Noticed significant changes in indoor CO2 and not sure if related to atmospheric (rain/sun) or other reason so measured 144 samples between Aug 26 and Sep 26. If not related to rain and sun then might expect average, spread, variance, to be similar. Compared indoor CO2 to 1) azimuth 0-179, usually front yard and leeward side of residence 2) azimuth sun 180 359, usually back yard and windward side 3) dark and 4) precipitation other than 0 and 5) declination of sun. Found no significant difference in means except declination of sun between northern declination and southern declination(p=0.03). Big differences in variance with lowest variance during dark and rain with highest variance of indoor CO2 with sun in front yard. Declination changes coincided with big drop of cooling degree days and open house conditions. Spread of 144 partial pressure CO2 measures was 31.2 torr. Still do not know why CO2 changes so much but think it is related to opening windows. No measures of clinical relevance were measured or reported.