Carbon Emissions Under Cap-And-trade and Carbon Tax Regulations

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    Production lot-sizing and carbon emissions under cap-and-trade andcarbon tax regulations

    Ping He a , Wei Zhang a , Xiaoyan Xu a, Yiwen Bian b , *

    a School of Management, Zhejiang University, Hangzhou, Zhejiang 310058, PR Chinab SHU-UTS SILC (Sydney Institute of Language & Commerce) Business School, Shanghai University, Shanghai 201800, PR China

    a r t i c l e i n f o

    Article history:

    Received 20 November 2013

    Received in revised form

    28 August 2014

    Accepted 29 August 2014

    Available online 6 September 2014

    Keywords:

    Lot-sizing

    Carbon emission regulation

    Economic order quantity (EOQ)

    a b s t r a c t

    Cap-and-trade and carbon tax are two emission regulations widely used to curb the carbon emissions

    generated from rms. Based on economic order quantity (EOQ) model, this paper examines the pro-

    duction lot-sizing issues of a rm under these two regulations, respectively. The optimal lot-size and

    emissions under the two regulations are achieved. We then investigate the impacts of production and

    regulation parameters on the optimal lot-size and emissions. Furthermore, we compare the rm's

    optimal carbon emissions under the two regulations. It is found that under the cap-and-trade regulation,

    the rm's decisions of the optimal emissions as well as permits trading depend on the differentiated

    permits trading prices. If setup incurs the same cost as holding incurs per unit of generated emissions,

    both regulations always lead to the same optimal emissions (which is also equal to that without emission

    regulation). Otherwise, neither regulation always leads to lower emissions than the other does.

    2014 Elsevier Ltd. All rights reserved.

    1. Introduction

    There is an increasing consensus that the carbon emission

    generated fromrms' activities is one of the main causes of global

    climate change. To curb the carbon emissions, many countries and

    regions enact various regulations on rms' activities. Cap-and-

    trade (or emissions trading)and carbon tax are two most popular

    regulations implemented in the world. Under the cap-and-trade

    regulation,rms initially receive a free amount of permits (cap)

    over a planning horizon (e.g., one year), and are allowed to trade

    the permits with other rms or government agencies through

    special markets (e.g., carbon market). The European Union's

    Emissions Trading System (EU ETS) is the rst and biggest inter-

    national scheme for permits trade. Up to 2010, the EU ETS covers

    11,000 power stations and industrial plants in 30 countries

    (European Commission, 2013), and involves over 50% of all emis-

    sions in the European Union (Benjaafar et al., 2013). Advocated as

    an alternative cost-effective instrument for reducing emissions,

    carbon tax regulation is much easier to implement than cap-and-

    trade regulation is. Under carbon tax regulation, rms are

    charged for their carbon emissions at a constant tax rate level. A

    growing number of scholars (Avi-yonah and Uhlmann, 2009),

    politicians and economists (Inglis and Laffer, 2008) and business

    leaders (Pontin, 2010) advocatecarbon tax regimes rather than cap-and-trade.

    As we know, carbon emissions are generated in almost all ac-

    tivities ofrms, e.g., procurement, production, inventory holding,

    order processing, transportation and some others (Hua et al., 2011;

    Chen et al., 2013). Generally, carbon emissions from different ac-

    tivities are generated in different ways. For example, emissions

    from procurement are generated only when a procurement activity

    is implemented, usually irrelevant to the procured quantity; while

    emissions from inventory holding depend on the inventory quan-

    tity and inventorytime. In production process, if the production lot-

    size is too small (which is advocated by Just-In-Time production

    theory), lots of emissions are generated from frequent setups;

    otherwise, if the production lot-size is too large, lots of emissions

    are generated from inventory. In the presence of emission regula-

    tions, emission-related costs arise in terms of buying additional

    permits (under cap-and-trade regulation) or paying tax (under

    carbon tax regulation). These emission-related costs can be sub-

    stantial (Drake et al., 2010), which induces carbon-intensive rms

    to take the emission-related costs into consideration when deter-

    mining the production lot-size.

    This paper addresses the issues of the production lot-sizing of a

    rm under cap-and-trade and carbon tax regulations based on EOQ

    model. Under each regulation, the optimal lot-size and emissions of

    the rm are characterized, and the impacts of production param-

    eters and regulation parameters on the optimal lot-size and* Corresponding author. Tel.:86 21 69980028; fax:86 21 69980017.E-mail addresses:[email protected],[email protected](Y. Bian).

    Contents lists available atScienceDirect

    Journal of Cleaner Production

    j o u r n a l h o m e p a g e : w w w . e l s e v i e r . co m / l o c a t e / j c l e p r o

    http://dx.doi.org/10.1016/j.jclepro.2014.08.102

    0959-6526/

    2014 Elsevier Ltd. All rights reserved.

    Journal of Cleaner Production 103 (2015) 241e248

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    emissions are also investigated, respectively. Due to their different

    mechanisms, cap-and-trade and carbon tax regulations lead to

    different forms of emissions costs, and have different impacts on

    rms' operational decisions. The comparison of these two regula-

    tions may provide governments the guidance on determining the

    cap (under cap-and-trade regulation) or the tax rate level.

