Chemical speciation of PM2.5 in Tehran: Quantification of dust contribution and model validation

Özet

Each year, considerable levels of dust particles coming from arid regions of the earth contribute to the atmosphere. Because dust has serious environmental and human health effects, predictions of dust concentrations andtheir contribution to PM surface concentrations are essential for atmospheric research and the implementation ofair quality programs and rules. This study aims to assess dust contributions to PM2.5 in Tehran in order toprovide guidance for air quality management systems as well as validate the updated Dust Regional AtmosphericModel version 2 (BSC-DREAM8b) and the NMMB/BSC-Dust model using chemical speciation of ground-basedmeasurements of PM2.5. Accurate and reliable measurements are necessary to determine the sources of pollutants as well as to confirm, validate, and improve models. For this purpose, dust concentration and contributionwere calculated from chemical speciation of PM2.5 samples that were obtained on a 6 day basis for a whole yearfrom February 2014 to February 2015. The comparison of the dust observations to the model products revealedthat model outputs were in good agreement for the monthly averaged values. However, for the daily averagedvalues, models and ground observation showed a considerable difference. In order to understand possible reasons for the discrepancy, differences between neighboring grid cells were investigated, as well as the effect ofsampling frequency. It is found that agreement between models and observations was sensitive to samplingduration and frequency but not to spatial variability between grid cells. This study is the first validation of modeloutputs with the calculated dust concentration from ground-based chemical speciation of PM2.5 rather thanusing total PM or aerosol optical depth measurements as a proxy for dust concentrations.