“Terpene odors escaping from cannabis growing”

By Richard L. Knights, Ph.D., Blue Sky Testing Labs, Seattle

See a PDF of the full 6-page report: Terpenes escaping [RK.

See a PDF of the poster  Terpenes poster 2017 [RK (a poster presented at The Cannabis Science Conference, Portland, OR, 2017)

Excerpts below:



By Richard L. Knights, Ph.D., Blue Sky Testing Labs, Seattle

Poster presentation at The Cannabis Science Conference, Portland, OR, August 28th-30th, 2017.


After a nuisance odor in an apartment and offices came from cannabis growing in a warehouse downstairs, the levels of terpenes in the air were tested to identify and quantify the odors to verify the sources and pathways.

The most abundant terpene found was beta-myrcene, the best marker for cannabis, and the only one found above its odor threshold.

The terpene levels in the growroom warehouse kept increasing without good exhaust or adsorption, which also made a stronger odor to spread through the many leaks into adjacent rooms.

The myrcene in the apartment was far above any other homes we have tested.


• Testing data agreed that the odor was strongest in the growrooms and warehouse, the source, somewhat less upstairs, and much less and different in the showroom.

• The 4 most abundant terpenes were beta-myrcene, d-limonene, alpha-pinene, and beta-pinene (like often reported in typical finished bud).

• The best marker for cannabis odor was myrcene, being the most abundant, odorous, and unique to cannabis (rarely used in consumer products like cleaners and coatings).

• The myrcene in the apartment was much higher than typical problem homes.

• The growroom warehouse should maintain a negative pressure at all times with large exhaust fans to contain and remove odors.


Cannabis was started growing in a warehouse in a building with other tenants.  Contrary to the specific lease language, odors were soon noticed upstairs, apparently leaking up from the growrooms.  At 4, 6, and 7 months after growing startup, the air was tested to confirm the source and monitor any changes after attempts were made to reduce air leakage.

Fig1 building dwg picOBSERVATIONS

This commercial building with 2 stories shown in Figure 1 had several large growroom tents and some other rooms for bud trimming, etc., inside a large ground floor warehouse.  Beside the warehouse was a small medical marijuana retail store with a lobby and sales showroom.  On the 2nd floor upstairs were an office suite and an apartment living unit.

The air handling units were several furnaces recirculating the air in the different zones.  The warehouse had also many air cooling units to remove heat and moisture, but the only small exhaust fans were in the bud finishing room and the restrooms.  There were no large beds of activated charcoal to remove terpenes.

The warehouse ceiling and walls had been air-sealed somewhat before and between these tests.  The moisture from growing had initially caused much condensation and water damage under the office roof before some major leakage pathways were sealed before these tests.

The strongest odor was found in the warehouse and growrooms, and also strong at some leakage points around the warehouse.  The odor was much less upstairs, and even less in the showroom (except for different odors inside some bud sniffing jars).  Figure 1 also shows the apparent directions of fugitive emissions from the warehouse out through many accidental leakage pathways within the building: mostly upwards into the apartment and offices, and a small amount sideways into the showroom.

The strong flow of air blowing up through a hole in the office floor showed that the warehouse was positively pressurized relative to upstairs, even without any exhaust fans running upstairs.

A commercial neighbor adjoining the offices had sometimes been the source of odors from spray painting.


There were 6 sampling locations for the different spaces, listed from the lowest to highest levels found:

1. Outdoors — outside a north window upstairs.

2. Showroom — from the furnace air supply being recirculated from the main lobby.

3. Apartment — in the breathing air (above the warehouse).

4. Office — in the breathing air (above the warehouse and showroom).

5. Warehouse — from the furnace air supply being recirculated from the warehouse (including the growrooms and other rooms).

6. Growroom — from a hole leaking air up from the center of the warehouse ceiling through the office floor (this leakage pathway was blocked after the 1st Test, so tested only once).

These 3 sets of testing were performed over 3 months:

• 1st Test:  To confirm, quantify, and document the odor levels and source, the air was tested in all 6 locations in March, 2016, after 4 months of growing.

• 2nd Test:  To find out how much a high level in the showroom might affect the office upstairs, some terpenes were released into the showroom (from pure liquid terpenes in sample sniffing jars) just before this test, acting as a tracer gas for the showroom air.  The air was tested in 3 locations (office, showroom, and warehouse) after 6 months of growing.

