The indoor air quality has a direct impact on human health. Particulate matter is one of the important factors affecting the indoor air quality. The paper selects an office as the study object and studies the pollution characteristics and dynamic changes of indoor particulate matter in different outdoor pollution levels. The mass concentration of outdoor PM10 is used as the evaluation basis of the outdoor pollution level. The outdoor PM10 concentration levels are divided into the range of 200–300, 300–400, 400–500, 500–600, 600–700
With the rapid development of economy and the continuous improvement of living standards, people’s requirements for indoor environment are not only confined to indoor thermal comfort but also placed on the indoor particle pollution, namely, indoor air quality. According to the relevant data, a majority of people spend 70∼90% of their time indoors, especially for the elderly people and the disabled man [
Particulate matter is one of the primary pollutants in indoor pollution [
Researches on the relationship between indoor and outdoor particulate matter concentrations show that the mass concentration of the particles entering the indoor environment is in the same order of magnitude as the mass concentration of the outdoor atmospheric particles [
This paper takes an office in north China as the research object. Outdoor infiltration experiment and correlation experiment are conducted. The experiment measures the changes of mass concentration and particle number concentration of indoor particulate matter in various conditions. Then, the pollution characteristics and dynamic changes of indoor particulate matter under different particulate concentrations are studied. The maximum increase values, the maximum increase rates, and the penetration factors are calculated and compared. Finally, the correlation between indoor particulate matter and outdoor particulate matter is studied.
The experimental subject is an office on the third floor in a university office building in Baoding.
The office building is 100 m away from the trunk road in urban areas. The area of the office is 38.8 m2 (7.6 m × 5.1 m), the door is 1.8 m2 (0.9 m × 2.0 m), and the window is 4.2 m2 (1.2 m × 0.87 m × 4); the floor is covered by the ordinary cement mortar. The landscape of the building is shown in Figure
(a) The landscape of the building and (b) the layout of the experiment office.
According to the diagonal principle, the sampling point in the experiment was set in the center of the room. And it was set at 0.8 m above the floor level [
Measurement parameters and measuring instruments.
Parameters | Instrument | Model | Range | Accuracy |
---|---|---|---|---|
Mass concentration | Intelligent dust detector | DUSTTRAK 8520 | 0.001–100 mg·m−3 | ±0.001 mg·m−3 |
Number concentration | Laser particle counter | AEROTRAK 8220 | >0.3 |
±5% |
There are three ways for outdoor pollutants to enter the room: air infiltration via gaps of doors and windows, natural ventilation, and personnel entering. This study only considers air infiltration, and the door and windows were closed when the experiment was carried out. Thus, the outdoor pollution source entered the room through air infiltration. The outdoor wind condition is an important factor affecting the air infiltration. To ensure the unity of the experimental conditions, the experiment was conducted in sunny days and the windless or breezy days; that is, the influence of the wind condition on the experiment was neglected.
In the experiment, the mass concentration of PM10 of the outdoor atmosphere was used as the evaluation basis of the outdoor pollution level. The outdoor pollution levels were divided into 200–300, 300–400, 400–500, 500–600, and 600–700
As the experiment duration is only two hours and the experiment was conducted in sunny days and the windless or breezy days, the outdoor PM10 mass concentration did not greatly change during the experiment duration (two hours). During the experiment of a certain condition of outdoor PM10 concentration, the outdoor PM10 concentration was also measured, and the outdoor PM10 concentration should be in the specific range; otherwise, the experiment at this condition of outdoor PM10 concentration should be reconducted again.
Before the experiment, the air purifier was used to purify the indoor particulate pollution concentration to a lower level. Then, the influence of outdoor infiltration on indoor particulate matter was studied, respectively.
The experiment time was set as two hours. As the intelligent dust detector requires the experimenter to manually change the cutting head of 1.0
In order to further study the influence of outdoor infiltration on indoor particulate matter, the outdoor pollution concentration and the indoor pollution concentration were simultaneously measured in different days both in summer and in winter. In the experiment days, the window and door were kept closed for 12 hours. Both indoor and outdoor mass concentrations of PM1, PM2.5, and PM10 were measured by the intelligent dust detector.
One hundred thirty-six sets of data in summer and 75 sets of data in winter were collected.
