Proterra SPAC Presentation Deck

INTRODUCTION Disclaimer (Cont'd) PROTERRA Additional Information In connection with the proposed Business Combination, ArcLights filed on February 2, 2021 with the SEC a registration statement on Form S-4 containing a preliminary proxy statement/prospectus of ArcLight, and after the registration statement is declared effective, ArcLight will mail a definitive proxy statement/prospectus relating to the proposed Business Combination to its shareholders. This Presentation does not contain all the information that should be considered concerning the proposed Business Combination and is not intended to form the basis of any investment decision or any other decision in respect of the Business Combination. ArcLight's shareholders and other interested persons are advised to read the preliminary proxy statement/prospectus and, when available, the amendments thereto and the definitive proxy statement/prospectus and other documents filed in connection with the proposed Business Combination, as these materials will contain important information about the Company, ArcLight and the Business Combination. When available, the definitive proxy statement/prospectus and other relevant materials for the proposed Business Combination will be mailed to shareholders of ArcLight as of a record date to be established for voting on the proposed Business Combination. Shareholders will also be able to obtain copies of the preliminary proxy statement/prospectus, the definitive proxy statement/prospectus and other documents filed with the SEC, without charge, once available, at the SEC's website at www.sec.gov, or by directing a request to: ArcLight Clean Transition Corp., 200 Clarendon Street, 55th Floor, Boston, MA 02116. Financial Information Certain of the financial information and data contained in this Presentation is unaudited and does not conform to Regulation S-X promulgated under the Securities Act of 1933, as amended (the "Securities Act"). Accordingly, such information and data may not be included in, may be adjusted in or may be presented differently in, the registration statement filed by ArcLight and Proterra with the SEC. Participants in the Solicitation ArcLight, the Company and their respective directors and executive officers may be deemed participants in the solicitation of proxies from ArcLight's shareholders with respect to the proposed Business Combination. A list of the names of ArcLight's directors and executive officers and a description of their interests in ArcLight is contained in ArcLight's final prospectus relating to its initial public offering, dated September 22, 2020, which was filed with the SEC and is available free of charge at the SEC's web site atwww.sec.gov, or by directing a request to ArcLight Clean Transition Corp., 200 Clarendon Street, 55th Floor, Boston, MA 02116. Additional information regarding the interests of the participants in the solicitation of proxies from ArcLight's shareholders with respect to the proposed Business Combination will be contained in the definitive proxy statement/prospectus for the proposed Business Combination when available. No Offer or Solicitation This Presentation shall not constitute a "solicitation" as defined in Section 14 of the Securities Exchange Act of 1934, as amended. This Presentation does not constitute an offer, or a solicitation of an offer, to buy or sell any securities, investment or other specific product, or a solicitation of any vote or approval, nor shall there be any sale of securities, investment or other specific product in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of the Securities Act. Trademarks and Trade Names Proterra and ArcLight own or have rights to various trademarks, service marks and trade names that they use in connection with the operation of their respective businesses. This Presentation also contains trademarks, service marks and trade names of third parties, which are the property of their respective owners. The use or display of third parties' trademarks, service marks, trade names or products in this Presentation is not intended to, and does not imply, a relationship with the Company or ArcLight, or an endorsement or sponsorship by or of the Company or ArcLight. Solely for convenience, the trademarks, service marks and trade names referred to in this Presentation may appear with the Ⓡ, TM or SM symbols, but such references are not intended to indicate, in any way, that the Company or ArcLight will not assert, to the fullest extent under applicable law, their rights or the right of the applicable licensor to these trademarks, service marks and trade names. Summary of Contracts Insofar as this Presentation contains summaries of existing agreements and documents, such summaries are qualified in their entirety by reference to the agreements and documents being summarized. April 8, 2021 3

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