# S4-L2-NO2

## Variables

The table below lists the variables that are present in the HARP product that results from an ingestion of `S4-L2-NO2` data.

field name | type | dimensions | unit | description
--- | --- | --- | --- | ---
datetime | double | {time} | [seconds since 2000-01-01] | time of the measurement
datetime_length | double |  | [s] | measurement duration
latitude | float | {time} | [degree_north] | pixel center latitude
longitude | float | {time} | [degree_east] | pixel center longitude
latitude_bounds | float | {time, 4} | [degree_north] | latitudes of pixel boundary
longitude_bounds | float | {time, 4} | [degree_north] | latitudes of pixel boundary
validity | int8 | {time} |  | continuous quality descriptor, varying between 0 (no data) and 100 (full quality data)
NO2_column_number_density | float | {time} | [mol/m2] | mole content of nitrogen dioxide
NO2_column_number_density_uncertainty | float | {time} | [mol/m2] | standard error of mole content of nitrogen dioxide
stratospheric_NO2_column_number_density | float | {time} | [mol/m2] | troposphere mole content of nitrogen dioxide
stratospheric_NO2_column_number_density_amf | float | {time} | [] | stratospheric air mass factor
tropospheric_NO2_column_number_density | float | {time} | [mol/m2] | troposphere mole content of nitrogen dioxide
tropospheric_NO2_column_number_density_uncertainty | float | {time} | [mol/m2] | standard error of troposphere mole content of nitrogen dioxide
tropospheric_NO2_column_number_density_amf | float | {time} | [] | tropospheric air mass factor
index | int32 | {time} |  | zero-based index of the sample within the source product

## Ingestion options

The table below lists the available ingestion options for `S4-L2-NO2` products.

option name | legal values | description
--- | --- | ---
total_column | summed, total | whether to use nitrogen_dioxide_doas_total_column (which is derived from the total slant column divided by the total amf) or nitrogen_dioxide_summed_total_column (which is the sum of the retrieved tropospheric and stratospheric columns); option values are ‘summed’ (default) and ‘total’

## Mapping description

The table below details where and how each variable was retrieved from the input product.

field name | mapping description
--- | ---
datetime | path | /@time_reference_days_since_1950, /PRODUCT/delta_time[]
description | time reference converted from days since 1950-01-01 to seconds since 2020-01-01 (using 86400 seconds per day) and delta_time added
datetime_length | path | /PRODUCT/delta_time[]
description | delta_time[num_ground_pixels] - delta_time[0]
latitude | path | /PRODUCT/latitude[]
longitude | path | /PRODUCT/longitude[]
latitude_bounds | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/latitude_bounds[]
longitude_bounds | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/longitude_bounds[]
validity | path | /PRODUCT/qa_value
NO2_column_number_density | condition | total_column=summed or total_column unset
path | /PRODUCT/nitrogen_dioxide_summed_total_column[]
condition | total_column=total
path | /PRODUCT/nitrogen_dioxide_doas_total_column[]
NO2_column_number_density_uncertainty | available | optional
condition | total_column=total
path | /PRODUCT/nitrogen_dioxide_doas_total_column_precision[]
stratospheric_NO2_column_number_density | path | /PRODUCT/nitrogen_dioxide_stratospheric_column[]
stratospheric_NO2_column_number_density_amf | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/nitrogen_dioxide_stratospheric_air_mass_factor[]
tropospheric_NO2_column_number_density | path | /PRODUCT/nitrogen_dioxide_tropospheric_column[]
tropospheric_NO2_column_number_density_uncertainty | path | /PRODUCT/nitrogen_dioxide_tropospheric_column_precision[]
tropospheric_NO2_column_number_density_amf | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/nitrogen_dioxide_tropospheric_air_mass_factor[]