    In the cap-and-trade regulation considered in this paper, the

    permits buying and selling prices of the rm can be different. To our

    bestknowledge, most of the existing studies on operational decisions

    under the cap-and-trade regulation treat these two prices as the

    same. The only exception isGong and Zhou (2013), who investigate

    the impactof emission tradingon a manufacturer's technologychoice

    and production planning by using differentiated permits buying and

    selling prices.Since the emission trade takes place in a carbon market

    and a rm can buy permits from or sell permits to agencies, the

    permits buying price and selling price of a rm could be different.

    FollowingGong and Zhou (2013), we differentiate these two prices

    and assume that the rm's permits buying price is not smaller than

    the rm's permits selling price in the cap-and-trade regulation. The

    rationale for this price differentiation is well-documented in Gong

    and Zhou (2013). First, the trading prices of permits actually repre-

    sent the cost and the revenue of buying and selling a unit of permits,

    respectively, which include transaction costs. Transaction costs inemissions trading can be signicant and have been studied both

    empirically and theoretically (e.g.,Stavins, 1995; Woerdman, 2001).

    Second, the bideask price spreads, often seen in various trading

    markets, are anothercause of non-identical selling and buying prices.

    For instance, the ask and bid prices for ECX EUA (European Union

    Allowances: carbon credits issued under the EU ETS to CO2-emitting

    installations) futures for December 2010 are V15.48 and V14.20 per

    metric ton (12:00 p.m., Aug. 14, 2010, Hong Kong Time), respectively

    (http://www.ecx.eu/market-data). This implies that the rm's per-

    mits buying price may be higher than the selling price in practice.

    Furthermore, we hold that if the buying price is smaller than the

    selling price, rms might raise prot by purely buying and selling

    carbon permits. This speculation in turn weakensthe effect of carbon

    trading regulation on reducingrms' emissions. It is noteworthy that,the production lot-sizing issue with identical permits buying and

    selling prices is a special case of what is discussed in our paper.

    The rest of this paper is organized as follows. In Section 2,

    related literature is reviewed. In Sections 3 and 4, the lot-sizing

    decisions under cap-and-trade and carbon tax regulations are

    explored, respectively. In Section 5, the two regulations are

    compared with respect to the optimal emissions. Section 6 con-

    cludes this paper.

    2. Literature review

    In recent years, the research on cap-and-trade and carbon tax

    regulations has received extensive attentions both in empirical and

    theoretical studies.The rst stream mainly discusses the concepts, advantages and

    disadvantages of cap-and-trade and carbon tax regulations at

    strategic levels based on empirical studies.Ekins and Barker (2001)

    provide a detailed survey of the literature on carbon tax and

    emissions trading as well as their implementations. They conclude

    that there is a general agreement that market-based instruments of

    carbon control will achieve a given level of emission reductions at

    lower cost. As indicatedby Harrison and Smith (2009), the cap-and-

    trade regulation is business-friendly and can produce more jobs.

    However, carbon tax regulation is simpler and easier to implement

    than cap-and-trade regulation is, and the tax increases the revenue

    of government which can be used as the investment of carbon

    abatement (Baranzini et al., 2000). Theoretically, both cap-and-

    trade and carbon tax can achieve cost-effective emission

    reductions (Stavins, 2008), and there is a broad equivalence be-

    tween emissions trading scheme and carbon tax regulation under

    some assumptions (Pezzey, 1992; Farrow, 1995).

    The second stream examines the operational decisions ofrms

    under emission regulations. Letmathe and Balakrishnan (2005)

    study the production mix and production quantities of a rm un-

    der several different environmental constraints, e.g., threshold

    values, penalties and taxes, and/or emissions trading. From the

    perspective of carbon abatement efciency,Mandell (2008)shows

    that utilizing the two regulations (i.e., cap-and-trade and carbon

    tax) can be superior to adopting only one regulation (either cap-

    and-trade or a carbon tax). Benjaafar et al. (2013)introduce a se-

    ries of simple and general models to illustrate howcarbon footprint

    could be incorporated into operational decisions, where many ob-

    servations and insights are obtained. Drake et al. (2010) study a

    two-stage decision problem of a rm under the two regulations

    (cap-and-trade and carbon tax). In the rst stage, the rm chooses

    capacities under two technologies, dirty and clean. With the

    given technology, the rm in the second stage chooses production

    quantities to maximize its own prot.Hoen et al. (2014) examine

    the effect of different emission regulations (including voluntary

    targets) on transportation mode selection for a carbon-aware

    company (either by choice or enforced by regulation) under sto-chastic demand.Jaber et al. (2013)study the coordination in a two-

    level supply chain in the EU ETS, where greenhouse gas emissions

    are generated in the manufacturing processes. Jin et al. (2013)

    investigate the impact of carbon policies on supply chain design

    and logistics of a major retailer, where three carbon policies are

    considered: carbon emission tax, inexible cap and cap-and-trade.

