History
Our company founder, Bo Erik Ingemar Hollsten moved from Sweden to Mexico in the early 1960s, and opened Ventilacion Industrial, S.A. (VISA
MR) by servicing Ericsson Telephone Company's climatic and HVAC-related needs (now TELMEX). Early studies were conducted in the 1970s in northern Europe, particularly the Scandinavian countries where indoor air pollution was first perceived to be a problem. The oil crisis of 1973 put a premium on saving energy, leading to new building practices that drastically reduced outdoor ventilation, thereby allowing indoor sources to build concentrations of pollutants to high levels. These building practices were first instituted in the northern countries, where they would have the greatest energy-saving effect. Also, Scandinavian countries use rather homogenous building practices, with many buildings of similar construction. This had the effect of making problems due to new construction practices immediately evident, as they simultaneously surfaced in many buildings. One of the first indoor air quality problems was noticed in approximately 100 Swedish preschools and was eventually traced to emissions of a compound (casein) from a self-leveling cement used in all the preschools. These early studies concentrated on volatile organic compounds (VOCs), using relatively inexpensive gas chromatographic methods followed by flame ionizaiton detection (GC-FID). onitors were placed in fixed locations indoors and outdoors.
With keen interest our company began monitoring and addressing similar indoor air quality issues that surfaced in Mexico City. Today, studies show that ozone exposure might be positively associated with the risk of respiratory illness in children and that it may have an interactive effect with low temperature exposure. These and the studies we have conducted since 1963 have lead to our present understanding of indoor air quality issues. In nearly every one of these studies, special measurement methods specifically for use in indoor air environments were either just being introduced or we had to design and build systems to conduct them ourselves. The following is an overview of the measurement methods, particles, and some organic gases related to the measurement of indoor air contaminants. If you would like more information on organic gases or inorganic gases as they relate to the indoor air environment, contact our Engineering Department at
info@calintec.com or visit the Environmental Protection Agency.
Principles
Only low flows are possible indoors, so only a small amount of material can be collected on filters. Thus, extremely stringent requirements must be placed on weighing the filters, including 24-hour or longer equilibration in weighing rooms that are controlled for temperature and humidity both before and after use in the sampler. The filters must be weighed to within about 10 millionths of a gram, and often collect only about 100 µg of material.
Measurement methods for personal exposure must meet even strickter requirements. Size must be reduce to about a liter, weight to less than a kilogram, and noise to a level low enough not to interfere with ordinary conversation. Airflow for pumps must also be reduced, such that filters may collect only 20 to 30 µm of inhalable or fine particles over a 12-hour period and must be weighed to within 5µg to provide adequate precision. Sorbents may be limited to collecting 15 to 20 liters of air over a 12-hour period.
PARTICLES
Sampling
CAL-IN measures particles by determining their weight on a filter (i.e., gravimetric methods) or (in the past) by counting them (i.e., optical methods). Historically, most the measurement methods we have used and that are employed in environmental field studies have been gavimetric.
Analysis
Particles collected on filters can be analyzed for their elemenal context using either X-ray fluorescence (XRF) or proton-induced X-ray emission (PIXE). Teflon filters are often employed to avoid the high elemental background of quartz fiber filters. Depending on air concentrations and volume of air sampled, up to 30 or 40 elements can be analyzed using one of these methods.
Particle-bound organics such as the heavier PAHs can also be analyzed following the collection of a sample. Since the lighter PAHs are often in the vapor phase, and medium-weight PAHs may exist in both aerosol and gaseous states, a combination of a filter and a sorbent is sometimes used to collect all the PAHs in both states, with subsequent extraction of the filter and sorbent together. This method provides an accurate total but does not allow for identification of the relative amounts in the vapor and particle stage. A method that can determine the phase distribution more exactly employs a diffusion denuder followed by a filter and sorbent.
VOCs
Sampling Methods
An early method developed for occupational exposures (generall for concentrations in the rante of 10-100 parts per million for a given VOC) was the use of a sorbent (usually activated carbon) in order to concentrate the VOCs. They are then recovered by a solvent such as carbon disulfide and analyzed by gas chromatography.
In the early 1980s, passive badges employing activated charcoal were developed for use in occupational sampling. The badges operate on the principle of diffusion and often are operated over an 8-hour workday to provide an integrated average exposure for comparison to the occupational standards (e.g., the threshold limit value, or TLV). The manufacturing process for these badges leave residues of VOCs on the activate carbon making the badges unsuitable for short-term sampling at environmental concentrations, which are usually at part-per-billion (ppb) levels. However, the high background contamination on the badges can be overcome by extending the time of sampling to a week or more.
