmental regulations and the number of enterprises.
As mentioned above, the formulas (10) and (11) are not the final solution to the enterprise profit maximization problem. According to the conditions of \(0\le \theta +\tau \le 2{c}_{i}\) and \(\theta +\tau >2{c}_{i}\) in the formulas (10) and (11), the final solution needs to be discussed in four cases, namely \(\theta +\tau =0\), \(0<\theta +\tau \le 2{c}_{l}\), \(2{c}_{l}<\theta +\tau \le 2{c}_{h}\) and \(\theta +\tau >2{c}_{h}\). Details are as follows:
①When \(\theta +\tau =0\),combining with \(\theta \ge 0\) and \(\tau \ge 0\), we could get \(\theta =\tau =0\). According to the solution process of the formulas (10) and (11), we can know that
$${y}_{i}=\frac{\alpha -\delta \beta Y}{\left(2-\delta \right)\beta }$$
13
There is no carbon tax collection and carbon emission trading. At the same time, there is no need to distinguish polluting enterprises from clean enterprises, \(Y=n{y}_{i}\). Thus,
$${y}_{i}=\frac{\alpha }{\left[2+\left(n-1\right)\delta \right]\beta }, Y=n{y}_{i}=\frac{\alpha n}{\left[2+\left(n-1\right)\delta \right]\beta }$$
14
Here, all enterprises are not motivated to reduce emissions, so \({r}_{l}={r}_{h}=0\). Then the total emission quota is
$$T\ge nk{y}_{i}=\frac{n\alpha k}{\left[2+\left(n-1\right)\delta \right]\beta }\equiv \overline{T}$$
15
In this case, the environmental regulation is too loose to have any effect (\(T\ge \overline{T}\)).
②When \(0<\theta +\tau \le 2{c}_{l}\), all enterprises correspond to internal solutions according to the formulas (10) and (11), then
$${y}_{l}=\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)}{\left(2-\delta \right)\beta }, {y}_{h}=\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\beta }$$
16
$${r}_{l}=\frac{\theta +\tau }{2{c}_{l}}, {r}_{h}=\frac{\theta +\tau }{2{c}_{h}}$$
17
Therefore, the total output is
$$Y=m\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)}{\left(2-\delta \right)\beta }+\left(n-m\right)\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)}{\left(2-\delta \right)\beta }$$
18
Further finishing is
$$\left(2-\delta \right)\beta Y=\alpha n-n\delta kY-mk\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)-(n-m)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)$$
,
Simplifying the above formula to get:
$$Y=\frac{\alpha n-mk\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)-(n-m)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)}{\left[2+\left(n-1\right)\delta \right]\beta }$$
19
Taking \(Y\) back to \({y}_{l}\) and \({y}_{h}\), we get
$${y}_{l}=\frac{\alpha \left[2+\left(n-1\right)\delta \right]-\delta \left[\alpha n-mk\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)-(n-m)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)\right]-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)[2+(n-1\left)\delta \right]}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
,
$${y}_{h}=\frac{\alpha \left[2+\left(n-1\right)\delta \right]-\delta \left[\alpha n-mk\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)-(n-m)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)\right]-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)[2+(n-1\left)\delta \right]}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
,
Organizing the formula into:
$${y}_{l}=\frac{\alpha \left(2-\delta \right)+\left[\delta -2-\left(n-m\right)\delta \right]k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)+\left(n-m\right)\delta k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
20
$${y}_{h}=\frac{\alpha \left(2-\delta \right)+m\delta k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)+\left(\delta -2-m\delta \right)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
21
Notice that in this case, the actual emissions of the industry will use up all the emission quotas. So, there will be no remaining emission rights. Otherwise, some enterprises are willing to sell the emission rights under the current trading price. Then, the trading price of emission rights will decrease until all emission rights are used up or \(\theta +\tau\). Therefore,
$$T=mk{y}_{l}\left(1-{r}_{l}\right)+\left(n-m\right)k{y}_{h}\left(1-{r}_{h}\right)$$
22
which is
$$T=mk{y}_{l}\left(1-\frac{\theta +\tau }{4{c}_{l}}\right)+\left(n-m\right)k{y}_{h}\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)$$
23
We have noticed that
$$\frac{\partial T}{\partial (\theta +\tau )}=-\frac{mk{y}_{l}}{4{c}_{l}}-\frac{\left(n-m\right)k{y}_{h}}{4{c}_{h}}<0$$
24
Therefore, we know
$$\underset{\_}{T}\equiv \left(n-m\right)k\left(1-\frac{{c}_{l}}{{c}_{h}}\right)\frac{\alpha \left(2-\delta \right)+\delta m{c}_{l}k+\left(-m\delta -2+\delta \right)(1-\frac{{c}_{l}}{2{c}_{h}})2{c}_{l}k}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }\le T\le \overline{T}$$
25
In this case, the intensity of environmental regulation is moderate. Clean enterprises and polluting enterprises will not sell all the emission allowances, but will choose to keep a part to meet their own production needs (\(\underset{\_}{T}\le T\le \overline{T}\)).
