Aerosols are tiny liquid and solid suspended particles that play an important role in the air quality and human health. Aerosol optical depth (AOD) is a measure of the amount of particles present in the vertical column of the Earth's atmosphere. Angstrom exponent (AE) is a qualitative measure of the dimensions of the dominant aerosols’ sizes. An investigation of the dusty day of May 9, 2021, in the Yazd city with a Calitoo hand-held sun-photometer measures the AOD between 0.98 and 1.42 and the AE very close to zero. The AOD of MODIS-Terra and that of MODIS-Aqua is above 0.90. Horizontal visibility has decreased to 3200 meters and the concentration of PM10 and PM2.5 has reached 4.6 times and 2.6 times of the maximum allowable value per day, respectively. The results of the HYSPLIT backward trajectory model introduce the main source of dust transfer to the Yazd atmosphere from the Iraq.