The background problems associated with activated charcoal, as wel as problems in obtaining reliable recoveries of sorbed chemicals, led to a search for a more suitable sorbent. A polymer known as Tenax was widely adopted during the 1970s as a more reliable sorbent that charcoal for ppb levels. Tenax, properly cleaned, has very low background contamination for almost all VOCs of interest. It also is stable at temperatures of up to 250 degrees Celcius, allowing thermal desorption instead of solvent desorption. Drawbacks include artifact formation of several chemicals (e.g., benzaldehyde and plenol) and an inability to retain highly volatile organic chemicals (e.g., vinyl chloride and methylene chloride).
In the late 1980s, attempts were made to combine the best attributes of charcoal and Tenax into a multisorbent system. Newer types of activated charcoal (e.g., Spherocarb and Carbosieve) were developed to provide more reliable recoveries. Tandem systems employing Tenax as the first sorbent and activated charcoal as the second, or backup, sorbent were employed. The Tenax colelcted the bulk of the VOCs and the activated charcoal collected those more volatile VOCs that "broke through" the Tenax.
Direct (Whole Air) sampling was first developed in the 1970s for upper atmosphere sampling, and avoids the sorption-desorption step, which should theoretically allows less change for contamination; however, it requires great sensitivity on the part of the detection instruments. The method may involve real-time sampling in mobile laboratories, with direct injection of the air sample into a cold trap attached to a gas chromatographer (GC), or sampling in evacuated electropolished aluminum canisters for later laboratory analysis.
Analysis
Samples are usually analyzed by first separating the components using gas chromatography (GC). Three detection methods in common use are flame ionization (FID), electron capture (ECD), and mass spectrometry (MS). Only GC-MS has the ability to identify unambiguously many chemicals. Neither GC-FID nor GC-ECD is able to separate chemicals that coelute (i.e., emerge from the chromatographic column at the same time). Also, GC-FID response is depressed by halogens such as chlorine, so it s not suitable for samples containing halogens. On the other hand, CG-ECD is extremely well suited to measuring halogens at very low concentrations. Mass spectrometry, by breaking chemicals into fragments and then identifying these fragments, often is capable of differentiating even among coeluting chemicals. However since chemicals are identified by comparing these mass fragment spectra to existing libraries, and the libraries are incomplete, even GC-MS identifications are often tentative or mistaken.
Pesticides
The basic sorbent employed is polyurethane foam (PUF), which can be analyzed for scores of the "traditional" chlorinated pesticides, including DDT, chlordane, aldrin, dieldrin, and others in this general category. Some organophosphate pesticides such as chlorpyrifos can also be collected on PUF and analyzed by multianalyte methods.
Nitrosamines
A convenient sampling and analysis method was developed for determining volatile N-nitrosamines in ETS because of their potency as carcinogens. The method employs Thermosorb/N cartridges to collect and fix the N-nitrosamines. Excellent recoveries of 96± 5% were obtained for the four most common N-nitrosamines.
Carbon Monoxide
CAL-IN uses large nnumber of continusous monitors, both active (pumped) and passive (diffusion) for CO. Most are electrochemical, depending on counting the electrons produced when CO is oxidized to CO
2. Precision of these monitors is generally very good, with typical errors in the order of 0.1ppm. Interferences can be a problem in some cases. Given the number of beans consummed in Mexico, endogenously produced hydrogen can be a problem when monitors are used for breath analysis!
Nitrogen Oxides
A useful monitor for NO
2 is the Palmes Tube, which consists of a short plastic tube with a filter soaked with a solution of triethanolamine, which reacts with NO
2 and can later be quantitated by a colorimetric method. The system has a sensitivity of about 600 ppb/h, so that for typical environmental concentrations of 10-20 ppb, a sampling period of a few days is sufficient to obtain a measurement.
The Yanagisawa Badge, which employs a baffle to reduce sensitivity to wind velocity, and has a smaller length-to-area distance to improve diffusion rate, is another monitor, which has some improvements. The badge is about ten times as sensitive as the Palmes Tube, allowing shorter collection periods.
AIR EXCHANGE
Air exchange is one of several crucial ancillary variables in understanding indoor-outdoor relationships. Air exchange rates can have an important influence on pollution levels in your home or office. For example, if outdoor air is cleaner than indoor ar, as is true for most VOCs and most pesticides, then it will improve matters to open the windows, turn on fans, or otherwise increase the air exchange rate. On the other hand, during times of high outdoor air pollution, closing the windows or otherwise reducing air exchange rates can have a protective effect. This is particularly true for particles, which deposit on walls and thus are removed from indoor air - the lower the air exchange rate, the more particles will be removed from the air. Tracer gases such as sulfur hexafluoride (SF
6) or other perfluorinated tracers (PFTs) not found in nature are generally used to measure air exchange rates.
Use of the perfluorinated tracers provide the most accurate measurement of air exchange, but less expensive methods can be employed. Because of the general decline of CO emissions from automobiiles, many areas have very low CO concentrations just outside the building.