③When \(2{c}_{l}<\theta +\tau \le 2{c}_{h}\), the clean enterprise corresponds to the corner solution, and the polluting enterprise corresponds to the internal solution, then
$${y}_{l}=\frac{\alpha -\delta \beta Y-{c}_{l}k}{\left(2-\delta \right)\beta }, {r}_{l}=1,{y}_{h}=\frac{\alpha -\delta \beta Y-k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\beta },{r}_{h}=\frac{\theta +\tau }{2{c}_{h}}$$
26
The equilibrium output is
$$Y=\frac{\alpha n-m{c}_{l}k-\left(n-m\right)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left[2+\left(n-1\right)\delta \right]\beta }$$
27
$${q}_{l}=\frac{\alpha \left(2-\delta \right)+\left[\delta -2-\left(n-m\right)\delta \right]{c}_{l}k+\left(n-m\right)\delta k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
28
$${q}_{h}=\frac{\alpha \left(2-\delta \right)+\delta m{c}_{l}k+\left(-m\delta -2+\delta \right)k\left(\theta +\tau \right)\left(1-\frac{\theta +\tau }{4{c}_{h}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
29
In this case, the environmental regulations are relatively strict. The emission reduction ratio of clean enterprises reaches 100%, and all emission allowances are sold. Polluting enterprises may purchase emission rights or sell emission rights, depending on their initial emission quotas. But at least some polluting enterprises will purchase emission rights, otherwise the formula (2) is not satisfied.
④When \(\theta +\tau >2{c}_{h}\), according to the formulas (10) and (11), all enterprises correspond to corner solutions. Then according to \(\sum _{i=1}^{n}{q}_{i}=0\) and \({r}_{i}=1\), we can obtain \(T={\sum }_{i}^{n}k{y}_{i}\left(1-{r}_{i}\right)=0\). Here, there will be no emissions, and there will be no emissions trading. Enterprises must reduce all emissions to zero. Therefore, the Lagrange function of the enterprise profit maximization problem is
$${\mathcal{L}}_{i}={y}_{i}\left(\alpha -\beta {y}_{i}-\delta \beta {Y}_{-i}\right)-{c}_{i}k{y}_{i}$$
30
Therefore, we can obtain
$${y}_{i}=\frac{\alpha -\delta \beta Y-{c}_{i}k}{\left(2-\delta \right)\beta }, Y=\frac{\alpha n-m{c}_{l}k-\left(n-m\right){c}_{h}k}{\left[2+\left(n-1\right)\delta \right]\beta }$$
31
We simplify the formula (30) into
$${y}_{l}=\frac{\alpha \left(2-\delta \right)+\left[\delta -2-\left(n-m\right)\delta \right]{c}_{l}k+\left(n-m\right)\delta {c}_{h}k}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }, {r}_{l}=1$$
32
$${y}_{h}=\frac{\alpha \left(2-\delta \right)+\delta m{c}_{l}k+\left(\delta -2-m\delta \right){c}_{h}k}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }, {r}_{h}=1$$
33
In this case, the environmental regulations are so strict that all enterprises cannot emit any emissions. The emission reduction ratio of all enterprises is 100% (\(T=0\)).
3.3 Equilibrium analysis
Based on the analysis of the above four situations, the carbon emission trading market is only meaningful in the case of ②③ (\(0< \theta +\tau <2{c}_{h}\)). Therefore, we limit the environmental regulation to the condition of \(0< \theta +\tau <2{c}_{h}\), and further analyze the equilibrium output.
< 1 > Further analysis of the equilibrium output in Case ②:
$$\frac{\partial Y}{\partial \theta }=\frac{-mk\left(1-\frac{\theta +\tau }{2{c}_{l}}\right)-\left(n-m\right)k\left(1-\frac{\theta +\tau }{2{c}_{h}}\right)}{\left[2+\left(n-1\right)\delta \right]\beta }$$
34
$$\frac{\partial {y}_{l}}{\partial \theta }=\frac{\left(n-m\right)\delta k\left(\frac{\theta +\tau }{2{c}_{l}}-\frac{\theta +\tau }{2{c}_{h}}\right)+(\delta -2)k\left(1-\frac{\theta +\tau }{2{c}_{l}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
35
$$\frac{\partial {y}_{h}}{\partial \theta }=\frac{m\delta k\left(\frac{\theta +\tau }{2{c}_{h}}-\frac{\theta +\tau }{2{c}_{l}}\right)+(\delta -2)k\left(1-\frac{\theta +\tau }{2{c}_{h}}\right)}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
36
From the analysis in Appendix A-1, we can know that \(\frac{\partial Y}{\partial \theta }<0\), \(\frac{\partial {y}_{l}}{\partial \theta }<0\), but \(\frac{\partial {y}_{h}}{\partial \theta }\) may be positive or negative. At the same time, from the formula (22), we have
$$\theta =\frac{2{c}_{l}{c}_{h}}{m{y}_{l}{c}_{l}+\left(n-m\right){y}_{h}{c}_{h}}\left[m{y}_{l}+\left(n-m\right){y}_{h}-\frac{T}{k}\right]-\tau$$
37
$$\frac{\partial \theta }{\partial T}=-\frac{2{c}_{l}{c}_{h}}{k[m{y}_{l}{c}_{l}+\left(n-m\right){y}_{h}{c}_{h}]}, \frac{\partial \theta }{\partial \tau }=-1$$
38
Since \({c}_{l},{c}_{h}>0\), \(m\ge 1\), \(n-m\ge 1\),\(k>0\), so \(\frac{\partial \theta }{\partial T}<0\), \(\frac{\partial \theta }{\partial \tau }<0\).
