Oxy-steam combustion is a promising next-generation combustion technology. Conversions of fuel-N

volatile-N

and char-N to NO and N

2

O during combustion of a single coal particle in O

2

/N

2

and O

2

/H

2

O were studied in a tube reactor at low temperature. In O

2

/N

2

NO reaches the maximum value in the devolatilization stage and N

2

O reaches the maximum value in the char combustion stage. In O

2

/H

2

O

both NO and N

2

O reach the maximum values in the char combustion stage. The total conversion ratios of fuel-N to NO and N

2

O in O

2

/N

2

are obviously higher than those in O

2

/H

2

O

due to the reduction of H

2

O on NO and N

2

O. Temperature changes the trade-off between NO and N

2

O. In O

2

/N

2

and O

2

/H

2

O

the conversion ratios of fuel-N

volatile-N

and char-N to NO increase with increasing temperature

and those to N

2

O show the opposite

trends. The conversion ratios of fuel-N

volatile-N

and char-N to NO reach the maximum values at ?O

2

?=30 vol% in O

2

/N

2

. In O

2

/H

2

O

the conversion ratios of fuel-N and char-N to NO reach the maximum values at ?O

2

?=30 vol%

and the conversion ratio of volatile-N to NO shows a slightly increasing trend with increasing oxygen concentration. The conversion ratios of fuel-N

volatile-N

and char-N to N

2

O decrease with increasing oxygen concentration in both atmospheres. A higher coal rank has higher conversion ratios of fuel-N to NO and N

2

O. Anthracite coal exhibits the highest conversion ratios of fuel-N

volatile-N

and char-N to NO and N

2

O in both atmospheres. This work is to develop efficient ways to understand and control NO and N

2

O emissions for a clean and sustainable atmosphere.