# Data dictionary

The main table contains exactly 100,000,000 rows at the grain **synthetic station × hourly timestamp**.

| Field | Type | Unit / meaning |
|---|---|---|
| `timestamp` | timestamp | Asia/Kolkata in Parquet export; stored internally as UTC epoch seconds |
| `station_id` | uint16 | Synthetic site identifier, joins to `stations.parquet` |
| `temperature_c` | float32 | °C |
| `relative_humidity_pct` | float32 | % |
| `wind_speed_ms` | float32 | m/s |
| `rainfall_mm` | float32 | mm/hour |
| `pm25_ugm3` | float32 | µg/m³ |
| `pm10_ugm3` | float32 | µg/m³ |
| `no2_ugm3` | float32 | µg/m³ |
| `co_mgm3` | float32 | mg/m³ |
| `so2_ugm3` | float32 | µg/m³ |
| `o3_ugm3` | float32 | µg/m³ |
| `event_code` | uint8 | 0 normal, 1 Diwali stress window, 2 lockdown regime, 3 cyclone regime, 4 heatwave state |
| `obs_mask` | uint16 bit mask | Per-variable observation mask; value is null when its bit is 0 |
| `split_code` | uint8 | 0 train, 1 validation, 2 test |

## `obs_mask` bits

Bit order is fixed and reproducible:

| Bit | Variable |
|---:|---|
| 0 | temperature_c |
| 1 | relative_humidity_pct |
| 2 | wind_speed_ms |
| 3 | rainfall_mm |
| 4 | pm25_ugm3 |
| 5 | pm10_ugm3 |
| 6 | no2_ugm3 |
| 7 | co_mgm3 |
| 8 | so2_ugm3 |
| 9 | o3_ugm3 |

`1` means observed and `0` means unavailable. Missingness occurs in clustered runs and differs by variable and station.

## Metadata tables

`stations.parquet` / `stations.csv` contains 1,000 explicitly synthetic sites. Coordinates are synthetic points around Kolkata and are **not official CPCB/WBPCB station coordinates**.

`spatial_graph_knn10.parquet` / `spatial_graph_knn10.csv` contains a directed 10-nearest-neighbor Haversine graph with distance and a Gaussian distance weight.