How do current pollution levels in Los Angeles compare to the 1970s?
The air quality in Los Angeles does not meet federal air quality standards.  That being said, the air quality has improved immensely since the 1970s.  

From the California Air Resource Board, in 1965 the maximum one-hour ozone concentration was 0.58 ppm.  Since then, that number has come down to about 0.12 ppm.  You can obtain the latest ozone data from EPA.  See a  30 year ozone trend image below from the South Coast Air Quality Management District:



Particulate matter is a bit tougher to quantify.  PM10 (coarse and fine particles together) has been tracked since the late 80s, but PM2.5 (fine particles) has only been tracked since 1999.  You can read a bit about it here. 

The reduction in particulate matter has not been as dramatic as ozone.  This makes sense, though, since ozone is a secondary pollutant whose precursors (NOx and VOCs) largely come from vehicle tailpipes.  NOx and VOC emissions from vehicles has decreased significantly in recent years, especially with fleet turnover.  In contrast, coarse and fine particulate matter come from many different sources, e.g. road dust, agriculture, cooking, etc. which is difficult to control since rain is the major control method.