    The third stream is related to the estimation of emission costs and

    carbon accounting under carbon emission regulations. Tsai et al.

    (2012a) develop a mixed Activity-Based Costing (ABC) decision

    model for green airline eet planning under emissions trading

    scheme.Sthls et al. (2011) investigate the impacts of international

    commoditytrade on carbon ows of forestindustry in Finland, using a

    quantitative analysis method. The carbon ows are embodied in the

    tradedforest.They show that in Finland, thedirect impactof theforestindustry is only a minor fraction of the total CO 2emissions related to

    production, and almost all of the emissions are caused due to pro-

    duction of exports. Stechemesser and Guenther (2012) systematically

    review theliterature related to carbon accounting. Onecan refer toTsai

    et al. (2011, 2012b, 2013)and Mozner (2013) for other similar studies.

    Close to our work, Van der Veen and Venugopal (2014) incor-

    porate the cost of energy usage into EOQ model, and nd that the

    economic and environmental performance of a rm can be synergy

    or trade-off, depending on the values of specic parameters of the

    emission regulations. Huaet al.(2011) investigate howrmsreactin

    inventory management under carbon emission regulation based on

    EOQ model. They derive the optimal order quantity, and examine

    the impacts of regulation parameters on the optimal decisions,

    carbon emissions and total costs. However, in their work, only thecap-and-trade regulation is discussed, and the permits buying and

    selling prices are assumed to be equal. Bonney and Jaber (2011)

    incorporate transportation cost and waste into EOQ model, and

    develop an environmental economic order quantity model, which

    results in a larger optimal ordering lot-size than that under the

    standard EOQ model.Arslan and Turkay (2010)revise the standard

    EOQ model by incorporating sustainability constraints. Various

    sustainability constraints, such as carbon tax, cap and trade, direct

    cap andcarbon offset, areconsidered.They show that in most cases,

    the optimal ordering quantity with the presence of sustainability

    constraints is larger than that without the constraints. It is note-

    worthy that, in the above mentioned studies, the permits buying

    and selling prices are all assumed to be the same. One exception is

    Chen et al. (2013). They investigate the EOQ model under various

    P. He et al. / Journal of Cleaner Production 103 (2015) 241e248242

    http://www.ecx.eu/market-datahttp://www.ecx.eu/market-data
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    carbon constraints including carbon tax, carbon offset, and cap and

    price (i.e. cap-and-trade). For each carbon constraint, they show

    whether and howthe ordering quantity can be adjusted to decrease

    rms'costs. Although theymention two prices (award and penalize)

    under cap and price constraint, they do not examine the optimal

    decisions ofrms when these two prices are different.

    Our paper differentiates itself from the existing studies in that it

    treats the permits trading prices to be two different variables and

    assumes that the permit buying price is not smaller than the permit

    selling price. Based on this assumption, some novel insights for

    rms' optimal decisions can be obtained.

    3. Cap-and-trade regulation

    This section examines the optimal production lot-sizing and the

    corresponding optimal carbon emissions under cap-and-trade

    regulation based on EOQ model.

    Consider a carbon-intensive rm which produces a product to

    satisfy the market demand under cap-and-trade regulation. The

    rm rst receives a free quantity of permits (i.e. cap C) on its

    emissions. If necessary, the rm can buy more or sell the granted

    permits through an outside market with unit buying price b andunit selling prices (sb), respectively. Similar toHua et al. (2011)andChen et al. (2013), the variability of buying/selling price over

    time is not considered in this paper. The annual market demand is

    xed atD. Once the rm starts a production run, a setup cost Kand

    related emissionseKare incurred. The unit production cost and the

    corresponding emissions are denoted by c and ec, respectively.

    Assume that the production is instantaneous. Each unit of product

    kept in inventory incurs an annual holding cost h and annual

    emissionseh. The three types of emissions eK,ecand eh, also called

    emission intensities (Drake et al., 2010), relate the production lot-

    size decision to the emissions cost. The objective of the rm is to

    determine the optimal lot-size Q to minimize the sum of produc-

    tion cost, setup cost, holding cost and emissions cost.

    Denote by Ethe total annual emissions of the rm. For given lot-

    sizeQ, the annual setup times is D/Q, thus the emissions generated

    during setups iseKD/Q. The average inventory during a year is Q/2,

    thus the emissions generatedby holding inventory is ehQ/2. Besides

    these two parts, the total annual emissions of the rm also include

    the emissions generated during the production process. Therefore,

    the total annual emissions of the rm is EecDeKD/QehQ/2.Hereafter, the corresponding emissions under the optimal lot-size

    are termed as the optimal emissions.