< 2 > Further analysis of the equilibrium output in the case of ③ (\(2{c}_{l}<\theta +\tau \le 2{c}_{h}\)):
$$\frac{\partial Y}{\partial \theta }=\frac{-\left(n-m\right)\left(1-\frac{\theta +\tau }{2{c}_{h}}\right)k}{\left[2+\left(n-1\right)\delta \right]\beta }$$
39
$$\frac{\partial {y}_{l}}{\partial \theta }=\frac{\left(n-m\right)\delta \left(1-\frac{\theta +\tau }{2{c}_{h}}\right)k}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
40
$$\frac{\partial {y}_{h}}{\partial \theta }=\frac{\left(-m\delta -2+\delta \right)\left(1-\frac{\theta +\tau }{2{c}_{h}}\right)k}{\left(2-\delta \right)\left[2+\left(n-1\right)\delta \right]\beta }$$
41
From the analysis in Appendix A-2, we have \(\frac{\partial Y}{\partial \theta }<0\), \(\frac{\partial {y}_{l}}{\partial \theta }<0\), \(\frac{\partial {y}_{h}}{\partial \theta }<0\). At the same time, the total emissions are:
$$T=\left(n-m\right)k{y}_{h}\left(1-{r}_{h}\right)=\left(n-m\right)k{y}_{h}(1-\frac{\theta +\tau }{2{c}_{h}})$$
42
The formula (42) can be arranged as follows:
$$\theta =2{c}_{h}-\frac{2{c}_{h}T}{\left(n-m\right)k{y}_{h}}-\tau$$
43
$$\frac{\partial \theta }{\partial T}=-\frac{2{c}_{h}}{\left(n-m\right)k{y}_{h}}, \frac{\partial \theta }{\partial \tau }=-1$$
44
Since \({c}_{h}>0\), \(n-m\ge 1\), \(k>0\), \(\frac{\partial \theta }{\partial T}<0\), \(\frac{\partial \theta }{\partial \tau }<0\).
Based on the analysis of the above two cases, \(\frac{\partial Y}{\partial \theta }<0\), \(\frac{\partial {y}_{h}}{\partial \theta }<0\), \(\frac{\partial \theta }{\partial T}<0\),\(\frac{\partial \theta }{\partial \tau }<0\), and the sign of \(\frac{\partial {y}_{l}}{\partial \theta }\) is positive or negative. From \(\frac{\partial \theta }{\partial T}<0\), the emission trading price will decrease with the increase of the industry quota set by the government. With the reduction of the total carbon emission control target \(T\), the carbon emission trading price\(\theta\) will rise.
Notice that we assume that the emission rights’ trading market is cleared, so enterprises can always buy or sell emission rights when they need to trade. Otherwise, the emission rights trading market will not be cleared. The transaction price \(\theta\) will rise or fall. According to \(\frac{\partial Y}{\partial \theta }<0\), it indicates that the increase of the carbon emission trading price r will lead to the decline of the total output \(T\). Therefore, combining \(\frac{\partial \theta }{\partial T}\) and \(\frac{\partial Y}{\partial \theta }\), the government’s environmental regulation becomes stronger, the total output of the entire industry will smaller. Similarly, we can infer that the government’s environmental regulation becomes stronger, the output of polluting enterprises will be smaller. In addition, as the sign of \(\frac{\partial {y}_{l}}{\partial \theta }\) is positive or negative. As environmental regulations become stricter, the output of clean enterprises may decrease or increase. The reason is that although environmental regulations increase the pollution control costs of enterprises, it reflects the relatively clean nature of clean enterprises. So that clean enterprises may increase output to meet the market demand while polluting enterprises reduce production. After two effects are superimposed, the enhanced environmental regulation of \(T\) will lead to the reduction of clean enterprises’ production in some intervals. While the enhanced environmental regulation will lead to an increase of clean enterprises’ production in other intervals. In general, environmental regulation seems to be unfavorable, but it is likely to make clean enterprises better. Because environmental regulation strengthens the advantages of cleaner enterprises.