How do i turn this ParticleEmitter on my Hand Off and on?

In order to turn the effect off, you need to make a variable for the effect's current status.

This way, when you press the key you can check the status. If it is on, turn it off.. and if its off, turn it on.

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local status = false; --Current status of effect

function KeyDown(key)
	key = key:lower()
	local hotkey = script.hawtkey
	local particle = player.Character.RightHand:findFirstChild("ParticleEmitter")
	if key == hotkey.Value then
		if not status then --Check status
			--If it is off, turn on
			status = true;
			local sparkel = Instance.new("ParticleEmitter")
			sparkel.Texture = "http://www.roblox.com/asset/?id=492009091"
			sparkel.Size = NumberSequence.new(1)
			sparkel.Rate = 200
			sparkel.Speed = NumberRange.new(20)
			sparkel.Lifetime = NumberRange.new(50)
			sparkel.Parent = player.Character.RightHand
			sparkel.Name = "Effect";
		else --If if is on, turn off.
			local sparkel = player.Character.RightHand:FindFirstChild("Effect");
			if sparkel then
				sparkel:Destroy();
			end
			status = false;
		end
	end
end

mouse.KeyDown:connect(KeyDown)