    Let TCc be the minimal total annual cost under cap-and-trade

    regulation, which can be solved by the following model:

    TCc minQ>0n

    cDKD=QhQ=2 bECsCEo

    ;

    (1)

    where cD KD/Q hQ/2 is the total cost caused by production,setups and inventory holding, and b(E C) s(C E)(u max(u,0)) is the emissions cost (revenue) resulted frombuying or selling permits.

    The following monotonic properties of the optimal total cost can

    be directly obtained from Model(1)(throughout this paper, we use

    increasing and decreasing in the non-strict sense to mean non-

    decreasing and non-increasing, respectively): (i) TCc is

    increasing inc,K,h,ec,eK,eh, respectively; and (ii) TCc is increasing

    in b but decreasing in s. Therefore, in the subsequent sections, we

    do not discuss the above properties, but focus on the properties of

    the optimal decisions, i.e., the optimal lot-size and emissions.

    For ease of analysis, we rst solve the optimal emissions and

    then the optimal lot-size. It is clear that the amount of emissions

    (ecD) associated with production for the xed demand is constant.

    Thus, we focus on the remaining part of the emissions. LetbEEecDeKD=QehQ=2. It is easy to verify thatbE ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp . By solving the equationbEeKD=QehQ=2, wehave two lot-sizes in terms of a function ofbE, i.e.Q1 bE ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffibE2 2eKehDq eh and Q2

    bE ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffibE2 2eKehDq eh:

    Let fbE be the minimal total cost of setups and inventoryholding under givenbE, i.e.fbE min

    eKD=Qeh Q=2bEfKD=QhQ=2g.By substitutingQ1 andQ2 intofbE, we have.

    fbE K=eKh=ehbE.2 jK=eKh=ehj ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffibE2 2eKehDq 2:

    Note that if K/eK h/eh, f

    bE achieves its minimum at Q Q1;

    otherwisef

    bEachieves its minimum at QQ2.K/eK(h/eh) can beinterpreted as the average setup (holding) cost for each unit ofgenerated emissions. For given emissionsbE, K/eK h/eh indicatesthat setup incurs a lower cost than holding does for each unit of

    generated emissions, which leads to more setups with smaller lot-

    size. In contrast, K/eKh/eh leads to fewer setups with larger lot-size. Particularly, ifK/eK< h/ehor K/eK> h/eh, it can be easily veri-

    ed that v2fbE=vbE2 >0, and thus fbE is strictly convex inbE. IfK/eKh/eh, it is clear that vfbE=vbE>0 and v2fbE=vbE2 0, thusfbEis linearly increasing inbE.

    LetbCCecD. Based on the above process, Model(1) can betransformed as:

    TCc min

    nmin

    bEffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp

    ;bEbCTCc1

    bE

    ;

    minbEffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp ;bEbCTCc2bEo; (2)where TCc1bE cDfbE bbEbbC andTCc2bE cDfbE sbEsbCare the costs for the case with buyingpermits bEbC and selling permits bEbC, respectively. Note thatthe overall emissions arebEecD.

    We next develop the optimal lot-size and the optimal emissions

    based on Model(2). Dene the following thresholds:

    Cdargmin

    bE>0

    nfbEbbEo and Cdargmin

    bE>0

    nfbE sbEo:

    Since b s, it isclearthat CCbased on the convexity offbE. NotethatCCifbs. Denote bybEc the optimal solution to Model(2).Based on the convexity offbE, we have the following result.Lemma 1. The thresholds C and C satisfy:

    CK=eKh=eh 2bffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eKbh=ehbp ; and C

    K=eKh=eh 2sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eKsh=ehsp ;

    with CC

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p , and

    bE

    csatises that

    bE

    c C when

    bCC.

    P. He et al. / Journal of Cleaner Production 103 (2015) 241e248 243

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    TheProof of Lemma 1(and all subsequent results) can be found

    in the Appendix part. Lemma 1 shows the values ofbEc underdifferentbC. In particular, the buying and selling prices (of thepermits) determine the lower bound Candthe upperbound CofbEc,respectively. A larger difference between b and s implies a wider

    span betweenCand C.

    Now, we characterize the optimal solution to Model(1). Denote

    by Qc

    andEc

    the optimal lot-size and emissions under the cap-and-

    trade regulation, respectively. Based on Lemma 1, we have the

    following theorem:

    Theorem 1. Under the cap-and-trade regulation,

    (i) when C< ecDC, the optimal emissions are Ec ecDC, andthe optimal lot-size is Q

    c ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2KbeKD=hbehp

    ;

    (ii) when ecDCCecDC, the optimal emissions are equalto the cap, i.e., E

    c C, and the optimal lot-size satises:(a) if K/eK h/eh, then Q c CecDffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    CecD2 2eKehDq

    =eh,(b) if K/eK h/eh, then Q c CecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCecD2 2eKehDq =eh;(iii) when C> ecDC, the optimal emissions are Ec ecDC andthe optimal lot-size is Q

    c ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KseKD=hsehp .Based on Theorem 1, we know that the emissions E

    care

    increasing (fromecDCtoecDC) in the capC. Recall inLemma 1that ifbs, thenCC, which implies that the optimal lot-size andemissions are independent of cap C. The rationale is that the im-

    pacts of emissionsEunder different levels of cap Con the total cost

    are the same when b s (the emissions trading cost can beexpressed as the sum of two separate linear functions ofEand C,

    respectively). Note that the optimal emissions are increasing in ec,

    but independent of the unit production cost c.

