Air quality is a health topic that Chinese people have been paying close attention to in recent years. With the increase of national environmental governance, China’s air quality has been improving year by year. However, many people are still willing to add a top 10 home air purifier. So, how much can a domestic air purifier improve indoor air quality?

How much is the advertisement really true?

Atmospheric particulate matter is the primary pollutant in most cities in China, and it is also the main cause of the large-scale haze weather in China in recent years.

The increase of fuel combustion in the heating period in the northern part of the country, coupled with the meteorological conditions in some periods is not conducive to the spread of particulate matter, resulting in frequent foggy weather in the northern cities of China in the north and south of Beijing represented by the Beijing-Tianjin-Hebei region.

Studies have shown that urban residents (especially middle-aged or chronically ill patients) spend more than 80% of their time indoors, and indoor air quality has a significant impact on their health. In the short-term failure to reduce the concentration of atmospheric particulate matter, the use of artificial air purification devices to reduce indoor particulate matter concentration is one of the effective means to reduce the health risks caused by particulate exposure.

Materials and Methods

1. Measurement object and time

The study initially recruited 21 residents from Haidian District, Beijing to cooperate with the study. A total of 15 homes were included after excluding non-natural ventilation, near construction sites, indoor smokers or pet houses.

The monitoring of all dwellings was completed from November 2015 to January 2016.

2. Main equipment

The air purifier is a household HEPA purifier with a filter particulate matter and a clean air output ratio ranging from 200 to 299. It is declared to be 31 to 40 m2 by the manufacturer.

A dust monitor (hereinafter referred to as “dust meter”) is used to simultaneously monitor the indoor and outdoor PM2.5 and PM10 concentrations.

A multi-channel particle detector (hereinafter referred to as “multi-channel instrument”) is used to monitor the concentration of particles of different particle sizes in the chamber before and after the operation of the purifier.

3. Monitoring method

The purifiers are placed in the living room, and the gears are opened to the mid-range, which is more than 3 m away from the sampling head of the indoor monitoring instrument. Within 3 hours after the purifier starts running, inform the tenants not to perform indoor cleaning and reduce walking. Residents do not open windows during the monitoring period and try to reduce the number of indoor cleaning.

The monitoring instrument was installed in the residential living room of the research object in an open position 1 m above the ground. In each residential room, two sets of dust meters were used to monitor the mass concentration of PM2.5 and PM10 in real-time; a multi-channel instrument was used to monitor the concentration and mass concentration of particles with different particle sizes.

At the same time, each household uses two sets of dust meters to monitor the outdoor PM2.5 and PM10 simultaneously. The switch time is the same as that of the indoor dust meter.

The concentration of indoor and outdoor particulate matter before and after the operation of the purifier was continuously monitored for 24 h for 48 h. Informed consent was signed from the residents of the surveyed home.

The indoor and outdoor particulate matter concentration ratio (I/O value) was used as a parameter to analyze the indoor particulate matter pollution level before and after the operation of the same residential purifier.

I/O value = Cin/Cout. Cin is the concentration of certain particle sizes in the room, and Cout is the corresponding outdoor concentration.

When analyzing the short-time purification efficiency of the purifier on the particulate matter, the I/O value is not sensitive enough, and the particle removal rate η is used for analysis. η=[(C0-C1)/C0]. Among them, C0 and C1 are the indoor particulate matter concentrations after the purifier starts running and after 2 to 3 hours of operation.

result

1. The overall purification effect of the purifier on indoor particulate matter (see Table 1)

After the purifier is running, the I/O value of PM2.5 shows a significant downward trend: among them, the decline of 6 households is above 70%, the decline of 2 households is 55%~60%, and the decline of 5 households is 20%~45%. The I/O value of PM2.5 after the operation of the purifiers of 2 households (7th and 13th households) is slightly higher than before the operation.

After the purifier was operated, the I/O value of PM10 of 6 households decreased by more than 70%, and the decline of 7 households was 14%~46%. The I/O value of PM10 after the 13th household purifier is running is the same as before the operation.

 Table 1 Daily average mass concentration I/O value of particulate matter before and after purifier operation

2. Abnormal situation analysis

After the 7th household and the 13th household, the purifier was operated, the I/O value of PM2.5 increased, and the I/O value of the seventh household PM2.5 decreased by less than 20%, and the 13th household did not change.

The monitoring data of indoor and outdoor particulate matter concentration of the two households are shown (see Table 2): the mass concentration of outdoor PM2.5 and PM10 is higher at 24 h before the operation of the seventh household purifier, and the outdoor PM2.5 and PM10 mass concentration after 24 h operation. Very low; the mass concentration of outdoor PM2.5 and PM10 before the operation of the 13th household purifier was lower, and the mass concentration of PM2.5 and PM10 outside the 24h after the operation was significantly higher.

Table 2 Indoor and outdoor particulate matter mass concentration of the 7th and 13th households

3. Purifier’s short-term purification efficiency of indoor particulate matter

The PM2.5 purification rate at different points after the start of purification is shown in Figure 1. The trend of the remaining particle size purification rate curve is similar to that of PM2.5. With the increase of time, the average purification rate of PM2.5 can reach 60%~70% after about 150 minutes after the start of purification.

Table 3 PM2.5 average purification rate in a short time (<3h) after starting the purifier

discuss

In this study, the daily average values ​​of PM2.5 and PM10 in the residential room after the purifier operation were all lower than 100 μg/m3.

After running the purifier, the I/O values ​​of PM2.5 and PM10 in the room decreased significantly, but the I/O values ​​of the 7th and 13th PM2.5s were opposite to the overall trend, and the I/O value of PM10 decreased less. Not even changed.

Further analysis found that when the seventh household was operating in the purifier, the mass concentration of outdoor particulate matter decreased significantly from the previous day, and the mass concentration permeating into the room plummeted. At this low mass concentration, the purifier has a small decrease in the mass concentration of the indoor particulate matter, and its I/O value is even higher than the I/O value formed by closing the door and window to block the penetration of the particulate matter into the room when the outdoor particulate matter concentration is high. The day before the 13th household purifier was operated, the outdoor particulate matter concentration was already quite low. Under the mass concentration, if the door and window of the household are closed, the outdoor particulate matter penetrates into the room less, and the I/O value of the particulate matter is lower than the I/O value after the purifier is purified.

It is concluded that the purification efficiency of the HEPA purifier is low at low concentrations compared to the high particulate concentration.

In the winter heating period, the HEPA air purifier is used as an intervention method to effectively reduce the exposure level of PM10, PM2.5 and smaller particle size in Beijing residents.

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