Resumen
The results of eight years of radiometric measurements of the zenith opacity at 210 GHz (1.4mm) over San Pedro Mártir Sierra, Mexico, are presented. The measurements cover the period from 1995 to 2002. Observations were carried out during 1570 days. The total median sky opacity at this frequency was 0.23 nepers. The median values of day-time and night-time zenith opacity of 0.25 and 0.20 nepers respectively were found. During the Summer, the opacity rises to a maximum in August due to the water vapor carried by the American Monsoon. Results for 1998 reflect the presence of El Niño activity during that year.
