This book systematically describes the instrument setup for the measurement of nitrate radical (NO
3
) and dinitrogen pentoxide (N
2
O
5
), as well as the mixing ratio, chemical behaviors, and atmospheric impacts of NO
3
and N
2
O
5
in Beijing, China. It also discusses the instrument design and data analysis method in detail. Based on several field measurements of NO
3
and N
2
O
5
in Beijing, it shows the variation in concentration and the budget of NO
3
and N2O5. The N
2
O
5
heterogeneous uptake coefficient was determined using various methods, and the relationship between the N
2
O
5
uptake coefficient and the particle properties was demonstrated, as well as the impact of NO
3
–N
2
O
5
chemistry to the atmospheric oxidation and the formation of particulate nitrate. These results increase our understanding of nighttime chemistry and provide insights into the role of NO
3
–N
2
O
5
chemistry in other polluted regions.