diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cf7b6363..442630c09 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -45,11 +45,13 @@ an earlier fold computed from part of a day.
   Location & weather (on by default), attributions beside the values, and a
   dashboard chip on a day with high pollen, a warm night or very poor air.
 - **Air quality for the past.** A background job fills air quality, pollen
-  and UV for every earlier local day with an entry: after the update, when
-  the home is set and when air quality is switched on. A trip day is fetched
-  at the trip's place, other days at the home, also before it was set. The
-  source reaches back to 2013 in Europe and to August 2022 elsewhere, pollen
-  from 2021 in Europe only; older days stay empty. Nearby days share one
+  and UV for earlier local days with an entry: after the update, when the
+  home is set and when air quality is switched on. A day inside a location
+  period is fetched at that place, a day from the home's effective date on
+  at the home; a day before it with no period stays empty rather than
+  borrowing a place the person was not at. The source reaches back to 2013
+  in Europe and to August 2022 elsewhere, pollen from 2021 in Europe only;
+  older days stay empty. Nearby days share one
   request of up to 90 days, a run holds itself to 300 of the account's 400
   daily calls and half of each instance window, and a long history spreads
   over several nights. Location & weather shows the progress (migration
diff --git a/src/lib/environment/__tests__/air-quality-history.test.ts b/src/lib/environment/__tests__/air-quality-history.test.ts
index 23d62f31a..4b58cccb4 100644
--- a/src/lib/environment/__tests__/air-quality-history.test.ts
+++ b/src/lib/environment/__tests__/air-quality-history.test.ts
@@ -135,13 +135,27 @@ describe("resolveHistoryLocation", () => {
     });
   });
 
-  it("places a day before the home was set at the home", () => {
-    expect(resolveHistoryLocation("2020-03-01", home, [trip])).toMatchObject({
+  it("places a day from the home's effective date on at the home", () => {
+    expect(resolveHistoryLocation("2026-09-01", home, [trip])).toMatchObject({
       lat: 51.5,
       source: "HOME",
     });
   });
 
+  it("leaves a day before the home was set without a place, unless a period covers it", () => {
+    expect(resolveHistoryLocation("2026-08-31", home, [trip])).toBeNull();
+    expect(resolveHistoryLocation("2020-03-01", home, [trip])).toBeNull();
+    expect(resolveHistoryLocation("2024-07-14", home, [trip])).toMatchObject({
+      source: "TRAVEL",
+    });
+  });
+
+  it("places every day at a home stored without an effective date", () => {
+    expect(
+      resolveHistoryLocation("2015-01-01", { ...home, since: null }, []),
+    ).toMatchObject({ lat: 51.5, source: "HOME" });
+  });
+
   it("places nothing without a home or a period", () => {
     expect(resolveHistoryLocation("2020-03-01", null, [trip])).toBeNull();
   });
diff --git a/src/lib/environment/air-quality-history.ts b/src/lib/environment/air-quality-history.ts
index 5b515a674..7d2ea80a2 100644
--- a/src/lib/environment/air-quality-history.ts
+++ b/src/lib/environment/air-quality-history.ts
@@ -15,13 +15,17 @@
  *     (only the air-quality part is fetched then, as the nightly gap fill
  *     does);
  *   - otherwise in the dated location period that covers it, else at the
- *     home. Unlike the nightly resolver this also places days before
- *     `homeSince` at the home: those are exactly the days the history is for,
- *     and a period entered for a trip still wins. Such a day gets its weather
- *     row with the air quality, because the air quality is stored on it.
+ *     home, but the home only from `homeSince` on (or on every day when no
+ *     `homeSince` is stored). A day before the home was set is never placed
+ *     there: the weather and air of a place the person was not at would be
+ *     wrong data in the correlations, the Coach and the day view, and an
+ *     empty day is honest where a wrong one is not. Such a day is filled
+ *     only when a period covers it. A day without a row gets its weather row
+ *     with the air quality, because the air quality is stored on it.
  *
  * A day inside a period whose sealed location does not open is skipped (fail
- * closed, as in the service), and so is a day with no place at all. A day the
+ * closed, as in the service), and so is a day with no place at all; neither
+ * counts towards the progress, which counts only days that can be filled. A day the
  * source does not reach at its location (before 2013 in Europe, before August
  * 2022 elsewhere, `earliestAirQualityDay`) is neither fetched nor counted: it
  * stays without a value, which says nothing about the air, rather than
@@ -189,7 +193,9 @@ export function historyRequestFits(
 
 /**
  * Where a day without a row is placed: the period that covers it, else the
- * home, also before `homeSince` (see the header). Pure; exported for tests.
+ * home from `homeSince` on, or on every day when no `homeSince` is stored
+ * (see the header). Null for a day before the home with no period. Pure;
+ * exported for tests.
  */
 export function resolveHistoryLocation(
   day: string,
@@ -201,7 +207,7 @@ export function resolveHistoryLocation(
       return { lat: t.lat, lon: t.lon, label: t.label, source: "TRAVEL" };
     }
   }
-  if (home) {
+  if (home && (home.since === null || day >= home.since)) {
     return { lat: home.lat, lon: home.lon, label: home.label, source: "HOME" };
   }
   return null;
diff --git a/tests/integration/environment-air-quality-history.test.ts b/tests/integration/environment-air-quality-history.test.ts
index ef377f916..b71bf55ae 100644
--- a/tests/integration/environment-air-quality-history.test.ts
+++ b/tests/integration/environment-air-quality-history.test.ts
@@ -4,7 +4,10 @@
  *
  *   - every past local day with an entry is filled: a day with a weather row
  *     gets its air quality, a day without one gets both, a day of a trip is
- *     fetched at the trip's place, a day before the home was set at the home;
+ *     fetched at the trip's place, a day from the home's effective date at
+ *     the home;
+ *   - a day before the home was set is filled only inside a location period;
+ *     without one it stays empty and is not counted;
  *   - a day before the source reaches stays without a row and is not counted,
  *     and the last week is left to the nightly fetch;
  *   - nearby days share one request, the coordinates sent are the coarse
@@ -32,6 +35,7 @@ const OWNER = "aq-history-owner";
 const NOW = new Date("2026-10-09T03:00:00Z");
 const BOCHUM = { lat: 51.5, lon: 7.2, label: "Bochum" };
 const LISBON = { lat: 38.7, lon: -9.1, label: "Lisbon" };
+const ESSEN = { lat: 51.5, lon: 7.0, label: "Essen" };
 