    Theorem 1 also shows the optimal decision for emissions

    trading. It is optimal to buy C

    ecD

    C unit permits when

    C< ecDC, to buy and sell nothing when ecDCCecDC,and to sell CecDC unit emissions when C> ecDC. Theresulted permits range (ecDCto ecDC) is ultimately the rangeof the actual amount of emissions. The determination of the two

    thresholds on the rm's emissions depends on the permits

    buying price and selling price, respectively. The lower threshold

    decreases in the permit buying price, and the upper threshold

    decreases in the permit selling price. The larger the difference

    between permits buying price and selling price is, the larger the

    range between these two thresholds is. It is noteworthy that the

    difference between the permit buying price and selling price in

    this paper can be regarded as the transaction cost.

    Particularly, if these twoprices are thesame,as assumed in many

    existing studies, thermwill alwaysbuy or sell some permits unless

    the initial cap equals a special value, i.e. CecDCecDC. Thismeans, the optimal emissions of the rm will always be a xed

    amount, which is determined by the permits trading prices but not

    the rm's received free permits.

    Based on Theorem 1, we derive the impacts of regulation pa-

    rameters (i.e.,C,s and b) on the optimal emissionsEc, as shown in

    Proposition 1.

    Proposition 1. Under the cap-and-trade regulation,

    (i) if K/eK h/eh, then the optimal emissionsare independent of C, sand b, and E

    cecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p ;

    (ii) if K/eKs h/eh, then the optimal emissions are increasing in C,

    but decreasing in s and b, respectively.

    Proposition 1(i) indicates that if setup incurs the same cost as

    holding does for each unit of generated emissions, then the cap-

    and-trade regulation has no direct impact on the rm's optimal

    amount of emissions. The reason for this is that, the optimal lot-

    size also minimizes the carbon emissions, so the rm should

    keep the lot-size without engaging in carbon trade. However, if

    setup incurs a lower or higher cost than holding does for each

    unit of generated emissions, in the presence of smaller cap,

    higher buying or selling prices, the rm will have more in-

    centives to decrease its emissions, as indicated in Proposition

    1(ii).

    The following proposition characterizes the impacts of regu-

    lation parameters on the optimal lot-sizeQc. Denote by Q* theoptimal lot-size in the classic EOQ model without the emissions

    regulation, then Q*

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KD=h

    p . We have the following results

    about the comparison of the optimal lot-sizes.

    Proposition 2. By comparing Qc

    with Q*

    , wend:

    (i) if K/eK h/eh, then Qc is independent of C, s and b, andQ

    c

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKD=eh

    p

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KD=h

    p Q*;

    (ii) if K/eK < h/eh, then Qc>Q

    *

    , and Qc

    is decreasing in C but

    increasing in s and b,respectively;(iii) if K/eK > h/eh, then Q

    c

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    TCt minQ>0fcDKD=QhQ=2 tEg; (3)

    where tEis emissions cost (i.e. the tax).

    The following monotonic properties of the optimal total cost

    can also be directly obtained from Model (3): (i) TCt is increasing

    in c, K, h , e c, eK, e h, respectively; and (ii) TCt is increasing in t.

    Comparing the emissions cost under Model (3)with that under

    Model(1), it is clear that carbon tax regulation is equivalent to cap-and-trade regulation with C0 andbt, whiles can be any valuesmaller than b because there is no permits to be sold in carbon tax

    regulation (or equivalently C 0).Thus in thissection we directly givethe optimal decisions of the rm under the carbon tax regulation.

    Denote by Qt

    and Et

    the optimal lot-size and the optimal

    emissions under the carbon tax regulation, respectively. By setting

    C0 and b t, the values and properties of the optimal lot-sizeand emissions under the carbon tax regulation are given in Theo-

    rem 2. Theorem 2 can be directly obtained based on Theorem 1 and

    Propositions 13, and thus its proof is omitted for brevity.

    Theorem 2. Under the carbon tax regulation, the optimal lot-size

    and emissions satisfy:

    Qt ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KteKD=h tehq ; EtecDK=eKh=eh 2t

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eK th=ehtp ; and

    (i) if K/eK h/eh, both the optimal lot-size and emissions are in-dependent of t, with Q

    t

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKD=eh

    p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KD=hp Qc,E

    t EcecDffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    ;

    (ii) if K/eK s h/eh, the optimal emissions are decreasing in t.

    Particularly, if K/eK< h/eh, the optimal lot-size is increasing int,

    while if K/eK> h/eh,the optimal lot-size is decreasing in t;

    (iii) the optimal lot-size is increasing in K but decreasing in h.

