Perchlorate concentration ranges from a few to a few hundred ng kg−1 in surface and shallow‐depth snow at three Antarctic locations (South Pole, Dome A, and central West Antarctica), with significant spatial variations dependent on snow accumulation rate and/or atmospheric production rate. An obvious trend of increasing perchlorate since the 1970s is seen in South Pole snow. The trend is possibly the result of stratospheric chlorine levels elevated by anthropogenic chlorine emissions; this is supported by the timing of a similar trend at Dome A. Alternatively, the trend may stem from postdepositional loss of snowpack perchlorate or a combination of both. The possible impact of stratospheric chlorine is consistent with evidence of perchlorate production in the stratosphere. Additionally, perchlorate concentration appears to be directly affected by the springtime Antarctic ozone hole. Therefore, perchlorate variations in Antarctic snow are likely linked to stratospheric chemistry and ozone over the Antarctic.

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On the basis of these findings, the jails implemented interventions such as more suicide screening and treatment for inmates who have active substance abuse, greater consensus building in decisions about housing, and structural changes such as greater use of group-housing units and the use of barriers to prevent the inmates from jumping from balconies.

An ion chromatography-electrospray ionization-tandem mass spectrometry (IC-ESI-MS/MS) method has been developed for rapid and accurate measurement of perchlorate in polar snow and ice core samples in which perchlorate concentrations are expected to be as low as 0.1 ng L(-1). Separation of perchlorate from major inorganic species in snow is achieved with an ion chromatography system interfaced to an AB SCIEX triple quadrupole mass spectrometer operating in multiple reaction monitoring mode. Under optimized conditions, the limit of detection and lower limit of quantification without pre-concentration have been determined to be 0.1 and 0.3 ng L(-1), respectively, with a linear dynamic range of 0.3-10.0 ng L(-1) in routine measurement. These represent improvements over previously reported methods using similar analytical techniques. The improved method allows fast, accurate, and reproducible perchlorate quantification down to the sub-ng L(-1) level and will facilitate perchlorate measurement in the study of natural perchlorate production with polar ice cores in which perchlorate concentrations are anticipated to vary in the low and sub-ng L(-1) range. Initial measurements of perchlorate in ice core samples from central Greenland show that typical perchlorate concentrations in snow dated prior to the Industrial Revolution are about 0.8 ng L(-1), while perchlorate concentrations are significantly higher in recent (post-1980) snow, suggesting that anthropogenic sources are a significant contributor to perchlorate in the current environment.