specification: API Commons Rate Limits
specificationVersion: '0.1'
schema: https://raw.githubusercontent.com/api-evangelist/interface-research/main/schema/api-commons.yml#/$defs/RateLimits
provider: U.S. Environmental Protection Agency
providerId: epa
created: '2026-05-29'
modified: '2026-05-29'
reconciled: true
tags:
  - Rate Limiting
  - Government
  - Environmental
description: >-
  The U.S. EPA operates several distinct API surfaces, each with its own
  rate-limiting regime. The Air Quality System (AQS) Data Mart caps clients at
  10 requests per minute with a recommended 5-second pause between calls and a
  per-query row ceiling. The Clean Air Markets (CAM) easey APIs enforce a
  per-key 1,000 requests/hour quota plus a 15-minute single-request timeout and
  500-row page maximum. The Envirofacts REST data service does not publish an
  explicit per-second cap but rejects queries that fail to complete within 15
  minutes. ECHO, FRS, ATTAINS, How's My Waterway, and most other open Envirofacts-
  fronted services are public and unauthenticated; reasonable use is expected.
  Several authenticated surfaces (Grants, FRS Submit, e-Manifest production)
  require credentials issued by EPA program offices and apply program-specific
  throttling.
sources:
  - https://aqs.epa.gov/aqsweb/documents/data_api.html
  - https://www.epa.gov/power-sector/cam-api-portal
  - https://www.epa.gov/enviro/envirofacts-data-service-api
  - https://www.epa.gov/data/application-programming-interface-api
  - https://echo.epa.gov/tools/web-services
  - https://www.epa.gov/frs/facility-registry-service-frs-api
responseCodes:
  throttled: 429
  quotaExceeded: 429
  requestTimeout: 408
  serviceUnavailable: 503
headers:
  retryAfter: Retry-After
  requestId: X-Request-Id
limits:
  - name: AQS Data Mart — request rate
    scope: account/key
    metric: requests_per_minute
    limit: 10
    timeFrame: minute
    notes: AQS documents a maximum of 10 requests per minute, with a 5-second recommended pause between requests; clients must await completion before submitting the next.
  - name: AQS Data Mart — interval between requests
    scope: account/key
    metric: seconds_between_requests
    limit: 5
    timeFrame: second
    notes: Minimum 5-second pause between successive requests.
  - name: AQS Data Mart — per-query row ceiling
    scope: query
    metric: rows_per_query
    limit: 1000000
    notes: Queries returning more than 1,000,000 rows are discouraged and may be terminated.
  - name: AQS Data Mart — parameter codes per request
    scope: query
    metric: parameters_per_request
    limit: 5
    notes: Maximum of 5 AQS parameter codes per request.
  - name: Clean Air Markets (easey) — request rate
    scope: account/key
    metric: requests_per_hour
    limit: 1000
    timeFrame: hour
    notes: Default per-key rate limit across all CAM streaming, emissions, facilities, accounts, and CAMD services.
  - name: Clean Air Markets (easey) — request timeout
    scope: request
    metric: minutes_per_request
    limit: 15
    timeFrame: minute
    notes: A single CAM API request will time out after 15 minutes.
  - name: Clean Air Markets (easey) — page size
    scope: query
    metric: rows_per_page
    limit: 500
    notes: Maximum 500 rows per page for paginated CAM endpoints.
  - name: Clean Air Markets (easey) — streaming UI download
    scope: request
    metric: rows_per_download
    limit: 1000000
    notes: 1,000,000 record maximum for streaming services UI downloads; programmatic API has no record cap.
  - name: Envirofacts Data Service — request timeout
    scope: request
    metric: minutes_per_request
    limit: 15
    timeFrame: minute
    notes: Envirofacts queries that fail to complete within 15 minutes are aborted; use pagination to stream large result sets.
  - name: ECHO Web Services — query ID lifetime
    scope: query
    metric: minutes_qid_valid
    limit: 30
    timeFrame: minute
    notes: ECHO get_facilities returns a query_id (QID) that is valid for roughly 30 minutes; subsequent get_qid / get_map / get_download calls must reference it within that window.
  - name: How's My Waterway, ATTAINS, FRS Query, e-Manifest, Insect Repellents, ELG Search
    scope: IP
    metric: varies
    limit: 'not publicly documented'
    notes: These public services do not publish a hard per-IP cap. Reasonable, well-behaved use is expected. Heavy scraping may be rate-limited at the edge by api.epa.gov or data.epa.gov.
policies:
  - name: ApiKeyRegistration
    description: AQS requires email-based registration that returns a key by email. CAM requires a key requested via the CAM API Portal. api.data.gov fronts other EPA APIs with its standard X-API-Key sign-up flow (1,000 requests/hour default).
  - name: ExponentialBackoff
    description: On 429 or timeout responses, retry with exponential backoff. The AQS docs recommend waiting for one request to complete before issuing the next; CAM recommends honoring Retry-After.
  - name: Pagination
    description: Envirofacts pages via path-segment ranges (`1:100`). CAM streaming and v2 endpoints page via offset/limit query parameters. Always page large extracts rather than relying on a single oversize query.
  - name: BulkDownloads
    description: For program-wide extracts, prefer the agency's bulk downloads (ECHO Exporter ZIPs, AQS pre-generated annual files, GHGRP downloads) over hammering the live APIs.
  - name: PrimacyAndStateData
    description: Several program APIs reflect data forwarded from state primacy agencies; freshness varies by program (AQS data can lag 6+ months from collection).
  - name: AuthenticatedSubmissions
    description: Submission APIs (FRS Submit, e-Manifest, Grants) are credentialed via NAAS/CDX and apply program-specific concurrency and throttling on a per-account basis.