• 3rd Test:  To show any possible changes, the air was tested in the same 3 locations after after 7 months of growing.


To find the concentration levels of terpenes, 1000 liters of air was sampled through charcoal sorbent tubes at 1.6 liters per minute for 10 hours.  The volatile organic compounds (VOCs) were extracted with carbon disulfide, analyzed and quantified using gas chromatography, and confirmed using mass spectrometry (GC-MS) by Analytical Chemistry, Inc., Tukwila, WA.  (In the future, sampling would be done more easily with evacuated canisters using EPA Method TO-15.)


Table 1 shows the concentration levels found of the 4 most abundant terpenes, in parts per billion parts of air (ppb) around the growrooms.  The prefixes are not used for (beta-)myrcene or (d-)limonene because they are the only common isomers.  The following graphs show the results of each test.

Tab1 Terpenes found

Results of 1st Test:

The most abundant terpenes in the warehouse center were these fragrant volatile monoterpenes from essential oils:

(1) myrcene (the common beta-myrcene) had the highest levels (68% of total terpenes found), and tracked the others well.

(2) limonene (the common d-limonene) (14%).

(3) alpha-pinene (13%).

(4) beta-pinene (5%).

Other lesser (<1 ppb) terpenes were, in decreasing order: camphene, linalool, terpinolene, carene, α-terpinene, eucalyptol, α-terpineol, and ocimene.

The graph in Figure 2 of terpene concentration levels in the air in all 6 locations shows:

• The highest levels were all found in the growroom air sampled from the warehouse central ceiling (leaking from the center of the growroom tents up into the office).  Inside the tents would have been somewhat higher.

• The next highest levels were in the air recirculating from the warehouse (including the growrooms and some other rooms).

Fig2 Terp1 4x6x1 pic• The levels all increased going from the lowest outdoors to showroom to apartment to office to warehouse, and to maximum in the growrooms (the source).  Figure 1 also shows myrcene levels found indoors.

• The office and apartment levels were about half the warehouse, showing that much of the upstairs makeup air was coming from the warehouse.

Results of 2nd Test:

Fig3 Myr12 1x3x3 spike pic

The graph in Figure 3 of myrcene in 3 locations shows how the levels increased after some was released into the showroom air.  (The initial startup levels were assumed to be below 1 ppb, like typical homes.)

• Although the showroom level spiked very high (+140 ppm), the office increased only slightly (+11), much of it likely caused by the warehouse increasing also (+16) in the pasprevious 2 months.

• α-Pinene may have another source (possibly consumer products), because it was the only one higher in 1st Test.

• Myrcene was the favorite terpene odor sampled by some veteran users from sniffing jars.

Results of 3rd Test:

Fig4 Terp123 4x1x4 grow pic

The graph in Figure 4 of terpenes in the warehouse after 7 months of growing shows:

• The levels of all terpenes continued to increase as emissions accumulated.

• Myrcene increased more than the others, possibly from different growth stages or strains.


The graph in Figure 5 of terpenes in the warehouse and office during 7 months of growing shows:

• The office decreased in the 7th month (to even below the 1st Test) after sealing some more leakage pathways, which helped the warehouse increase faster.


To determine which terpenes caused the most odor, Table 2 shows the office levels of terpenes and other odorous VOCs.

pastedGraphic_6.png  To describe how much odor each terpene contributed:

• The Odor Threshold is the level (ppb) above which people commonly notice an odor (threshold for myrcene from Guadagni, others from Nagata).  Only myrcene and heptanal were much above their thresholds.  This work agrees that myrcene threshold is below about 20 ppb, because odors had been noticed upstairs in months before this testing.

• The Odor Effect Ratio of concentrations

(= Room ÷ Threshold) gives higher numbers for odors that might be noticed more in the room.  The terpene odor here was mainly myrcene, ten times more than from limonene or pinenes.

Aldehydes can have very strong odors; here, the odor effect of heptanal might have been stronger than myrcene in the office in the 1st Test, and similar in the 2nd.

Other aldehydes and other VOCs had much less odor effect than myrcene.

• The Odor Fraction (percentage) shows how much each compound contributes to the total Odor Effects.  By this calculation, myrcene was 80% of the terpene odor in this mixture.


