PM2.5 concentration from bus traffic in Helsinki in 2020

Scope

• Spatial limits: Helsinki metropolitan area
• Temporal limits: year 2020
• Type of pollutant: primary PM2.5
• Source of pollutant: bus traffic

Definition

Causality

List of parents:

• Variable:PM2.5 emissions from bus traffic

Data

List of data files or sources:

• Database from EXPOLIS study (1996-1997) - individual measurements of total outdoor PM exposure
• Database from ULTRA study - fixed monitoring sites

Formula

Total PM2.5 exposure/concentration was used as the starting point for the calculations of PM2.5 due to bus traffic, subtracting the contributions from other sources.

E_bus = (E_c-E_lrt)/f_tr*f_bus

fi = (Em_i * wf_i)/Sum(Em_i*wf_i)

Where:

E_bus is average PM2.5 exposure to primary particles from local buses
E_c is exposure to total exposure to combustion originating particles
E_lrt is the concentration of combustion-based long-range transport (average exposure to long-range transported PM2.5)
f_tr is the ratio of local road traffic exposure to local CoPM
f_bus is the ratio of local bus-derived primary CoPM to all local road-traffic-derived CoPM
Em_i is the CoPM emissions in the Helsinki area (tn/year)
wf_i is the relative weight factors to CoPM-emissions
Index i denotes different CoPM sources in Helsinki
wf is an estimate of the the impact of a unit emission on the average population exposure in the area

Unit

μg/m³

Result

Estimation of average bus-related primary PM2.5 in 2020 in Helsinki area