Current leaks at 500 VDC
I wouldn't worry about air ionisation unless your 500 V circuit was exceptionally high impedance (many MΩ).

The wire to resistor joint would ideally have some heat-shrink insulation over it, more for strain relief and protection against electric shock than concern over ionisation.

The connection to the screw terminal has a large margin of uninsulated wire which looks tinned (though it might just be out of focus). If stranded wire is soldered together to go under a screw terminal the solder will spread under the pressure resulting in a loose connection developing over time. It's better to either leave the wire unsoldered (but with the strands twisted together) or crimp on an insulated ferrule. The wire insulation should continue up to the edge of the screw terminal (but not inside it) or finish inside the insulated boot of a ferrule.