More outside groups are jumping into the Massachusetts Senate fray.

The League of Conservation Voters launched a $350,000 television ad campaign on Thursday on Boston-area broadcast and cable television that will air through election day on Jan. 19. In the ad, the environmental group goes after state Sen. Scott Brown’s (R) opposition to the American Clean Energy and Security Act, which would impose a cap-and-trade system to regulate carbon emissions.

“On Tuesday, we can say yes to clean energy jobs and energy independence by electing Martha Coakley as our new senator,” the ad says. The group has already endorsed Coakley (D), the Massachusetts attorney general, citing her past work including, petitioning the EPA that greenhouse gases pose a threat to public health and welfare.

The National Rifle Association has also invested in the race this week to help elect Brown. The gun rights group’s Political Victory Fund disclosed nearly $20,000 in spending on direct mail.

CQ Politics rates the general election contest Leans Democratic.

To follow all the 2010 Senate races, check out the CQ Politics election map.