Estimation of the NO2 population exposure in the Northern Harbour district of Malta

Abstract

This study presents an estimate of the total NO2 exposure in a polluted and densely populated region in Malta, the Northern Harbour district. To estimate the population mobility, we follow a dynamic approach whereby four microenvironments are mapped onto defined Copernicus Urban Atlas 2012 land use classifications. These include the home (ME_home), work (ME_work), traffic (ME_traffic), and other outdoor activities (ME_other) microenvironments. In addition, generic time-activity profiles are used to estimate the hourly mobility in the different microenvironments depending on weekday or weekend profiles. Measured hourly NO2 ambient concentrations from the air quality network run by the Environment and Resources Authority (ERA) are used in conjunction with the estimated time-activity profiles to calculate the total exposure.

The highest NO2 population exposure is estimated for ME_home (71%) as people spend the majority of the time in this microenvironment followed by ME_other (15%), ME_work (10%) and ME_traffic (4%), respectively. In addition, we test the sensitivity of the total NO2 exposure to changes in NO2 concentrations for different microenvironments. The total NO2 exposure using infiltration rates to estimate infiltrated outdoor NO2 concentrations in indoor microenvironments, is up to 25% lower compared to the NO2 exposure estimated using outdoor NO2 concentrations for all microenvironments. Results also suggest a decrease of 3% in the estimated NO2 exposure if a static population is assumed for each microenvironment as opposed to a dynamic one. Exposure assessments such as that presented in this study are essential to aid the development of targeted policies to limit such exposures.