fix: adopt 2024 EPA PM2.5 AQI breakpoints for cross-platform alignment

[jamesarich]

Why

Part of the cross-platform AQI alignment work (meshtastic/design#54). iOS is landing a computed EPA NowCast AQI (meshtastic/Meshtastic-Apple#2075) built on the current (2024) EPA PM2.5 24-hour breakpoint table. Android's already-merged implementation (#6102) used the legacy (pre-2024) table, so the same PM2.5 reading produced a different AQI per platform — exactly the divergence design#54 exists to prevent.

This lands the 2024 table on Android before the iOS feature ships, so the two never present diverging curves.

Fixes #6272.

🐛 Changes

Swapped the PM2.5 breakpoint constants in core/model/.../util/AirQualityIndex.kt from the legacy table to the current 2024 EPA table (AQS parameter 88101):

PM2.5 (µg/m³) legacy	AQI	→	PM2.5 (µg/m³) 2024	AQI
0.0–12.0	0–50	→	0.0–9.0	0–50
12.1–35.4	51–100	→	9.1–35.4	51–100
35.5–55.4	101–150	→	35.5–55.4	101–150
55.5–150.4	151–200	→	55.5–125.4	151–200
150.5–250.4	201–300	→	125.5–225.4	201–300
250.5–500.4	301–500	→	225.5–325.4	301–500

Constants only. The NowCast weighting (12h rolling window, 0.5 min weight factor) and the Equation-1 linear interpolation are untouched.

🛠️ Testing Performed

Updated AirQualityIndexTest breakpoint vectors to the 2024 table and re-derived the affected expected AQI values:

• Boundary vectors: 9.0→50, 9.1→51, 35.4→100, 35.5→101, 55.4→150, 55.5→151, 125.4→200, 125.5→201, 225.4→300, 225.5→301, 325.4→500.
• Added a design#54 regression vector: PM2.5 = 10 µg/m³ → 53 ("Moderate"), which was 42 ("Good") on the legacy table (matches the worked example in Update PM2.5 AQI breakpoints to current (2024) EPA table for cross-platform alignment #6272 and the iOS reference).

Verified locally: ./gradlew :core:model:allTests (all 11 AirQualityIndex tests pass), plus spotlessApply spotlessCheck detekt all clean.

Summary by CodeRabbit

• Bug Fixes

  • Updated PM2.5 air-quality calculations to use the EPA’s 2024 breakpoint values.
  • Improved AQI accuracy for low-to-mid PM2.5 concentrations, including a PM2.5 reading of 10 µg/m³ mapping to an AQI of 53.

• Tests

  • Added regression coverage to verify AQI results against the updated EPA guidance.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 69b835da-4662-4b81-9382-22ba0ec425fc

📥 Commits

Reviewing files that changed from the base of the PR and between 0c21e98 and 43f16c7.

📒 Files selected for processing (2)

• core/model/src/commonMain/kotlin/org/meshtastic/core/model/util/AirQualityIndex.kt
• core/model/src/commonTest/kotlin/org/meshtastic/core/model/util/AirQualityIndexTest.kt

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📝 Walkthrough

Walkthrough

The PM2.5 AQI breakpoint table now uses 2024 EPA concentration ranges. Existing breakpoint tests were updated, and a regression test verifies that 10.0 µg/m³ maps to AQI 53.

Changes

PM2.5 AQI breakpoint update

Layer / File(s)	Summary
Breakpoint table and validation core/model/src/commonMain/.../AirQualityIndex.kt, core/model/src/commonTest/.../AirQualityIndexTest.kt	The PM2.5 concentration ranges use the 2024 EPA table, with updated breakpoint assertions and a regression test for 10.0 µg/m³ → AQI 53.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related issues

• Meshtastic Apple issue 2040 — Both changes update PM2.5-to-AQI breakpoint calculations, and this PR applies the corresponding 2024 EPA table on Android.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adopting the 2024 EPA PM2.5 AQI breakpoints for cross-platform alignment.
Linked Issues check	✅ Passed	The breakpoint constants and tests were updated to the 2024 EPA table, matching the linked issue's requirements and preserving interpolation logic.
Out of Scope Changes check	✅ Passed	The PR stays focused on AQI breakpoint updates and test adjustments, with no unrelated code changes visible in the summary.

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