Reactive uptake of ammonia to secondary organic aerosols: kinetics of organonitrogen formation

Abstract

Abstract. As a class of brown carbon, organonitrogen compounds originating from the heterogeneous uptake of NH 3 by secondary organic aerosol (SOA) have received significant attention recently. In the current work, particulate organonitrogen formation during the ozonolysis of α-pinene and the OH oxidation of m-xylene in the presence of ammonia (34-125 ppb) was studied in a smog chamber equipped with a high resolution time-of-flight aerosol mass spectrometer and a quantum cascade laser instrument. A large diversity of nitrogen-containing organic (NOC) fragments was observed which were consistent with the reactions between ammonia and carbonyl-containing SOA. Ammonia uptake coefficients onto SOA which led to organonitrogen compounds were reported for the first time, and were in the range of ∼ 10 −3 -10 −2 , decreasing significantly to < 10 −5 after 6 h of reaction. At the end of experiments (∼ 6 h) the NOC mass contributed 8.9 ± 1.7 and 31.5 ± 4.4 wt % to the total α-pineneand m-xylene-derived SOA, respectively, and 4-15 wt % of the total nitrogen in the system. Uptake coefficients were also found to be positively correlated with particle acidity and negatively correlated with NH 3 concentration, indicating that heterogeneous reactions were responsible for the observed NOC mass, possibly limited by liquid phase diffusion. Under these conditions, the data also indicate that the formation of NOC can compete kinetically with inorganic acid neutralization. The formation of NOC in this study suggests that a significant portion of the ambient particle associated N may be derived from NH 3 heterogeneous reactions with SOA. NOC from such a mechanism may be an important and unaccounted for source of PM associated nitrogen. This mechanism may also contribute to the medium or long-range transport and wet/dry deposition of atmospheric nitrogen.

Chemical Composition and Reaction Mechanisms for Aged p‐Xylene Secondary Organic Aerosol in the Presence of Ammonia

“…The obtained real component ( n ) of the NH 3 ‐aged biogenic SOA did not change significantly, but the imaginary part ( k ) increased from k = 0.000 to k = 0.030 for the NH 3 ‐aged limonene and α‐humulene SOA. Also, the formation of particulate nitrogen‐containing organic products during the photoxidation of m ‐xylene and ozonolysis of α‐pinene with NH 3 were studied by Liu et al . A number of organonitrogen fragments were observed, which were in accordance with the reactions between NH 3 and the carbonyl constituents of SOA.…”

“…The potential chromophores were likely imidazole compounds, such as imidazole and imidazole‐2‐carbaldehyde, which were formed from the reactions between NH 3 and carbonyl‐containing SOA. Although carboxyl compounds, whose IR absorbance bands shown in Figure (for the aged p ‐xylene SOA with 20 ppm NH 3 and 2.0 ppm NO) appear at 1649 cm −1 for the stretching of C═O, 1087 cm −1 for the bending vibration of O─H, and stretching of C─O were observed, the notable peaks appear at 1518 cm −1 for bending of N─H, 1743–1698 cm −1 for stretching of N═C, and 1457 cm −1 for stretching of C─N, confirming that the 280 nm chromophores correspond to imidazole compounds. Also, the observed ALTOFMS fragments of CH 2 N + ( m/z 28), C 2 H 3 N + ( m/z 41), and C 3 H 3 N 2 + ( m/z 67) in the next section indicate that imidazole compounds were formed in the aged p ‐xylene SOA with NH 3 and NO.…”

“…Strong peaks belonging to the C x H y N n dominate the spectrum at m /z 28 (CH 2 N + ), 41 (C 2 H 3 N + ), and 67 (C 3 H 3 N 2 + ), demonstrating that imidazole species are formed in the NH 3 ‐aged p ‐xylene SOA with NO . These results are in accordance with those of previous studies, which found a notable increase in the fraction of organonitrogen compounds for aged α‐pinene SOA and m ‐xylene SOA with NH 3 . It is well known that α‐dicarbonyls such as glyxoxal and methylglyxoxal are the major particulate products from the photoxidation of p ‐xylene .…”

“…It is well known that α‐dicarbonyls such as glyxoxal and methylglyxoxal are the major particulate products from the photoxidation of p ‐xylene . According to the experimental results of Liu et al . and Zhang et al ., heterogeneous reactions of NH 3 with carbonyl compounds in SOA lead to the generation of imidazole products after the NH 3 uptake onto the SOA.…”

Development of an inorganic and organic aerosol model (CHIMERE 2017&lt;i&gt;β&lt;/i&gt; v1.0): seasonal and spatial evaluation over Europe

“…It could also be important to take into account the formation of some acid organics/ammonium salt which can be in competition with ammonium nitrate formation. Some organonitrogen compounds were also found by condensation of ammonia onto organic aerosols (Liu et al, 2015).…”