Figures
The indoor particle concentration in outdoor PM10 = 200–300
The indoor particle concentration in outdoor PM10 = 300–400
The indoor particle concentration in outdoor PM10 = 400–500
The indoor particle concentration in outdoor PM10 = 500–600
The indoor particle concentration in outdoor PM10 = 600–700
Figure
Figure
Figure
Figure
In order to further compare the influence of outdoor pollution level on the indoor concentrations of different particle sizes, the maximum increase values and maximum increase rates of the mass concentrations of different particle sizes in different outdoor pollution levels are analyzed. The results are shown in Table
The variation of particles in different sizes under different conditions.
Outdoor concentration ( |
PM1 | PM1–2.5 | PM2.5–10 | |||
---|---|---|---|---|---|---|
Maximum increase value ( |
Maximum increase rate (%) | Maximum increase value ( |
Maximum increase rate (%) | Maximum increase value ( |
Maximum increase rate (%) | |
200–300 | 80 | 87.0 | 10 | 142.9 | 8 | 200.0 |
300–400 | 81 | 73.6 | 11 | 157.1 | 1 | 16.7 |
400–500 | 126 | 115.6 | 35 | 700 | 13 | 260.0 |
500–600 | 125 | 88.7 | 20 | 142.9 | 11 | 275.0 |
600–700 | 135 | 66.8 | 22 | 129.4 | 9 | 225.0 |
As shown in Table
The penetration of suspended particles in the atmosphere to the building envelope is usually expressed by the penetration factor
Penetration factor of particles with different particle sizes under each outdoor condition.
Outdoor concentration ( |
Penetration factor, |
|||||
---|---|---|---|---|---|---|
0.3–0.5 |
0.5–1 |
1–2.5 |
2.5–5 |
5–10 |
>10 | |
200–300 | 0.889 | 0.807 | 0.376 | 0.326 | 0.200 | 0.068 |
300–400 | 0.920 | 0.716 | 0.503 | 0.282 | 0.158 | 0.149 |
400–500 | 0.613 | 0.515 | 0.483 | 0.272 | 0.132 | 0.071 |
500–600 | 0.744 | 0.571 | 0.524 | 0.425 | 0.287 | 0.165 |
600–700 | 0.780 | 0.627 | 0.506 | 0.406 | 0.302 | 0.288 |
Based on the 136 sets of data in summer and 75 sets of data in winter obtained from the correlation experiment, the influence of outdoor infiltration on indoor particulate matter is further analyzed.
Figures
The relationships between the indoor PM1 concentrations and the outdoor PM1 concentrations: (a) summer; (b) winter.
Summer:
Winter:
Figures
The relationships between the indoor PM2.5 concentrations and the outdoor PM2.5 concentrations: (a) summer; (b) winter.
Summer:
Winter:
Figures
The relationships between the indoor PM10 concentrations and the outdoor PM10 concentrations: (a) summer; (b) winter.
Summer:
Winter:
As the experiment was conducted in sunny days and the windless or breezy days, Equations (
From Equations (
To sum up, the outdoor infiltration has the most significant effect on the indoor PM1 concentration. The penetration factors of 0.3–0.5
This study takes an office as the research object. Air infiltration experiment and correction experiment are carried out. Firstly, the variation characteristics of mass concentration and number concentration of indoor particles under five outdoor pollution levels are analyzed. Secondly, the maximum increase values and the maximum increase rates of the mass concentrations with different sizes are analyzed. Furthermore, the penetration factors of the particulate matter in different particle sizes are compared. Finally, the correlation between indoor and outdoor particulate matter concentration is studied in summer and winter. This paper can provide a basis for proposing measures to improve indoor air quality. Specifically, the following conclusions are obtained: The effect of outdoor infiltration on indoor particulate matter concentration is significant. And the greater the outdoor particle concentration is, the greater the impact on indoor particulate matter is. The outdoor infiltration has the most significant effect on the indoor PM1 concentration. The mass concentrations of PM1–2.5 and PM2.5–10 fluctuate with time in a small range, and there is no obvious increase. Due to different physical characteristics of particulate matter under different outdoor concentrations, the penetration factor of particles in each particle size does not increase with the increase of outdoor particle concentration. The penetration factors of 0.3–1.0 The mass concentration of indoor PM1 is more affected by the outdoor particulate matter in summer. The mass concentration of PM10 is more affected by the outdoor particulate matter in winter. Moreover, indoor particulate matter is more affected by outdoor particulate matter in winter. The tightness of building envelopes, doors, and windows should be paid enough attention. Especially in some heavily polluted areas, double doors and windows can be used.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest.
This research has been supported by the Fundamental Research Funds for the Central Universities (Grant no. 2018MS110) and the Natural Science Foundation of Hebei Province (Grant No. E2016502035).