air particles

Well, actually we can feel air particles. If there is sufficient air pressure on a hair follicle it will move and trigger sensory neurons in your skin. Local air pressure could be increased by moving your arm through the air, or being near something else that is blowing air at you. If air particles are completely still, then the pressure is zero. But air particles are not completely still; they are moving around a great deal, that is why they are in gaseuous form. But sure, they are relatively still, relatively low pressure, so it's relatively hard to feel them.