The AVRs can directly only measure positive voltages. However one can shift the DC level. The simple way is using an capacitor for so called AC coupling towards a divider that provides a DC level about mid way of the ADC range. There are alternative methods too, that can be better suited for pulse currents, that might contain an DC component.
One can protect an input from to high or to low a voltage.
For the voltage, AC coupling and maybe a little division to reduce the voltage a little (2 V RMS is about 5.6 V from peak to peak and thus a little too much for a 5 V Voltage range of the ADC.
For the current reading from a shunt (e.g. voltage drop), one would need amplification. This amplification could provide the right DC level. One might need AC coupling to counteract DC offsets of the amplifier anyway.
Current measurement with a current transformer would be even easier, as the output voltage can be chosen and is isolated. So the DC level is easy to choose from the other side.