    Particularly,if K/eKh/eh,the optimal emissions are increasingin K but decreasing in h; if K/eKh/eh, the optimal emissionsare decreasing in K but increasing in h.

    Theorem 2 shows the optimal lot-size and emissions under

    the carbon tax regulation, and summarizes the impacts of pro-

    duction and regulation parameters on the optimal decisions. By

    comparing Theorem 2(iii) with Proposition 3, we nd that the

    impacts of production parameters (i.e. K and h) on the optimal

    lot-size and emissions are the same under the both regulations.

    Similar to the discussion of the cap-and-trade regulation, if setup

    incurs the same cost as holding does for each unit of generated

    emissions, then the rm's optimal lot-size under the carbon tax

    regulation is also equal to the solution to the classic EOQ model

    without the emission regulations.Based onLemma 1,Theorems 1 and 2, we can derive a condi-

    tion under which the optimal decisions under the two regulations

    are the same. Based on Lemma 1andTheorem 2, we nd that if

    t b, Et CecD; if t s, Et CecD; if t b s,E

    t CecDCecD. Hence, by further comparing Theorem 1with Theorem 2, we know that when t b s, both theoptimal lot-size and emissions under the carbon tax regulation

    are the same as those under the cap-and-trade regulation,

    respectively, which are irrelevant to any capC.

    5. Comparison of the optimal emissions

    Due to their different mechanisms, cap-and-trade and carbon

    tax regulations may have different impacts on

    rms' performance,

    especially on the optimal emissions. Based on Theorems1 and 2, we

    have the following results about the optimal emissions of the rm

    under cap-and-trade and carbon tax regulations.

    Theorem 3. Under cap-and-trade and carbon tax regulations,

    (i) if K/eKh/eh,both the two regulations have no impact on theoptimal emissions, and E

    tE

    cecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp ;(ii) if K/eKs h/eh,the optimal emissions under two regulations Et

    and Ec

    satisfy:

    (a) if t > b,EtEc when CE

    cfor all C.

    Theorem 3indicates that, the difference between the optimal

    emissions of the rm under two regulations depends on not only

    the regulation parameters (i.e., C, s, b, t) but also the intrinsic

    production parameters of the rm (i.e.,K,h,eh,eK).

    Note that the buying price of permits under cap-and-trade

    regulation determines the lower bound of

    bE

    cand thus of E

    c

    (see Lemma 1). If the tax rate level is higher than the buying

    price of permits, the emissions should be even lower than thelower bound ofE

    c. If the tax rate level is lower than the selling

    price of permits, the emissions should be even higher than the

    upper bound ofEc. If the tax rate level is between the range of

    the buying and selling prices of permits, the relative magnitude

    of the optimal emissions under these two regulations depends on

    the initial capC. Therefore, none of these two regulations leads to

    lower emissions than the other does all the time.

    To further elaborateTheorem 3, a numerical example is con-

    ducted. To this end, let D90,000,c20, K200,h2, ec2,eK 25, e h 0.5, s 3 and b 7. The optimal emissions of therm with different caps (under cap-and-trade regulation) and

    with different tax rate levels (under carbon tax regulation) are

    depicted inFig. 1.

    The straight lines inFig. 1denote the optimal emissions of the

    rmEt under the carbon tax regulation with different tax ratelevels. The polygonal line denotes the optimal emissions of the

    rm Ec under the cap-and-trade regulation. The caps corre-sponding to the two ex points on the polygonal line are CecDand CecD, respectively. Note that in this example, K/eK 200/258, andh/eh2/0.54, thusK/eKs h/eh. As shown inFig. 1, ift2, i.e. ts,Et is greater thanEc over all levels of capC. Ift8,i.e. t b, Et is less than Ec over all levels of cap C. If t 5, i.e.s < t < b,E

    tis greater thanE

    cwhen the capCis less thanE

    t, andE

    t

    is less than Ec

    when the capCis greater than Et. These results are

    consistent with the conclusions inTheorem 3(ii).

    Fig. 1. The optimal emissions under the two regulations.

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    6. Conclusions

    This paper addresses the production lot-sizing issues of a rm

    under cap-and-trade and carbon tax regulations based on EOQ

    model. We characterize the optimal lot-size and corresponding

    (optimal) emissions under each regulation, and compare the

    performance of the rm with respect to the optimal carbon

    emissions under the two regulations.

    Our results show that, under the cap-and-trade regulation,

    the rm may buy some permits for production, or sell some

    surplus permits, or buy and sell no permits at all, depending on

    the value of initial cap. If setup incurs the same cost as holding

    incurs per unit of generated emissions, both regulations always

    lead to the same optimal emissions (which is also equal to that

    without emissions regulation). Otherwise, neither regulation al-

    ways leads to lower emissions than the other does.

