# Jerusalem Air Quality — Weekday vs Friday vs Shabbat (preliminary)

12 months of 5-minute resolution data (2025-04-28 → 2026-04-28) for 12 active
Israeli MoEP / Envista ARM stations in Jerusalem, pulled from
`https://air-papi.sviva.gov.il/v1/envista/...` (see
`research/api-air-sviva-gov-il.md`).

Daytime window = 07:00–22:00 local (Asia/Jerusalem). Friday evening through
Saturday morning is collapsed into "Sat" since Shabbat-observant traffic is
already off the road by then; this slightly understates the true Shabbat drop
because it includes Friday morning rush in "Fri".

Each station has ~50 Fridays and ~50 Saturdays in the window (station 623
joined Aug 2025, station 635 joined Feb 2026 — small samples flagged).

## Signal: traffic-derived gases drop sharply on Shabbat

Median Shabbat % drop vs Sun-Thu daytime mean, across the 12 stations:

| Pollutant | Friday % drop | Shabbat % drop |
|---|---|---|
| NO    | ~40 % | ~55 % |
| NOx   | ~34 % | ~52 % |
| NO₂   | ~30 % | ~47 % |
| Toluene | ~44 % | ~38 % |
| Benzene | ~25 % | ~21 % |
| CO    | ~7 %  | ~8 %  |

The signal is consistent, monotonic (Sun-Thu > Fri > Sat for every gaseous
traffic pollutant at every station except a couple of edge cases), and
strongest in the most observant neighbourhoods.

## Where the drop is biggest

Top stations by NOx Shabbat drop:

| Station ID | Location | NOx weekday | NOx Shabbat | % drop |
|---|---|---|---|---|
| 635 | Bezalel St (city centre, near Geula) | 34.0 | 9.0 | **73 %** |
| 310 | Central Bus Station Platform 10 | 130.0 | 40.5 | **69 %** |
| 458 | Devorah HaNevia St (residential) | 39.6 | 15.5 | **61 %** |
| 328 | Atarot industrial zone | 38.8 | 15.8 | **59 %** |
| 547 | Highway 16 / Beit interchange | 18.1 | 7.8 | **57 %** |
| 5   | Bar Ilan St (arterial) | 26.4 | 11.9 | **55 %** |
| 193 | Romema (ultra-Orthodox) | 14.3 | 6.8 | **52 %** |
| 607 | Beit Safafa | 18.6 | 9.3 | **50 %** |
| 13  | Baka (residential mixed) | 13.9 | 8.5 | **39 %** |
| 36  | Safra Square (city centre) | 11.1 | 7.5 | **33 %** |
| 623 | Atarot Eden (8 mo. only) | 12.1 | 9.1 | **25 %** |
| 568 | Rockefeller Museum | 33.1 | 28.7 | **13 %** |

Rockefeller Museum (568) is the surprise outlier — much smaller drop than
neighbours. Worth checking whether the inlet sits next to a road that
remains busy on Shabbat (Sultan Suleiman / Salah a-Din area carries a lot
of East-Jerusalem traffic, which doesn't observe Shabbat).

Conversely, the very tight grouping at 50–70 % drops in West-Jerusalem
arterial / residential stations is a strong correlate of the population's
observance of vehicular Shabbat.

## Friday is genuinely intermediate

Friday daytime sits roughly **half-way** between weekday and Shabbat for
NOx at most stations — consistent with reduced commercial activity but
ongoing pre-Shabbat shopping/errands until early afternoon.
`scripts/shabbat_correlation.py` also writes `station-{id}-friday-split.csv`
breaking Friday into AM (07–13) and PM (14–22) — the AM block looks like a
near-normal weekday; the drop concentrates in PM.

## PM2.5 / PM10 do **not** drop on Shabbat — they often rise

Particulate matter increases on Saturdays at almost every station (-30 % to
-65 % "drops", i.e. Sat is *higher* than weekday). Several plausible
contributors, none ruled out yet:

- April–May 2026 included multiple Saharan dust intrusions; 12 months is
  not enough to wash that out and Saturdays happened to coincide with some
  of them.
- Charcoal grilling (mangal) is a well-documented Israeli Friday-afternoon
  / Saturday source of PM2.5 and PM10.
- Reduced wind / different boundary-layer dynamics on weekends.

This is a real finding for the project but it cuts the other way from the
gaseous traffic story and deserves its own analysis (probably needs to
controlling for synoptic dust days).

## Caveats

- Daytime defined as 07–22 ignores the actual Shabbat onset/conclusion
  times, which vary 17:00–19:00 by season. A Hebcal-driven exact window
  would tighten the signal.
- Calendar holidays (Pesach 2025-04, Shavuot, Rosh Hashana, Yom Kippur,
  Sukkot, Hanukkah) are not excluded — Yom Kippur in particular is the
  cleanest air day of the year nationwide and inflates "weekday" cleanness
  for any year that includes it (Wed 2025-10-01 was YK 2025).
- 12 months × 5-min data is ~700k rows per station, ~2 GB total raw JSON;
  the raw is gitignored and regenerable via the API; only summary CSVs are
  committed.

## How to reproduce

```bash
# 1. Pull raw data (mints Guest tokens, ~2 GB)
.venv/bin/python -m pip install pandas numpy   # one-off
bash scripts/fetch_historical.sh               # (TODO: lift the inline pull from session)

# 2. Run analysis
.venv/bin/python scripts/shabbat_correlation.py
# → writes analysis/headline-3way.csv + per-station CSVs
```