| Location | Site | Condition | Concentration Mean ± SD (range) (ppm) | Duration | Referee |
| Canada | Highway | 0.023 ± 0.002 (0.012 - 0.029) | 1 week | [49] | |
| Bahrain | Urban | 0.019 ± 0.007 (0.007 - 0.040) | 1 week | [56] | |
| Hertfordshire and North London | Gas Cooker | Personal Exposure (Winter) Personal Exposure (Summer) | 0.011 ± 0.002 (0.006 - 0.015) 0.015 ± 0.002 (0.001 - 0.002) | 1 week | [31] |
| Electric Cookers | Personal Exposure (Winter) Personal Exposure (Summer) | 0.008 ± 0.002 (0.006 - 0.011) 0.013 ± 0.001 (0.001 - 0.015) | |||
| Hong Kong | Resident and Office | Personal Exposure | 0.024 ± 0.006 (0.014 - 0.039) | 1 week | [55] |
| North, California | School Site | Road Traffic | 0.021 ± 0.007 (0.001 - 0.037) | 1 week | [20] |
| Sao-Paulo, Brazil | Street, Road and Avenues | Heavy Traffic Light Traffic | 0.034 ± (0.031 - 0.036) 0.026 ± (0.023 - 0.028) | 1 week | [21] |
| El Paso, Texas | CAMS 6 (Highway) CAMS 41 (Chamizal National Memorial) | High Traffic Area | 0.021 ± 0.00 (0.016 - 0.023) 0.016 ± 0.001 (0.017 - 0.018) | 1 week | [54] |
| AL-Ain City, Abu Dhabi | Industrial Traffic Residential |
| 0.022 ± 0.004 (0.005 - 0.029) 0.032 ± 0.007 (0.023 - 0.043) 0.019 ± 0.004 (0.014 - 0.028) | 2 × 1 week | [53] |
| Wahga Town, Pakistan | Heavy Traffic, Populated Area | Outdoor | 0.015 ± 0.005 (0.011 - 0.021) | 1 week | [60] |
| Malaysia | Putra Makhota Toll Kajang Toll Sungai Besi Toll | Toll Plaza (Indoor) | 0.056 ± 0.014 (0.025 - 0.068) 0.087 ± 0.029 (0.033 - 0.133) 0.102 ± 0.047 (0.029 - 0.205) | 4 × 1 week | Current Study |
| Putra Makhota Toll Kajang Toll Sungai Besi Toll | Toll Plaza (Outdoor) | 0.041 ± 0.011 (0.031 - 0.066) 0.054 ± 0.011 (0.041 - 0.149) 0.095 ± 0.047 (0.057 - 0.181) |