Group 8 - Task 3
Handed in 21-03-2007
ENVIRONMENTAL EXPOSURE TO AIRBORNE PARTICLES - Impact of ozone on ultra-fine particles in indoor air _________________________
_________________________
_________________________
Brian Hurup-Felby, s958311
Toste Lund, s031758
Thomas Norling, s032457
_________________________
_________________________
Ulrik Pedersen, s032459
Louise F. Wille, s022383
INTRODUCTION Indoor ozone and the products derived from reactions initiated by indoor ozone are potentially damaging to both human health and materials. This is stated in Weschler, 2000 and 2004. Particles can be emitted from many indoor sources: Occupants and pets, cooking, smoking, building materials, paint, furnishing, pesticides or mold and fungi (Weschler, 2007). Furthermore, reactions between ozone and various terpenes Figur 1: Sensory assessment sheet in indoor environments can produce a significant increase in the numbers and mass-concentrations of sub-micron particles (Weschler, 1999). The indoor ozone concentration is dependant on a number of factors, including the outdoor concentration, air exchange rates, indoor emission rates, surface removal rates, and reactions between ozone and other chemicals in the air. But apart from this, there are a number of indoor sources of ozone: photocopiers, laser printers, electrostatic precipitators and ozone generators (sold as ‘air purifiers’) (Weschler, 2000). The particle concentration rises when there are chemicals in the air that can react with the highly reactant ozone, O3. Ozone reacts with different chemicals to produce chemicals via surface and gas phase reactions. As more and more particles are generated, these particles also grow larger and larger as they bump into each other (Weschler, 2007). In this experiment, the particle emission stemming from a reaction between ozone and a component in a commonly used air freshener, a so-called ‘Volatile Organic Compound’, or VOC, in a room is measured and compared to the sensory assessment of a group of test persons. Also, the particle levels at different locations indoors and outdoors is measured in order to make a comparison with the test result, and to give an overview of the particle levels in the immediate surroundings at DTU. Indoor environment is perceived differently by different human beings. This experiment is conducted to find out how people perceive the indoor environment in a room, and how this perception changes when the level of particles rises. Objectives The objectives of this experiment are: • •
evaluation of different particle levels normally occurring indoors and outdoors to understand the aerosol formation in indoor air as a result of a reaction between ozone and a component, a VOC, from a commonly used air freshener
DTU Course 41722 - Group 8 – Task 6
METHODS The experiment consists of two parts: Part 1: Assessment of the air quality in a test facility, under three different conditions. Part 2: Measurement of particle levels at different locations indoors and outdoors on different field locations Part 1, Facilities: The facilities for this part of the experiment consist mainly of one test room, where test persons are sent in to evaluate the air quality. There are three test conditions: Condition 1: The room is assessed without any additions, only a fan is turned on to provide air movement in the room and ensure that the air is well mixed. An ‘X’ marked on the floor of the room ensures that all test persons are in the same spot when assessing the air quality. Condition 2: Two air fresheners are placed in the room to generate particles in the room. Condition 3: An ozone generator is started; the air fresheners are still present. This is done to generate even more particles in the room, as ozone, O3, is a highly reactant gas that reacts with components in the air freshener and creates particles in the air. In all three conditions, 15 test persons were sent in one by one to assess the air quality. They were asked to put their evaluation down on a scale from ‘Clearly Unacceptable’ to ‘Clearly Acceptable’ on a sensory assessment sheet (see Figure 3) The particle level in the room was at the same time measured with an array of instruments: Instruments: The instruments used to measure the particle levels are: • • •
An ozone meter to measure the level of ozone in the air ‘Lasair Particle Measuring System’ that measures particles in the size range 0,1µm – 18µm ‘P-trak Ultrafine Particle Counter’ measuring particles in the size range smaller than 0,1µm
The measurements were carried out at times as shown on figure 2.