    In this work, we only consider the lot-size and emissions

    decisions in one particular period, and thus assume that the

    permits buying and selling prices do not change over time. This

    modelling and analysis is appropriate for those carbon-intensive

    rms with small or modest carbon emissions, especially for those

    producing single-period products such as food and electricity,

    which are more likely to buy or sell permits on the spot market.Firms with large carbon emissions are likely to make permits

    trading actions by taking actual production into account, multi-

    ple period analysis may be more appropriate. On the other hand,

    we focus our research on a single rm's decision making and do

    not consider multiple competitive rms. These aspects are the

    main limitations of our work, which can be further examined in

    future research. Furthermore, more research can also be done in

    the following ways. First, the decision problem can be investi-

    gated based on other models, e.g. newsvendor model. Stochastic

    demand can be more realistic and may generate some other in-

    sights. Second, the decision-making of the government can be

    incorporated. The rm and the government take part in a deci-

    sion game, with the objective of minimizing the total cost of the

    rm and maximizing the social welfare, respectively.

    Acknowledgements

    This research was supported by the National Natural Science

    Foundation of China (nos. 71001094, 71101085, 71201153,

    71371176), NSFC Major Program (nos. 71090401/71090400), and

    Innovation Program of Shanghai Municipal Education Commis-

    sion (no. 12ZS099). The authors thank the editor and three ref-

    erees for helpful comments and suggestions on the earlier

    manuscript.

    Appendices

    Proof of Lemma 1

    It is clear that CdargminbE>0ffbE bbEg can be found bycomputing the corresponding emissions when the lot-size is the

    solution to the following problem.

    minQ>0fKD=QhQ=2 beKD=QehQ=2g;

    whereKD/QhQ/2 is the sum of setup and inventory holding cost,andbEeKD=QehQ=2. It is clear that the optimal solution for theabove problem is

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KbeKD=hbeh

    p . Hence the correspond-

    ing emissions satisfy

    CK=eKh=eh 2bffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eKbh=ehbp

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2ekehDp K=eKb h=ehb

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eKbh=ehbp ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp :

    Similarly, we have

    CK=eKh=eh 2sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eKsh=ehsp

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2ekehDp K=eKs h=ehs

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK=eKsh=ehsp

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p :

    Recall thatCCfrom the convexity off(z). Consequently, we haveCC ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp .

    Dene

    bE

    c

    1dargmin

    bEffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp

    ;bEbCnf

    bE

    b

    bE

    o and

    bE

    c

    2

    argminbEffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp ;bEbCnfbEsbEo:Since CdargminbE>0ffbE bbEg and CdargminbE>0ffbE sbEg,we havebEc1maxC;bC andbEc2minbC; C based on the con-vexity offbE. Consequently, we have

    (i) whenbCC,bEc1bCandbEc2C. SincebCis a feasible solutionto minbEffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp ;bEbCffbE sbEg, we haveTCc cDfC sCsbCcDfC sCecDC.

    Proof of Theorem 1

    (i) and (iii) can be easily veried from Lemma 1. Details are

    omitted for brevity. We next prove (ii). When

    ecDCCecDC, we have C

    bCC, and thus

    E

    c

    ecDbEc ecDbC C, and the feasible lot-sizes areCecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCecD2 2eKehD

    q =eh. Substituting these lot-sizes

    in Model(1), we have the total costs are.

    cDK=eKh=ehCecD=2h=ehK=eK

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCecD2 2eKehD

    q 2:

    Consequently, if K/ek h/eh,Q

    c CecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    CecD2 2eKehDq

    =eh, and if K/ek h/eh,Q

    c CecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCecD2 2eKehD

    q =eh.

    It can be veri

    ed that

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    Cffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    C2 2eKehDq

    ehK=eKh=eh 2bjK=eKh=ehj

    2K=eKbffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KbeKD

    hbeh

    s ;

    C ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC2

    2eKehDq eh K=eKh=eh 2sjK=eKh=ehj2K=eKsffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2KseKDhseh

    s :

    Hence, we have that ifK/ekh/eh,0@C ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC2 2eKehDq 1A,eh ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KbeKD=hbehq

    andC

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC

    2 2eKehDq

    ehffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2KseKD=hsehq

    ;

    and ifK/ekh/eh,0@C ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC2 2eKehDq 1A,eh ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KbeKD=hbehq ;

    andC

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC

    2 2eKehDq

    ehffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2KseKD=hsehq

    :

    So we have that if K/eK h/eh,Q

    c Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    Ec ecD2 2eKehDq

    =eh, otherwise

    (K/eKh/eh),Qc

    Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiEc ecD2 2eKehDq =eh. Proof of Proposition 1

    IfK/eK h/eh, thenLemma 1indicates that CCffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    .

    Hence, the optimal emissions are a constant, i .e.,

    EcecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p . So (i) holds.

    (ii) can be proved from the following process. Theorem 1

    directly indicates that Ec

    is increasing in C. Specically, Ec

    is

    increasing from ecDC to ecDC. Recall thatCdargminbE>0ffbE bbEg and CdargminbE>0ffbE sbEg. Conse-quently, the convexity of f(z) indicates that C(C) is decreasing in

    b(s). So we have thatEc

    is decreasing ins and b; respectively.

