COVID lockdown pollution calculator

Negative vehicle-kilometers and a negative emission factor are rejected as invalid_input because a physical inventory cannot start from a negative distance or a negative grams-per-kilometer intensity.

What a lockdown pollution inventory is and how avoided mass is computed

The identity is the same one used in COVID mobility papers that convert a traffic shock into a mass: reduced vehicle-kilometers equal baseline_vkm minus lockdown_vkm, and avoided_mass_g equals that difference times emission_factor_g_per_km. If lockdown traffic exceeds the baseline the difference is negative and the endpoint reports an increase rather than inventing a floor at zero, because a honest inventory must be able to show a rebound. The calculator does not invent a fleet factor from a city name, does not call a traffic API, and does not apply a chemical transport model; those layers sit outside this multiply and should be applied in your own study if you need ambient concentrations rather than avoided mass at the tailpipe.

Input contract, aliases, negatives, and the mass you get back

Zero is valid on every factor. Example: ten million baseline vehicle-kilometers, four million lockdown vehicle-kilometers, and 0.32 grams per kilometer yield a sixty percent reduction and 1 920 000 grams avoided. POST a JSON body with three required finite numbers: baseline_vkm, the vehicle-kilometers traveled in the comparison or pre-lockdown period; lockdown_vkm, the vehicle-kilometers traveled during the lockdown window of the same length; and emission_factor_g_per_km, the fleet-average grams of pollutant per vehicle-kilometer. Accepted aliases for the baseline are baseline_vkt, vkm_baseline, vehicle_km_baseline, and baseline_vehicle_km. Accepted aliases for the lockdown total are lockdown_vkt, vkm_lockdown, vehicle_km_lockdown, and lockdown_vehicle_km. Accepted aliases for the factor are ef_g_per_km, emission_factor, g_per_km, factor_g_km, and ef. Each field may arrive as a JSON number or as a decimal numeric string. Missing fields, empty strings, non-finite values, and magnitudes beyond the supported absolute ceiling fail with invalid_input naming the field. A negative baseline, a negative lockdown total, or a negative emission factor is rejected because vehicle-kilometers and grams per kilometer cannot be negative; the error message states that the field cannot be negative and the request is not billed. On success the body echoes the cleaned inputs and returns reduced_vkm, avoided_mass_g as the primary mass, plus avoided_mass_kg, avoided_mass_t, and avoided_mass_lb, a direction of avoided, increased, or unchanged, and formula and equation strings for display. When the baseline is positive it also returns reduction_percent.

Where a COVID lockdown pollution calculator earns its keep

City air-quality desks use a COVID lockdown pollution calculator so a published drop in vehicle-kilometers times a fleet NOx or PM2.5 factor becomes a tonnes total they can drop into a briefing without opening a workbook of unit conversions. Failed validation does not consume balance. Keep requests small, pin the rounded gram, kilogram, tonne, and pound figures in tests, and you get reproducible avoided-mass estimates for homework, LMS plugins, sustainability scripts, and edge workers without standing up an emissions-inventory stack of your own. Academic groups that replicate 2020 mobility papers need a deterministic oracle that rejects a negative kilometer total as invalid_input instead of returning a hollow success with a negative distance that a buggy pipeline might treat as a credit. Classroom environmental-science labs and journalism desks often convert a stay-at-home traffic chart into a grams figure before they load a chemical transport model; calling a tiny parse API avoids pulling a desktop spreadsheet for a three-factor inventory.