We have demonstrated firstly an easy and low-cost approach to synthesize single-walled carbon nanotubes (SWCNTs) by direct current arc discharge in low-pressure air with Ni/Y as catalysts. Experimental results show that the as-synthesized SWCNT diameter is in the range of 1.29-1.62 nm and the SWCNTs show higher oxidization temperature than those synthesized by helium arc discharge. Our findings support that oxygen in air transformed to CO during the arc discharge process, resulting in the fact that the real buffer gas in our experiments is the N-2-CO mixed gas. This synthesis strategy enables the cost down of SWCNTs and paves the way toward large-scale applications of SWCNTs.(1) (C) 2013 Elsevier Ltd. All rights reserved.