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lib/weather/extras/air-quality.ts

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+import { fetchJson, maybe } from "../http";
+import type { AirQuality } from "../types";
+
+/**
+ * Air quality from Open-Meteo's free air-quality API (CAMS data), used for
+ * every provider so the AQI always means the same thing.
+ * Docs: https://open-meteo.com/en/docs/air-quality-api
+ *
+ * The same call also tells us the location's IANA time zone, which some
+ * providers (Tomorrow.io, OpenWeather free) don't give us.
+ */
+
+interface AirQualityResponse {
+  timezone: string;
+  current: {
+    us_aqi: number | null;
+    pm2_5: number | null;
+    pm10: number | null;
+    ozone: number | null;
+    nitrogen_dioxide: number | null;
+  };
+}
+
+export interface LocalContext {
+  timeZone: string;
+  airQuality: AirQuality | null;
+}
+
+export async function getLocalContext(lat: number, lon: number): Promise<LocalContext> {
+  const params = new URLSearchParams({
+    latitude: String(lat),
+    longitude: String(lon),
+    current: "us_aqi,pm2_5,pm10,ozone,nitrogen_dioxide",
+    timezone: "auto",
+  });
+  const data = await fetchJson<AirQualityResponse>(
+    `https://air-quality-api.open-meteo.com/v1/air-quality?${params}`,
+    "Open-Meteo air quality",
+    { cacheSeconds: 1800 }, // air quality updates hourly at most
+  );
+
+  const c = data.current;
+  return {
+    timeZone: data.timezone,
+    airQuality:
+      c.us_aqi === null
+        ? null
+        : { usAqi: Math.round(c.us_aqi), pm25: maybe(c.pm2_5), pm10: maybe(c.pm10), ozone: maybe(c.ozone), no2: maybe(c.nitrogen_dioxide) },
+  };
+}