Contributions of Indoor and Outdoor Sources to Ozone in Residential Buildings in Nanjing

Abstract

Ozone has become one of the most serious air pollutants in China in recent years. Since people spend most of their time indoors, the ozone in the indoor environment could be a major factor affecting the occupants’ health. The indoor ozone in residential buildings mainly comes from two sources: outdoor atmosphere and indoor ozone produced by electrical devices. In this study, a typical residence in Nanjing was taken as an example to calculate and compare the contributions of indoor and outdoor sources to ozone in the building. A questionnaire survey about the type, the placement, and the frequency of use of the ozone emission devices was performed to provide the basis for the settings of indoor ozone sources. The multi-zone software CONTAM was used hourly to simulate the ozone concentration in summer and in winter with inner doors either closed or open, and it was noted whether there were ozone emission devices indoors or not. Source contribution was quantified and compared by three methods in this paper: (1) the average indoor/outdoor (I/O) ratio, (2) the I/O ratio frequency, and (3) the ratio of indoor ozone concentration without ozone sources to that with ozone sources. The results showed that the contribution of outdoor sources was much greater than that of indoor sources in summer, but in winter, the frequency of I/O > 1 could reach 55.8% of the total seasonal time, and the ratio of indoor ozone concentration without sources to that with sources could reach as high as 74.3%. This meant that the indoor concentration had the potential to exceed the outdoor. Furthermore, human respiratory exposure in different ages and genders was calculated. It was found that teenagers aged 10–18 years old and female adults had a higher respiratory exposure level.

Indoor Air Pollution, Related Human Diseases, and Recent Trends in the Control and Improvement of Indoor Air Quality

“…Ozone enables rapid reaction with several indoor pollutants, but the reaction products can irritate humans and damage materials. The main sources of indoor ozone mainly come from the outdoor atmosphere and the operation of electrical devices [52]. The machines commonly emitting indoor ozone gas include photocopiers, disinfecting devices, air-purifying devices, and other office devices [53][54][55][56].…”

Air pollution and indoor settings

“…The commonly used indoor ozone emission devices include photocopyiers, room air purifiers, disinfecting devices, and laser printers. 6 In a study, indoor ozone concentration fluctuated between 20% and 80% of the outdoor ozone concentration depending on the air exchange rate. 7 …”

“…Air pollution has been strongly associated with an increased risk of mortality from cardiovascular disease, myocardial infarction, stroke, and hospitalization for congestive heart failure and hypertension. 54 , 6 Mild increases in carboxyhemoglobin levels (by 3%–6%) occur when individuals are exposed to traffic pollution, and they can trigger angina and arrhythmias in individuals with coronary heart disease. 55 Long-term exposure increases the risk of cardiovascular mortality and reduces life expectancy in more exposed segments of the population from several months to a few years.…”

Ultrafine particle emission from floor cleaning products

“…The outdoor O 3 concentrations also resulted quite constant during the measurement periods (average value 117 µg/m 3 , standard deviation 15.1 µg/m 3 ). As mentioned above, even if indoor O 3 concentrations were not measured, the outdoor value can provide a good estimate of the indoor values when no indoor sources are present (as in the room where the tests were performed) and indoor‐to‐outdoor concentration ratio is increased opening the windows 32,43 …”

“…Indeed, even if the physical‐chemical process involving the indoor formation of SOA is well known, 11,13,19 as well as the effect of the main influencing parameters, 42 no studies were performed to quantify the emission of the SOA indoor sources. This is even more important for number‐based aerosol metrics, because the contribution of very small particles formed via nucleation on mass‐based aerosol metrics, that is, PM fractions, is expected to be negligible; as an example, the SOA contribution in indoor environments in terms of PM 2.5 was detected as low as <3% 43 . Moreover, most of the studies investigating the indoor generation of SOAs from VOC‐ozone interaction were performed in controlled chamber under meteo‐climatic conditions and ozone concentrations reproduced ad hoc in order to emphasize the nucleation phenomena but that could differ from the actual indoor environment conditions and the actual use of household cleaning products 9,44,45 …”