To put these terpene levels in the apartment into perspective, they were compared with the highest of 33 homes tested in past years because of odors or health concerns.  The worst odor problems had the highest levels, caused mostly by outgassing from new materials or finishes.

Fig6 Terpenes problems 10 pic The bar chart in Figure 6 of terpenes in the worst 10 homes shows:

• Terpenes were very low in typical homes, but higher in some new houses and from some new materials or after fire cleanup, and the highest by far in this apartment above the growrooms.

• Myrcene was dominant only in this apartment above the growrooms; other terpenes dominated all other homes.

• Myrcene in the apartment (24 ppb) was far above any of the other homes (<2).



The distribution of some VOCs found in the 1st Test as shown in the graph in Figure 7 were different from the terpenes.  Because these other VOCs were highest in the office, they apparently came from another source different from the terpenes, likely the neighbor spray painting upstairs beside the office.

The levels of terpenes in the office and apartment generally followed the warehouse, as shown above.


However, the graph in Figure 8 of myrcene and other VOCs in the office shows different behaviors on different days by groups of VOCs apparently from different sources.  These plots are of the most abundant member of each of 3 groups:

• the terpenes (increasing steadily):  myrcene (37 ppb), limonene, α-pinene, and β-pinene.

• the toluene group (high 1st & 3rd Tests):  toluene (202 ppb), methyl methacrylate (42), ethanol (35), n-butyl acetate (17), xylenes (3).

• the nonane group (high only 1st Test):  nonane (the isomer 2,3-dimethylheptane) (50 ppb), and n-heptanal (also called heptaldeyde or aldehyde C-7) (3).

The toluene group likely came from spray painting before the 1st and 3rd Tests.  The nonane group came apparently from yet another source that only happened before the 1st Test, possibly from other spray paint or solvents.


To put these levels of VOCs in perspective, they were compared with the medians found in 33 homes and 20 offices tested in past years, shown in Table 3:


These levels of VOCs in typical homes and offices show:

• The higher levels of VOCs in the office were much above typical homes and offices.


Maintain a negative pressure in the growroom warehouse at all times with large exhaust fans to contain and remove odors, heat, and moisture.



Figure 1. Building layout with myrcene leaking out from warehouse through ceiling and walls.

Figure 2. Terpene levels increasing in locations going closer to the growrooms in the warehouse.

Figure 3. Large myrcene spike released into the showroom having little effect on the other rooms.

Figure 4. Terpenes levels increasing in warehouse over 7 months of growing without adequate exhaust.

Figure 5. Myrcene levels decreasing finally in the office after sealing some more penetrations better.

Figure 6. Terpene levels found in this apartment compared with homes having various odor problems.

Figure 7. Levels of some other VOCs coming from sources that were different from the terpenes.

Figure 8. Other VOCs leaking into the office from sources different from the cannabis terpenes.

Table 1. Terpenes found in the building around cannabis growrooms in warehouse on different days

Table 2. Levels of terpenes and other VOCs found compared with odor thresholds, showing which odors might dominate.

Table 3. VOCs found in the office above cannabis compared with typical clean homes and offices.

REFERENCES for odor thresholds:

Guadagni, D. G., R. G. Buttery and J. Harris, J. Sci. Food Agric., 17, 142-144 “Odour intensities of hop oil components“ (1966) http://onlinelibrary.wiley.com/doi/10.1002/jsfa.2740170311/abstract?

Nagata: “Measurement of Odor Threshold by Triangle Odor Bag Method”, by Yoshio Nagata, in Odor Measurement Review [Ministry of the Environment, Government of Japan], 2003, pp.118-127.  (see at: http://orea.or.jp/en/PDF/Odor_Measurement_Review,.pdf)  (originally Nagata 1990, by Nagata,Y. and Takeuchi,N., Bulletin of Japan Environmental Sanitation Center, (1990), 17, pp. 77-89.)

By Richard Knights, PhD, Analytical Chemistry — indoor air quality investigations

Blue Sky Testing Labs, 8655 – 39th Av S, Seattle, WA 98118-4517

(206)-721-2583 — blueskylab@pobox.com —  www.inyourair.com

Webpage to see an online PDF of this report: inyourair.wordpress.com/terpenes-escaping/.

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“©opyright 2017 by Richard Knights — All rights reserved; may not be reproduced without permission”