**Indoor Particle Concentrations, Size Distributions, and Exposures in Middle Eastern Microenvironments**

**Tareq Hussein 1,2,\*, Ali Alameer 1, Omar Jaghbeir 1, Kolthoum Albeitshaweesh 1, Mazen Malkawi 3, Brandon E. Boor 4,5, Antti Joonas Koivisto 2, Jakob Löndahl 6, Osama Alrifai <sup>7</sup> and Afnan Al-Hunaiti <sup>8</sup>**


Received: 11 November 2019; Accepted: 25 December 2019; Published: 28 December 2019

**Abstract:** There is limited research on indoor air quality in theMiddle East. In this study, concentrations and size distributions of indoor particles were measured in eight Jordanian dwellings during the winter and summer. Supplemental measurements of selected gaseous pollutants were also conducted. Indoor cooking, heating via the combustion of natural gas and kerosene, and tobacco/shisha smoking were associated with significant increases in the concentrations of ultrafine, fine, and coarse particles. Particle number (PN) and particle mass (PM) size distributions varied with the different indoor emission sources and among the eight dwellings. Natural gas cooking and natural gas or kerosene heaters were associated with PN concentrations on the order of 100,000 to 400,000 cm−<sup>3</sup> and PM2.5 concentrations often in the range of 10 to 150 μg/m3. Tobacco and shisha (waterpipe or hookah) smoking, the latter of which is common in Jordan, were found to be strong emitters of indoor ultrafine and fine particles in the dwellings. Non-combustion cooking activities emitted comparably less PN and PM2.5. Indoor cooking and combustion processes were also found to increase concentrations of carbon monoxide, nitrogen dioxide, and volatile organic compounds. In general, concentrations of indoor particles were lower during the summer compared to the winter. In the absence of indoor activities, indoor PN and PM2.5 concentrations were generally below 10,000 cm−<sup>3</sup> and 30 μg/m3, respectively. Collectively, the results suggest that Jordanian indoor environments can be heavily polluted when compared to the surrounding outdoor atmosphere primarily due to the ubiquity of indoor combustion associated with cooking, heating, and smoking.

**Keywords:** indoor air quality; aerosols; particle size distributions; ultrafine particles; particulate matter (PM); smoking; combustion