FIGURE 3: SENSORY ASSESSMENT SHEET
FIGURE 2: MEASUREMENT PROCEDURE
2
DTU Course 41722 - Group 8 – Task 6
CALCULATIONS: Based on the sensory assessments from the test persons, the percentage of dissatisfied persons can be calculated using the following formula:
⎛ exp(−0.18 − 5.28 ⋅ ACC (t ) PD = ⎜⎜ ⎝ 1 + exp − 0.18 − 5.28 ⋅ ACC (t )
(
)
⎞ ⎟ ⋅ 100 (I) ⎟ ⎠
Where: PD = Percentage of dissatisfied with air quality [%] ACC (t ) = Average Vote of Air Acceptability
The Average Vote of Air Acceptability is found from the sensory assessment sheets filled out by the test persons. To calculate the ACC (t ) , the distance on the columns from the mark made by the test person to the end of the line is simply measured, compared to the full length of the line, and an average is calculated. The Lasair measures the particle level in particles / (ft3*min). To convert this to parts/cm3, the following equation is used: part / ft 3 Particles / cm = 28316cm 3 / ft 3 3
(II)
28316 is the number of cm3 pr ft3, and the measurement took 1 min and the air flow was approx 0,0018 ft3 pr min
Where: Part 2, Facilities:
For part 2, a so-called ‘P-trak Ultrafine Particle Counter’ was used to make field measurements on different locations indoors and outdoors at DTU. The places measured were: • • • • • •
DTU, Building 101, PF Bookstore & DTV (Library) DTU, Building 101, Canteen DTU, Building 101, S-huset (Student House) Rævehøjvej, the bridge over the motorway at DTU Motorway at DTU DTU, Building 116, Entrance Hall & Databar
These measurements are showed in Figure 6. The P-trak doesn’t measure the ozone level in PPB, but in µg/m3, so to convert this scale, the following equation is used: PPB = (µg/m³ * 24,45) / MW O3 Where:
(III)
MW O3 = molecular weight of ozone (48 µg/mole) and 24,45 is the volume of 1 mole of air at 25˚Celcius [liters]
3
DTU Course 41722 - Group 8 – Task 6
RESULTS It is evident in the data obtained in this experiment that the particle level rises when ozone is generated in a room where an air freshener is placed. These measurements are seen on figure 3 and 4.
Particle concentration [Particles pr cm3]
Lasair Lasair Measurements, Measurements, Converted converted
FIGUR 4: THE LEVEL OF PARTICLES, SIZE RANGE 0,1 µm – 2 µm
In figure 3 it is seen how the level of small particles (d=0,1) decreases after a certain amount of time (around 15:15) this can be explained by the fact that the small articles grow larger by ‘bumping in’ to each other, and therefore start appearing on the larger scale in stead (d=0,2)
Test persons enter the room
Ozone Generator is started
Air Freshener is started
Particle concentration [Particles pr cm3]
P-Trak Measurements
FIGUR 5: THE LEVEL OF ULTRAFINE PARTICLES, SIZE RANGE < 0,1 µm
In figure 4, it is seen how the particle level decreases slightly when the air freshener is started. This is because the background level of ozone on the test day was fairly high due to good weather conditions (will be shown later), so the ozone already present in the air starts to react with the VOC’s in the air freshener. It is also clear how the particle level rises rapidly when the ozone generator is started (at 14:30). The ozone level decreases when test persons enter the room, because of the door being open for short amounts of time (15:10->).