 function daysBetween(start: string, end: string): string[] {
   const out: string[] = [];
@@ -108,8 +112,8 @@ beforeEach(async () => {
       timezone: "Europe/Berlin",
       homeLocationEncrypted: sealLocation(BOCHUM),
       homeTimezone: "Europe/Berlin",
-      // Set recently: every day below lies before it.
-      homeSince: new Date("2026-09-01T00:00:00Z"),
+      // Days before it are filled only inside a location period.
+      homeSince: new Date("2025-01-01T00:00:00Z"),
       modulePreferencesJson: { environment: true },
     },
   });
@@ -121,16 +125,27 @@ beforeEach(async () => {
       locationEncrypted: sealLocation(LISBON),
     },
   });
-  // Entries: one before the source reaches, two nearby days in 2020, one on
-  // a trip, one on a day with a weather row lacking air quality, one on a
-  // day already done, a mood entry, and one inside the last week.
+  await prisma.environmentTravelLocation.create({
+    data: {
+      userId: OWNER,
+      startDate: "2020-03-01",
+      endDate: "2020-03-10",
+      locationEncrypted: sealLocation(ESSEN),
+    },
+  });
+  // Entries: one before the source reaches, two nearby days on a 2020 trip,
+  // one before the home with no trip, one on a 2024 trip, one on a day with a
+  // weather row lacking air quality, one on a day already done, one at home
+  // without a row, a mood entry, and one inside the last week.
   for (const day of [
     "2012-06-01",
     "2020-03-01",
     "2020-03-05",
+    "2020-06-01",
     "2024-07-05",
     "2025-05-01",
     "2025-06-01",
+    "2025-09-10",
     "2026-10-06",
   ]) {
     await measurementOn(day);
@@ -185,8 +200,8 @@ describe("air-quality history backfill", () => {
     const result = await runAirQualityHistory(OWNER, { now: NOW });
     expect(result).toMatchObject({
       status: "complete",
-      total: 5,
-      done: 5,
+      total: 6,
+      done: 6,
       remaining: 0,
     });
 
@@ -200,16 +215,29 @@ describe("air-quality history backfill", () => {
       "2024-07-05",
       "2025-05-01",
       "2025-06-01",
+      "2025-09-10",
     ]);
+    // Before the home and outside every period: no row, not counted.
+    expect(rows.find((r) => r.date === "2020-06-01")).toBeUndefined();
     for (const row of rows) expect(row.aqFetchedAt).not.toBeNull();
     const byDate = new Map(rows.map((r) => [r.date, r]));
-    // A day before the home was set: placed at the home, weather and air.
+    // A day before the home was set, inside a period: at the period's place.
     expect(byDate.get("2020-03-01")).toMatchObject({
-      source: "HOME",
+      source: "TRAVEL",
       pm25Mean: 12,
       tempMax: 5,
       lat: null,
     });
+    expect(
+      openLocation(byDate.get("2020-03-01")!.locationEncrypted!),
+    ).toMatchObject({ lat: 51.5, lon: 7.0 });
+    // A day after the home was set, without a row: at the home.
+    const home = byDate.get("2025-09-10")!;
+    expect(home).toMatchObject({ source: "HOME", pm25Mean: 12, tempMax: 5 });
+    expect(openLocation(home.locationEncrypted!)).toMatchObject({
+      lat: 51.5,
+      lon: 7.2,
+    });
     // Pollen is not asked for before 2021, so it stays null, not zero.
     expect(byDate.get("2020-03-01")!.pollenBirchMax).toBeNull();
     // A trip day: at the trip's place.
@@ -238,6 +266,7 @@ describe("air-quality history backfill", () => {
         u.searchParams.get("end_date"),
       ]),
     ).toEqual([
+      ["2025-09-10", "2025-09-10"],
       ["2025-05-01", "2025-05-01"],
       ["2024-07-05", "2024-07-05"],
       ["2020-03-01", "2020-03-05"],
@@ -254,12 +283,12 @@ describe("air-quality history backfill", () => {
       sent
         .filter((u) => u.pathname === "/v1/archive")
         .map((u) => u.searchParams.get("start_date")),
-    ).toEqual(["2024-07-05", "2020-03-01"]);
+    ).toEqual(["2025-09-10", "2024-07-05", "2020-03-01"]);
 
     const user = await prisma.user.findUniqueOrThrow({ where: { id: OWNER } });
     expect(user.environmentAqHistoryJson).toMatchObject({
-      total: 5,
-      done: 5,
+      total: 6,
+      done: 6,
       complete: true,
     });
 
@@ -284,7 +313,7 @@ describe("air-quality history backfill", () => {
     expect(fetchSpy).not.toHaveBeenCalled();
     const user = await prisma.user.findUniqueOrThrow({ where: { id: OWNER } });
     expect(user.environmentAqHistoryJson).toMatchObject({
-      total: 5,
+      total: 6,
       done: 1,
       complete: false,
     });