It seems higher levels of trichloroethylene than this are/were common, even outdoors: (note this data is 10-20 years old)<p><i>Reported worldwide background levels vary from <17 to 109 ng/m3. In rural areas levels of 0.10–0.68 µg/m3 have been reported (4,5). In urban areas levels are higher. In European cities, the reported range is 0.04–64.1 µg/m3 (mean concentrations 0.8–18.5 µg/m3). For Germany,
5–15 µg/m3 is reported as the typical concentration range for urban areas (4). In the United States, concentrations in municipal areas ranged from 0.03 to 13.5 µg/m3 (mean
concentrations 0.5–2.1 µg/m3) (4); the average for urban areas of 2.5 µg/m3 (0.46 ppb) that resulted from a compilation of data in 1982, is in agreement with more recent measurements (3). Mean concentrations (24-hour composite samples averaged over 1–12 months) in 11 Canadian cities ranged from 0.7 to 0.96 µg/m3 (5).</i><p><i>The median value for indoor air from the 2031 entries in the United States Environmental Protection Agency (EPA) data base on volatile organic contaminants (VOC-AMBI) is 0.68
µg/m3 (0.125 ppb); the average value was 7.36 µg/m3
(1.347 ppb) (6). In Canada, mean indoor air concentrations of up to 165 µg/m3 with an overall mean value of 1.4 µg/m3
have been reported (5). Concentrations measured in several western European countries varied from 0.76 to 1200 µg/m3
. Concentrations are generally higher in indoor air than outdoors (4). An important source for trichloroethylene in indoor air is volatilization from contaminated
water (7). </i><p><a href="http://www.euro.who.int/__data/assets/pdf_file/0003/123069/AQG2ndEd_5_15Trichloroethylene.pdf" rel="nofollow">http://www.euro.who.int/__data/assets/pdf_file/0003/123069/A...</a> (from 2000)<p>This article:<p><i>The problem at Google was discovered when routine air sampling found TCE at a level of 7.8 micrograms per cubic meter in a hallway of one building on Nov. 21. The EPA was notified as required. It is unclear how long the levels had been above the danger threshold. The previous sampling in September 2010 found nearly undetectable levels.</i><p><i>In an effort to reduce the vapors, workers sealed cracks in floors and walls where TCE might get in. But despite their efforts, samples collected on Dec. 29 found the problem was getting worse: TCE exceeded the 5-microgram safety threshold in five locations in two of the four buildings.</i>