4
DTU Course 41722 - Group 8 – Task 6 Another thing that is evident in the data is that the amount of people who were dissatisfied with the indoor environment in the room is significantly higher when the particle level rises. These results are shown in Table 1, calculated by equation (I)
TABLE 1: PERCENTAGE OF PEOPLE DISSATISFIED WITH THE INDOOR ENVIRONMENT
ACC(t) PPD
Condition 1 0,24 19,13
Condition 2 -0,25 75,50
Condition 3 -0,52 92,84
For part 2 of the experiment, the following concentrations of ultrafine particles were found:
FIGURE 6: THE RESULTS OF THE IN- AND OUTDOOR MEASUREMENTS
The coloured areas in Figure 6 are the specific times, when measurements were made with the ‘P-trak Ultrafine Particle Counter’. TABLE 2: OZONE LEVELS IN COPENHAGEN
On the Danish National Environmental Research Institute’s homepage, measurements of the air quality in Denmark are logged. TABLE 2 shows the ozone concentration in Copenhagen on March 14th, 2007, the same day as we made our measurements. As seen, the ozone levels for the particular day are quite high; ca. 39 PPB ~77 µg/m3. A medium level in DK for March is about 40-60 µg/m3, equivalent to 20-30 PPB1 which is considered a low ozone concentration. 31-60 PPB is a medium concentration, and 61-92 PPB is considered a high concentration. 2
Time 15-16 14-15 13-14 12-13 11-12 10-11 09-10 08-09
O3 µg/m3 83,16 83,15 80,68 79,80 77,13 74,72 68,68 61,66
Average outdoor background
1 2
O3 PPB 42 42 41 41 39 38 35 31 39
Reference of outside levels http://www2.dmu.dk/atmosphericenvironment/byer/forside.htm DMI http://www.dmi.dk/dmi/index/danmark/ozon.htm
5
DTU Course 41722 - Group 8 – Task 6
DISCUSSION In condition 1 most of the test persons felt comfortable in the room, and the calculated PPD shows that 19% were dissatisfied with the air quality. The level of ozone was here close to the outdoor level, and the particle count low. After the air fresher was placed in the room, 75% of the test persons were dissatisfied with the air quality. This complies with the particle level slightly rising in the room because the air freshener emits VOC’s. Moreover, there was a very heavy odour in the room, due to the concentration of air fresheners being quite high. The amount of dissatisfied persons increases when ozone is added to the room by the ozone generator, and as many as 93% of the test persons felt uncomfortable in the room. This complies with the level of particles being significantly higher at this point due to the chemical reactions between ozone and VOC’s. There are a few sources of error or deviation in this experiment: Some of the test person came from south European countries, and it was found that a larger number of them find the odour of the air fresher comfortable. The opposite was the case with the Danish test persons. This indicates that the nationality influences the test persons’ reaction to the odour of the air fresher, and subsequently to their mark on the sensory assessment sheet. This is only a peculiar finding, though, and it has not been further investigated in this task. Other sources of error are of course the low number of test persons, the fact that many test persons spoke a poor English and might have had difficulty understanding the Sensory Assessment Sheet, even after a thorough explanation, the fact that many test persons knew the experiment beforehand and might have had a biased approach as to what to answer in the different conditions, and finally that a few test person were affected by a cold that made it hard for them to smell/sense the air in the room. Particle levels in the field measurements show very high concentrations in some of the locations, specifically the library and the motorway. Levels, that are as high as or higher than those produced in the experiment. The level of particles at the motorway reached up to 102.000 particles pr cm3 depending on the traffic, even in a windy weather condition. In the bookstore a level of 35.000 particles pr cm3 was measured. This goes to show that, among others, people who work in the bookstore at DTU and people who live close to the motorway are exposed to high concentration of particles in the air on a daily basis. This most likely gives them a sense of dissatisfaction, and might even influence on their health.
CONCLUSION This experiment clearly shows that high levels of particles make people feel uncomfortable. There is no doubt in the results that people do indeed feel uncomfortable in rooms with high concentrations of particles. The particle levels found in many field measurements were much higher than that in the test room, so there is a great probability of people feeling uncomfortable in the immediate surroundings at DTU, for example people living close to the motorway. This is most likely also the case in any other locations that resemble these. This might be a risk to the general health of a large part of the population, as particles can be inhaled and circulate in the body. It is not yet proven, though, how dangerous particles are, but as stated in Weschler, 2004, it could be very harmful. As stated in Schneider et al., 2003, more research is needed before a clear standard can be set, but all the circumstantial evidence is starting to show, in this experiment none the less.
REFERENCES /1/ T. Schneider, et al.: “EUROPART”. Airborne particles in the indoor environment. A European interdisciplinary review of scientific evidence on associations between exposure to particles in buildings and health effects, 2003 /2/ Weschler, Charles J and Shields, Helen: Indoor Ozone/Terpene reactions as a source of indoor particles; 1999 /3/ Weschler, Charles J: Ozone in indoor environments: Concentration and Chemistry, 2000 /4/ Weschler, Charles J: New directions: Ozone initiated reaction products indoors may be more harmful than ozone itself, 2004 /5/ Weschler, Charles J: Chemicals in Indoor Air – lecture at DTU, February 21st 2007 6