    Proof of Proposition 2

    Recall that EcecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehD

    p if K/eK h/eh. Since

    Qc Ec ecD

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiEc ecD2 2eKehD

    q =eh (from the Proof of

    Theorem 1), we have that Qc

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKD=eh

    p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2KD=hp Q* ifK/eKh/eh.

    We next prove (ii) and (iii). Dene

    g1zdzffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    z2 2eKehDq

    and g2zdzffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    z2 2eKehDq

    :

    It is clear thatg1(z)d 2eKehD/g2(z). Sinceg2(z) is increasing inz,

    we have g1(z) is decreasing in z. This indicates that

    Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    Ec ecD2 2eKehDq

    =eh is decreasing in Ec ecD,

    while Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    Ec ecD2 2eKehDq

    =eh is increasing inE

    c ecD.Proposition 1(ii) shows thatEc is increasing inCwhile it isdecreasing in s and b, respectively. So we have that ifK/eK< h/eh,

    thenQc

    is decreasing inC, but is increasing ins andb, respectively,

    and ifK/eK> h/eh, thenQc

    is increasing inC, but is decreasing in s

    andb, respectively.

    Proof of Proposition 3

    We rst show the monotonic properties of the optimal emis-

    sions because we have shown the impact of the optimal emissions

    on the optimal lot-size in theProof of Proposition 2.

    Denote

    Rv K=eKh=eh 2vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eK vh=ehvp

    ffiffiffiffiffiffiffi

    2Dp

    2

    KehheK 2veKeh

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiKveKh veh

    p :

    It is clear that CRband CRs. SincevRvveK

    ffiffiffiffiffiffiffi

    2Dp

    2

    K2h 3veh veKh 2veh2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    KveK3h vehq >0

    and

    vRvveh

    ffiffiffiffiffiffiffi

    2Dp

    2

    h2K 3veK vehK 2veK2

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiKveKh veh3

    q >0;we have bothCand Care increasing ineKandeh, respectively. Note

    that both Cand Care clearly independent of. ec.

    The impacts ofKand h on Cand Ccan be veried as follows. R(v)

    can be rewritten as.

    Rvffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK=eK v

    pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih=ehv

    p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih=ehvpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK=eK v

    p !

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    2eKehDp

    2 r

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK=eK v

    pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih=ehv

    p !;wherer(t)t1/t. It is clear thatr(t) is decreasing when t1, butis increasing whent1. Consequently, we have that: ifK/eKh/eh,R(v) is increasing inKbut is decreasing inhfor allv, and ifK/eKh/eh, R(v) is decreasing in decreasing in Kbut is increasing in h for all v.

    CRb and CRs indicate that the cost parameters K and hhave the same impacts on Cand C.

    Now, we have that (i) bothCand Care increasing in eKand eh,

    respectively, but are independent of ec; and (ii) if K/eK h/eh,both Cand Care increasing in Kbut is decreasing in h , and ifK/

    eK h/eh, is decreasing in Kbut is increasing in h .FromTheorem 1, we have

    Ec

    8>:ecDC; C< ecDCC; ecDCCecDCecDC; C> ecDC

    Hence, Ec

    is increasing in ec, C and C, respectively, for all C. The

    above impacts of parameters on C and C indicate that: (i) the

    optimal emissions are increasing in ec, eK and eh, respectively,

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    and (ii) ifK/eK h/eh, the optimal emissions are increasing in Kbut is decreasing in h, and ifK/eK h/eh, the optimal emissionsare decreasing in decreasing in Kbut is increasing in h. Conse-

    quently,Proposition 3(ii, iii) hold.

    From the Proof of Theorem 1 and Proof of Proposition 2, we

    have that if K/eK h/eh,Q

    c Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiE

    c ecD2 2eKehDq =eh is decreasing inEc ecD, and if K/ek h/eh,Q

    c Ec ecD ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    Ec ecD2 2eKehDq

    =eh is increasing inE

    c ecD. Consequently, the impacts of K and h on the optimalemissions E

    cindicate that the optimal lot-size is increasing in K

    but is decreasing in. h .

    Proof of Theorem 3

    Part (i) can be directly veried from Proposition 1(i) and

    Theorem 2(i). We next discuss the optimal emissions under the

    two regulations whenK/ek s h/eh. Recall that the emissions under

    the two regulations are

    Ec

    8>:ecDC; C< ecDCC; ecDCCecDCecDC; C> ecDC

    and

    Et ecDK=eKh=eh

    2t ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2eKehDp2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    K=eK th=ehtp : (A.1)

    It can be veried thatEt ecDargminbE>0ffbE tbEg. Recall that

    fbEis strictly convex ifK/eKs h/eh. Consequently, (1) ift > b, thenE

    t ecDC. Based on the above three points, part (ii) holds fromEquation(A.1).

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