Get hourly wildfire smoke concentrations from the HRRR-Smoke model

Retrieves hourly near-surface wildfire smoke concentrations (micrograms per cubic meter) from NOAA's High-Resolution Rapid Refresh (HRRR) model, cropped to an area of interest, and returns them as a single multi-layer raster (one layer per hour).

Usage

get_hrrr_smoke(
  geometries,
  start_date,
  end_date = start_date,
  variable = c("surface", "column"),
  hours = 0:23
)

Arguments

geometries: An sf-formatted dataframe (or an sfc geometry column) defining the area of interest, in any defined coordinate reference system. The returned raster is cropped to this area's bounding box.
start_date: The first day to retrieve, as a Date or a "YYYY-MM-DD" string.
end_date: The last day to retrieve (inclusive), as a Date or a "YYYY-MM-DD" string. Defaults to start_date. HRRR-Smoke is archived from 2021 onward; the most recent hours may not yet be posted.
variable: Which smoke quantity to retrieve: "surface" (default; near-surface concentration) or "column" (vertically integrated smoke). See Details.
hours: Which hours of each day (UTC, 0-23) to retrieve. Defaults to all 24; for lighter-temporal-weight coverage, pass e.g. seq(0, 21, by = 3).

Value

A terra::SpatRaster with one layer per successfully retrieved hour, cropped to the bounding box of geometries (buffered by one 3-kilometer cell). Hours missing from the archive are dropped with a single summary warning. The raster's components:

cell values: Numeric. The smoke quantity selected by variable: near-surface smoke concentration in micrograms per cubic meter (ug/m^3) when variable = "surface", or vertically integrated column smoke in milligrams per square meter (mg/m^2) when variable = "column".
layers: One layer per hour, in chronological order. Convert to a one-row-per-cell-per-hour tibble with terra::as.data.frame(x, xy = TRUE, wide = FALSE).
layer names: Character. The layer's timestamp in UTC, formatted "YYYY-MM-DD HH:00" (e.g. "2025-08-01 12:00").
time: POSIXct. The same UTC timestamps, retrievable with terra::time(); used directly by tidyterra and terra::animate().
coordinate reference system: The HRRR model's native projection (Lambert conformal conic), with 3-kilometer cells. Reproject with terra::project(), or transform vector layers to it with sf::st_transform(x, sf::st_crs(raster)) before mapping.

Details

HRRR is NOAA's 3-kilometer, hourly-updating weather model for the conterminous United States. Since late 2020 it has carried smoke as a modeled quantity, driven by satellite detections of active fires. This function returns the "analysis" field for each requested hour – the model's real-time estimate for the hour it was issued. Data are downloaded on demand from NOAA's free public archive. A two-week window at hourly resolution takes roughly a few minutes.

Two smoke quantities are available via variable:

"surface": Smoke mass density 8 meters above ground, in micrograms per cubic meter (ug/m^3). This approximates what people at ground level are breathing and is directly comparable to PM2.5 air quality readings, which use the same unit. For reference, the EPA's 24-hour PM2.5 standard is 35 ug/m^3.
"column": Vertically integrated smoke – all smoke in the atmospheric column above each cell – in milligrams per square meter (mg/m^2). This corresponds to what satellites see and includes high-altitude smoke that may never reach the ground.

Because HRRR covers only the conterminous United States, Alaska, Hawaii, and the territories are unsupported. Note also that these are model estimates, not directly-measure smoke concentration observations.

Examples

if (FALSE) { # \dontrun{
county = tigris::counties(state = "CA", cb = TRUE) %>%
  dplyr::filter(NAME == "Butte")

smoke = get_hrrr_smoke(
  geometries = county,
  start_date = "2025-07-20",
  end_date = "2025-08-03")

# quick look at one hour, and a simple animation across all hours
terra::plot(smoke[[1]])
terra::animate(smoke, pause = 0.1)
} # }