Shannon is a trusted advisor to her clients, who describe her as an “outstanding lawyer—very practical, effective, extremely smart and incredibly knowledgeable,” in Chambers USA, 2016.

Shannon is the managing partner of the firm’s San Francisco office and leads the firm’s California environmental practice. Her prior experience as a chemical engineer in the oil and gas industry affords her unparalleled insights into the development of regulations and counsel on environmental, health and safety issues. Shannon also maintains an office in Washington, DC. Splitting her time between these offices allows her to help her clients wherever they may be. Her work focuses on permitting, enforcement, environmental incident response, and regulatory advocacy and litigation.

Shannon is a nationally recognized authority on Clean Air Act and climate change matters, with more than 25 years of experience addressing all aspects of the Clean Air Act, Shannon represents clients in a variety of manufacturing and energy sectors, including oil and gas, chemical, paper, automotive, power generation and utilities. Related to her climate practice and environmental matters generally, Shannon is credentialed by the Sustainability Accounting Standards Board in the Fundamentals of Sustainability Accounting, which supports her practice advising companies on Environmental, Social, and Governance (ESG) issues and disclosures. Shannon also advises companies in preparation for and responding to environmental incidents and under federal and state process safety management and risk management plan regulations.

Highly regarded for her litigation practice challenging and defending EPA and California regulations and permits before federal and state appellate courts, in 2018, she was named to The National Law Journal’s list of “Energy & Environmental Trailblazers.” She has been repeatedly named to the California Daily Journal’s list of Top 100 Women Lawyers and Top 100 Lawyers. She is one of four lawyers nationally ranked by Chambers USA in Band 1 for Nationwide Climate Change and is also ranked by Chambers in California Environment and Global Climate Change law. In 2019, Broome was appointed for a three-year term by the Administrator of the US EPA to the Clean Air Act Advisory Committee, which advises the EPA on appropriate implementation of the statute. She is also lauded for her deep knowledge on environmental enforcement matters, and is respected by her Fortune 100 clients for her practical approach to regulatory compliance, in which she relies on her previous career as an engineer for Chevron, USA.

Shannon is admitted in the United States Supreme Court, US Courts of Appeals for the District of Columbia, First, Fourth, Fifth, Ninth, and Tenth Circuits, several US District Courts, and all California state courts.

Outside of her client work, Shannon devotes herself to improving diversity and inclusion in the legal profession. She is the current and founding Co-President of the California chapter of the Women’s Energy Network. As an accomplished female lawyer and previous engineer, Shannon is a frequent speaker on issues related to how women can succeed in the workplace, particularly in the legal profession. She was appointed to and is currently serving as a leader on the American Bar Association’s Special Committee on Diversity, Equity, and Inclusion of the Section of Environmental, Energy, and Resources Law, which addresses among other things, racial and gender inclusion and equity issues in the legal field, and serves on the Section’s governing council. Shannon also volunteers her time as a Berkeley Law School Alumni Guide, a role in which she mentors young female law students.

Shannon is a contributor to the firm’s environmental blog, The Nickel Report.

Relevant Experience

  • Represents oil and gas company client in climate change litigation in California, in claims by cities and counties that her client, along with other oil and gas companies, is liable under state common law nuisance theories.
  • Represents Fortune 500 companies on Environmental, Social, and Governance (ESG) issues and on related corporate disclosures and reporting.
  • Represents oil companies in complex Clean Air Act permitting and enforcement under the Prevention of Significant Deterioration, Nonattainment New Source Review, minor source, and Title V permitting programs.
  • Represents major mobile fleet operator in enforcement of California Air Resources Board onroad and off-road emissions regulations.
  • Represented major construction equipment manufacturer in resolving enforcement action under Clean Air Act Title II, related to import and marketing in the United States.
  • Represents numerous off-road and light and heavy duty vehicle manufacturers on compliance with Title II federal regulations and California Air Resources Board regulations.
  • Represents companies subject to the California Low Carbon Fuels Standard (LCFS) and federal Renewable Fuels Standard (RFS) programs on compliance requirements and in enforcement actions.
  • Represents an industry trade association on EPA’s revision of its risk management plan (RMP) regulations for chemical accidents, including arguing in defense of a regulation issued by the Pruitt EPA to delay the prior administration’s RMP regulatory revisions before the U.S. Court of Appeals for the D.C. Circuit.
  • Represents major trade groups, including auto industry, oil and gas, chemical, aerospace, steel, and general manufacturing trade associations, before EPA on Clean Air Act rulemakings, including litigating dozens of such regulations in the U.S. Court of Appeals and arguing in the D.C. Circuit in both challenging and defending Clean Air Act rules.
  • Represents the steel industry, the auto industry, and turbine manufacturers, among others, in rulemaking to address residual risk and technology reviews under Clean Air Act Section 112.
  • Represented refinery in incident response to air and ground release that created vapor cloud over resort community, including managing release reporting, permitting implications, and coordination of communication with state and federal regulators.
  • Represented refinery in interface with federal and state regulators in light of significant equipment malfunction with potential to lead to several days of flaring.
  • Represents several refineries and upstream oil and gas operations in permitting and enforcement actions before California air districts.
  • Represents major oil trade association in regulatory advocacy before EPA and in the US Court of Appeals for the DC Circuit related to the agency’s regulations of upstream and midstream emissions of volatile organic compounds and methane.
  • Represented midstream oil and gas company in enforcement action in northwest state over environmental and Army Corps of Engineers permitting requirements.
  • Represented major household product manufacturer in environmental enforcement of the Clean Air Act.
  • Represents major automobile manufacturer on all air permitting and enforcement for its manufacturing plants in Michigan, Indiana, New York and Illinois.
  • Represents major automobile company on EPA greenhouse gas and National Highway Transportation Safety Administration on corporate average fuel economy (CAFE) standards.
  • Represented major oil company on regulatory advocacy on Clean Air Act regulation under Section 112(f) for residual health risk, achieving resolution that saved the company tens of millions of dollars.
  • Represented trade association in litigation challenging California’s Low Carbon Fuel Standard (LCFS) in US district court, the US Court of Appeals for the Ninth Circuit and the Supreme Court.
  • Represented coalition of 20 trade associations in eight challenges to EPA’s greenhouse gas regulatory approach in the US Court of Appeals for the District of Columbia Circuit, which is now awaiting the Supreme Court’s determination as to whether to grant certiorari.
  • Represented utility in enforcement before California air district, negotiating favorable settlement of same.
  • Represented joint venture in achieving passage of legislation in California allowing for treatment of on-board recycled oil without treating it as disposal of hazardous waste.
  • Represented major manufacturing company on Waxman-Markey climate change cap-and-trade legislation.
  • Represented investor group in large utility unit in negotiating transaction terms related to environmental compliance obligations under Mercury Air Toxics Rule and other regulatory requirements.
  • Represented Texas Oil & Gas Association in litigation in the US Court of Appeals for the District of Columbia Circuit, challenging EPA’s New Source Performance Standards for Oil and Gas operations (fracking).
  • Represented Midwest manufacturing facility on Clean Air Act permitting, successfully obtaining permit in the face of initial modeling indicating violation of ambient air quality standards.


  • Co-President, Women’s Energy Network of California (2020-2022)
  • Special Committee on Diversity, Equity, and Inclusion, American Bar Association Section on Energy, Environment, and Resources
  • Governing Council Board Member 2019-2022 term, Immediate Past Chair Climate Change Committee, Vice-chair, Climate Change Committee and Air Quality Committee, American Bar Association’s Section on Energy, Environment, and Resources
  • Executive Director, Air Permitting Forum
  • Executive Director, Auto Industry Forum
  • Co-chair, Climate Change, Sustainable Development, and Ecosystems Committee, American Bar Association’s Section on Energy, Environment, and Resources, 2013–2016
  • Vice-chair, Programming of the Air Quality Committee, American Bar Association’s Section on Energy, Environment, and Resources, 2011–present
  • Member, Environmental Law and Public Law Sections of the California Bar Publications

Awards & Recognition

  • Recommended for Environment: Litigation (2017-2022), Environment: Regulatory (2019-2022), Energy Litigation: Oil and Gas (2020-2022) and Energy Regulation: Oil and Gas (2020-2022), Legal 500 United States
  • Recognized as the Environmental/Natural Resources Litigator winner at the Benchmark Litigation US Awards, 2022

  • Recognized as a Leader in Climate Change, Global-wide, Chambers Global, 2019-2022
  • Recognized as 2021 Environmental Group of the Year, Law360, January 2022
  • Recognized as a Leader in Climate Change, USA-Nationwide, Chambers USA, 2012-2022
  • Recognized as a Leader in Environment in California (2017-2022) and District of Columbia (2012-2016), Chambers USA
  • Named among the Top Women Lawyers in California, Daily Journal, 2014, 2017, 2018, 2020-2022
  • Named among the Top 100 Lawyers in California, Daily Journal, 2014, 2019, 2021
  • Recognized as an Energy and Environmental Trailblazer, National Law Journal, 2018 (career-based award)
  • Selected as a member of the Lawdragon Top 500 Environmental and Energy Lawyers, 2021
  • Recognized as Leader for Environment - Climate Change 2020, Who’s Who Legal, September 2020
  • Named an MVP in Environment, Law360, 2019
  • Recognized as a Leader for Environmental Law, Who’s Who Legal (12th Edition), May 2018
  • Recognized as 2017 Environmental Group of the Year, Law 360, January 2018
  • 2021 and 2017 Chambers USA Environment Law Firm of the Year
  • Selected as a Super Lawyer for Environmental Law, California Super Lawyers magazine, 2014-2021